Feature selection with PCA
Overview
Teaching: 45 min
Exercises: 2 minQuestions
How can PCA be used as a feature selection method?
Objectives
Multivariate Regression with PCA
Predict if house sales price will be high for market from house characteristics
Ames housing dataset data
load dataset
from sklearn.datasets import fetch_openml
housing = fetch_openml(name="house_prices", as_frame=True, parser='auto')
view data
df = housing.data.copy(deep=True)
df = df.astype({'Id':int}) # set data type of Id to int
df = df.set_index('Id') # set Id column to be the index of the DataFrame
df
all feature names
print(df.columns.tolist())
['MSSubClass', 'MSZoning', 'LotFrontage', 'LotArea', 'Street', 'Alley', 'LotShape', 'LandContour', 'Utilities', 'LotConfig', 'LandSlope', 'Neighborhood', 'Condition1', 'Condition2', 'BldgType', 'HouseStyle', 'OverallQual', 'OverallCond', 'YearBuilt', 'YearRemodAdd', 'RoofStyle', 'RoofMatl', 'Exterior1st', 'Exterior2nd', 'MasVnrType', 'MasVnrArea', 'ExterQual', 'ExterCond', 'Foundation', 'BsmtQual', 'BsmtCond', 'BsmtExposure', 'BsmtFinType1', 'BsmtFinSF1', 'BsmtFinType2', 'BsmtFinSF2', 'BsmtUnfSF', 'TotalBsmtSF', 'Heating', 'HeatingQC', 'CentralAir', 'Electrical', '1stFlrSF', '2ndFlrSF', 'LowQualFinSF', 'GrLivArea', 'BsmtFullBath', 'BsmtHalfBath', 'FullBath', 'HalfBath', 'BedroomAbvGr', 'KitchenAbvGr', 'KitchenQual', 'TotRmsAbvGrd', 'Functional', 'Fireplaces', 'FireplaceQu', 'GarageType', 'GarageYrBlt', 'GarageFinish', 'GarageCars', 'GarageArea', 'GarageQual', 'GarageCond', 'PavedDrive', 'WoodDeckSF', 'OpenPorchSF', 'EnclosedPorch', '3SsnPorch', 'ScreenPorch', 'PoolArea', 'PoolQC', 'Fence', 'MiscFeature', 'MiscVal', 'MoSold', 'YrSold', 'SaleType', 'SaleCondition']
Reminder to access the Data Dictionary
from IPython.display import display, Pretty
display(Pretty(housing.DESCR))
Ask a home buyer to describe their dream house, and they probably won't begin with the height of the basement ceiling or the proximity to an east-west railroad. But this playground competition's dataset proves that much more influences price negotiations than the number of bedrooms or a white-picket fence.
With 79 explanatory variables describing (almost) every aspect of residential homes in Ames, Iowa, this competition challenges you to predict the final price of each home.
MSSubClass: Identifies the type of dwelling involved in the sale.
20 1-STORY 1946 & NEWER ALL STYLES
30 1-STORY 1945 & OLDER
40 1-STORY W/FINISHED ATTIC ALL AGES
45 1-1/2 STORY - UNFINISHED ALL AGES
50 1-1/2 STORY FINISHED ALL AGES
60 2-STORY 1946 & NEWER
70 2-STORY 1945 & OLDER
75 2-1/2 STORY ALL AGES
80 SPLIT OR MULTI-LEVEL
85 SPLIT FOYER
90 DUPLEX - ALL STYLES AND AGES
120 1-STORY PUD (Planned Unit Development) - 1946 & NEWER
150 1-1/2 STORY PUD - ALL AGES
160 2-STORY PUD - 1946 & NEWER
180 PUD - MULTILEVEL - INCL SPLIT LEV/FOYER
190 2 FAMILY CONVERSION - ALL STYLES AND AGES
MSZoning: Identifies the general zoning classification of the sale.
A Agriculture
C Commercial
FV Floating Village Residential
I Industrial
RH Residential High Density
RL Residential Low Density
RP Residential Low Density Park
RM Residential Medium Density
LotFrontage: Linear feet of street connected to property
LotArea: Lot size in square feet
Street: Type of road access to property
Grvl Gravel
Pave Paved
Alley: Type of alley access to property
Grvl Gravel
Pave Paved
NA No alley access
LotShape: General shape of property
Reg Regular
IR1 Slightly irregular
IR2 Moderately Irregular
IR3 Irregular
LandContour: Flatness of the property
Lvl Near Flat/Level
Bnk Banked - Quick and significant rise from street grade to building
HLS Hillside - Significant slope from side to side
Low Depression
Utilities: Type of utilities available
AllPub All public Utilities (E,G,W,& S)
NoSewr Electricity, Gas, and Water (Septic Tank)
NoSeWa Electricity and Gas Only
ELO Electricity only
LotConfig: Lot configuration
Inside Inside lot
Corner Corner lot
CulDSac Cul-de-sac
FR2 Frontage on 2 sides of property
FR3 Frontage on 3 sides of property
LandSlope: Slope of property
Gtl Gentle slope
Mod Moderate Slope
Sev Severe Slope
Neighborhood: Physical locations within Ames city limits
Blmngtn Bloomington Heights
Blueste Bluestem
BrDale Briardale
BrkSide Brookside
ClearCr Clear Creek
CollgCr College Creek
Crawfor Crawford
Edwards Edwards
Gilbert Gilbert
IDOTRR Iowa DOT and Rail Road
MeadowV Meadow Village
Mitchel Mitchell
Names North Ames
NoRidge Northridge
NPkVill Northpark Villa
NridgHt Northridge Heights
NWAmes Northwest Ames
OldTown Old Town
SWISU South & West of Iowa State University
Sawyer Sawyer
SawyerW Sawyer West
Somerst Somerset
StoneBr Stone Brook
Timber Timberland
Veenker Veenker
Condition1: Proximity to various conditions
Artery Adjacent to arterial street
Feedr Adjacent to feeder street
Norm Normal
RRNn Within 200' of North-South Railroad
RRAn Adjacent to North-South Railroad
PosN Near positive off-site feature--park, greenbelt, etc.
PosA Adjacent to postive off-site feature
RRNe Within 200' of East-West Railroad
RRAe Adjacent to East-West Railroad
Condition2: Proximity to various conditions (if more than one is present)
Artery Adjacent to arterial street
Feedr Adjacent to feeder street
Norm Normal
RRNn Within 200' of North-South Railroad
RRAn Adjacent to North-South Railroad
PosN Near positive off-site feature--park, greenbelt, etc.
PosA Adjacent to postive off-site feature
RRNe Within 200' of East-West Railroad
RRAe Adjacent to East-West Railroad
BldgType: Type of dwelling
1Fam Single-family Detached
2FmCon Two-family Conversion; originally built as one-family dwelling
Duplx Duplex
TwnhsE Townhouse End Unit
TwnhsI Townhouse Inside Unit
HouseStyle: Style of dwelling
1Story One story
1.5Fin One and one-half story: 2nd level finished
1.5Unf One and one-half story: 2nd level unfinished
2Story Two story
2.5Fin Two and one-half story: 2nd level finished
2.5Unf Two and one-half story: 2nd level unfinished
SFoyer Split Foyer
SLvl Split Level
OverallQual: Rates the overall material and finish of the house
10 Very Excellent
9 Excellent
8 Very Good
7 Good
6 Above Average
5 Average
4 Below Average
3 Fair
2 Poor
1 Very Poor
OverallCond: Rates the overall condition of the house
10 Very Excellent
9 Excellent
8 Very Good
7 Good
6 Above Average
5 Average
4 Below Average
3 Fair
2 Poor
1 Very Poor
YearBuilt: Original construction date
YearRemodAdd: Remodel date (same as construction date if no remodeling or additions)
RoofStyle: Type of roof
Flat Flat
Gable Gable
Gambrel Gabrel (Barn)
Hip Hip
Mansard Mansard
Shed Shed
RoofMatl: Roof material
ClyTile Clay or Tile
CompShg Standard (Composite) Shingle
Membran Membrane
Metal Metal
Roll Roll
Tar&Grv Gravel & Tar
WdShake Wood Shakes
WdShngl Wood Shingles
Exterior1st: Exterior covering on house
AsbShng Asbestos Shingles
AsphShn Asphalt Shingles
BrkComm Brick Common
BrkFace Brick Face
CBlock Cinder Block
CemntBd Cement Board
HdBoard Hard Board
ImStucc Imitation Stucco
MetalSd Metal Siding
Other Other
Plywood Plywood
PreCast PreCast
Stone Stone
Stucco Stucco
VinylSd Vinyl Siding
Wd Sdng Wood Siding
WdShing Wood Shingles
Exterior2nd: Exterior covering on house (if more than one material)
AsbShng Asbestos Shingles
AsphShn Asphalt Shingles
BrkComm Brick Common
BrkFace Brick Face
CBlock Cinder Block
CemntBd Cement Board
HdBoard Hard Board
ImStucc Imitation Stucco
MetalSd Metal Siding
Other Other
Plywood Plywood
PreCast PreCast
Stone Stone
Stucco Stucco
VinylSd Vinyl Siding
Wd Sdng Wood Siding
WdShing Wood Shingles
MasVnrType: Masonry veneer type
BrkCmn Brick Common
BrkFace Brick Face
CBlock Cinder Block
None None
Stone Stone
MasVnrArea: Masonry veneer area in square feet
ExterQual: Evaluates the quality of the material on the exterior
Ex Excellent
Gd Good
TA Average/Typical
Fa Fair
Po Poor
ExterCond: Evaluates the present condition of the material on the exterior
Ex Excellent
Gd Good
TA Average/Typical
Fa Fair
Po Poor
Foundation: Type of foundation
BrkTil Brick & Tile
CBlock Cinder Block
PConc Poured Contrete
Slab Slab
Stone Stone
Wood Wood
BsmtQual: Evaluates the height of the basement
Ex Excellent (100+ inches)
Gd Good (90-99 inches)
TA Typical (80-89 inches)
Fa Fair (70-79 inches)
Po Poor (<70 inches
NA No Basement
BsmtCond: Evaluates the general condition of the basement
Ex Excellent
Gd Good
TA Typical - slight dampness allowed
Fa Fair - dampness or some cracking or settling
Po Poor - Severe cracking, settling, or wetness
NA No Basement
BsmtExposure: Refers to walkout or garden level walls
Gd Good Exposure
Av Average Exposure (split levels or foyers typically score average or above)
Mn Mimimum Exposure
No No Exposure
NA No Basement
BsmtFinType1: Rating of basement finished area
GLQ Good Living Quarters
ALQ Average Living Quarters
BLQ Below Average Living Quarters
Rec Average Rec Room
LwQ Low Quality
Unf Unfinshed
NA No Basement
BsmtFinSF1: Type 1 finished square feet
BsmtFinType2: Rating of basement finished area (if multiple types)
GLQ Good Living Quarters
ALQ Average Living Quarters
BLQ Below Average Living Quarters
Rec Average Rec Room
LwQ Low Quality
Unf Unfinshed
NA No Basement
BsmtFinSF2: Type 2 finished square feet
BsmtUnfSF: Unfinished square feet of basement area
TotalBsmtSF: Total square feet of basement area
Heating: Type of heating
Floor Floor Furnace
GasA Gas forced warm air furnace
GasW Gas hot water or steam heat
Grav Gravity furnace
OthW Hot water or steam heat other than gas
Wall Wall furnace
HeatingQC: Heating quality and condition
Ex Excellent
Gd Good
TA Average/Typical
Fa Fair
Po Poor
CentralAir: Central air conditioning
N No
Y Yes
Electrical: Electrical system
SBrkr Standard Circuit Breakers & Romex
FuseA Fuse Box over 60 AMP and all Romex wiring (Average)
FuseF 60 AMP Fuse Box and mostly Romex wiring (Fair)
FuseP 60 AMP Fuse Box and mostly knob & tube wiring (poor)
Mix Mixed
1stFlrSF: First Floor square feet
2ndFlrSF: Second floor square feet
LowQualFinSF: Low quality finished square feet (all floors)
GrLivArea: Above grade (ground) living area square feet
BsmtFullBath: Basement full bathrooms
BsmtHalfBath: Basement half bathrooms
FullBath: Full bathrooms above grade
HalfBath: Half baths above grade
Bedroom: Bedrooms above grade (does NOT include basement bedrooms)
Kitchen: Kitchens above grade
KitchenQual: Kitchen quality
Ex Excellent
Gd Good
TA Typical/Average
Fa Fair
Po Poor
TotRmsAbvGrd: Total rooms above grade (does not include bathrooms)
Functional: Home functionality (Assume typical unless deductions are warranted)
Typ Typical Functionality
Min1 Minor Deductions 1
Min2 Minor Deductions 2
Mod Moderate Deductions
Maj1 Major Deductions 1
Maj2 Major Deductions 2
Sev Severely Damaged
Sal Salvage only
Fireplaces: Number of fireplaces
FireplaceQu: Fireplace quality
Ex Excellent - Exceptional Masonry Fireplace
Gd Good - Masonry Fireplace in main level
TA Average - Prefabricated Fireplace in main living area or Masonry Fireplace in basement
Fa Fair - Prefabricated Fireplace in basement
Po Poor - Ben Franklin Stove
NA No Fireplace
GarageType: Garage location
2Types More than one type of garage
Attchd Attached to home
Basment Basement Garage
BuiltIn Built-In (Garage part of house - typically has room above garage)
CarPort Car Port
Detchd Detached from home
NA No Garage
GarageYrBlt: Year garage was built
GarageFinish: Interior finish of the garage
Fin Finished
RFn Rough Finished
Unf Unfinished
NA No Garage
GarageCars: Size of garage in car capacity
GarageArea: Size of garage in square feet
GarageQual: Garage quality
Ex Excellent
Gd Good
TA Typical/Average
Fa Fair
Po Poor
NA No Garage
GarageCond: Garage condition
Ex Excellent
Gd Good
TA Typical/Average
Fa Fair
Po Poor
NA No Garage
PavedDrive: Paved driveway
Y Paved
P Partial Pavement
N Dirt/Gravel
WoodDeckSF: Wood deck area in square feet
OpenPorchSF: Open porch area in square feet
EnclosedPorch: Enclosed porch area in square feet
3SsnPorch: Three season porch area in square feet
ScreenPorch: Screen porch area in square feet
PoolArea: Pool area in square feet
PoolQC: Pool quality
Ex Excellent
Gd Good
TA Average/Typical
Fa Fair
NA No Pool
Fence: Fence quality
GdPrv Good Privacy
MnPrv Minimum Privacy
GdWo Good Wood
MnWw Minimum Wood/Wire
NA No Fence
MiscFeature: Miscellaneous feature not covered in other categories
Elev Elevator
Gar2 2nd Garage (if not described in garage section)
Othr Other
Shed Shed (over 100 SF)
TenC Tennis Court
NA None
MiscVal: $Value of miscellaneous feature
MoSold: Month Sold (MM)
YrSold: Year Sold (YYYY)
SaleType: Type of sale
WD Warranty Deed - Conventional
CWD Warranty Deed - Cash
VWD Warranty Deed - VA Loan
New Home just constructed and sold
COD Court Officer Deed/Estate
Con Contract 15% Down payment regular terms
ConLw Contract Low Down payment and low interest
ConLI Contract Low Interest
ConLD Contract Low Down
Oth Other
SaleCondition: Condition of sale
Normal Normal Sale
Abnorml Abnormal Sale - trade, foreclosure, short sale
AdjLand Adjoining Land Purchase
Alloca Allocation - two linked properties with separate deeds, typically condo with a garage unit
Family Sale between family members
Partial Home was not completed when last assessed (associated with New Homes)
Downloaded from openml.org.
Understanding the data
What does TotRmsAbvGrd refer to?
Solution
TotRmsAbvGrd: Total rooms above grade (does not include bathrooms)
Variable Classes
How many variables are numeric?
Solution
36 numeric (are these all continuous or discrete?) 43 categorical (are these all categorical or ordinate ?)
Where’s All The Nans?
How many Nan entries are there per variable?
Solution
df.isna().sum().sort_values(ascending=False).head(20)OUTPUT_START
|column|count| |—|—| |PoolQC |1453| MiscFeature | 1406 Alley | 1369 Fence | 1179 FireplaceQu | 690 LotFrontage |259 GarageYrBlt |81 GarageCond |81 GarageType |81 GarageFinish |81 GarageQual |81 BsmtExposure |38 BsmtFinType2 |38 BsmtCond |37 BsmtQual |37 BsmtFinType1 |37 MasVnrArea | 8 MasVnrType | 8 Electrical | 1 MSSubClass | 0 dtype: int64
OUTPUT_END
EXERCISE_START
Which of these variables could be the best predictor of house sale price? Why?
Solution
Possible answers: SquareFt, OverallQual, YearBuilt They intutively are going to be corrleated with SalePrice - but NB: also with each other!
Target Feature: SalePrice
# add target variable 'sales price' to data df from housing object
df[housing.target_names[0]] = housing.target.tolist()
df.describe()
| MSSubClass | LotFrontage | LotArea | OverallQual | OverallCond | YearBuilt | YearRemodAdd | MasVnrArea | BsmtFinSF1 | BsmtFinSF2 | ... | WoodDeckSF | OpenPorchSF | EnclosedPorch | 3SsnPorch | ScreenPorch | PoolArea | MiscVal | MoSold | YrSold | SalePrice | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| count | 1460.000000 | 1201.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1452.000000 | 1460.000000 | 1460.000000 | ... | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 |
| mean | 56.897260 | 70.049958 | 10516.828082 | 6.099315 | 5.575342 | 1971.267808 | 1984.865753 | 103.685262 | 443.639726 | 46.549315 | ... | 94.244521 | 46.660274 | 21.954110 | 3.409589 | 15.060959 | 2.758904 | 43.489041 | 6.321918 | 2007.815753 | 180921.195890 |
| std | 42.300571 | 24.284752 | 9981.264932 | 1.382997 | 1.112799 | 30.202904 | 20.645407 | 181.066207 | 456.098091 | 161.319273 | ... | 125.338794 | 66.256028 | 61.119149 | 29.317331 | 55.757415 | 40.177307 | 496.123024 | 2.703626 | 1.328095 | 79442.502883 |
| min | 20.000000 | 21.000000 | 1300.000000 | 1.000000 | 1.000000 | 1872.000000 | 1950.000000 | 0.000000 | 0.000000 | 0.000000 | ... | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 1.000000 | 2006.000000 | 34900.000000 |
| 25% | 20.000000 | 59.000000 | 7553.500000 | 5.000000 | 5.000000 | 1954.000000 | 1967.000000 | 0.000000 | 0.000000 | 0.000000 | ... | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 5.000000 | 2007.000000 | 129975.000000 |
| 50% | 50.000000 | 69.000000 | 9478.500000 | 6.000000 | 5.000000 | 1973.000000 | 1994.000000 | 0.000000 | 383.500000 | 0.000000 | ... | 0.000000 | 25.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 6.000000 | 2008.000000 | 163000.000000 |
| 75% | 70.000000 | 80.000000 | 11601.500000 | 7.000000 | 6.000000 | 2000.000000 | 2004.000000 | 166.000000 | 712.250000 | 0.000000 | ... | 168.000000 | 68.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 8.000000 | 2009.000000 | 214000.000000 |
| max | 190.000000 | 313.000000 | 215245.000000 | 10.000000 | 9.000000 | 2010.000000 | 2010.000000 | 1600.000000 | 5644.000000 | 1474.000000 | ... | 857.000000 | 547.000000 | 552.000000 | 508.000000 | 480.000000 | 738.000000 | 15500.000000 | 12.000000 | 2010.000000 | 755000.000000 |
8 rows × 37 columns
what does SalePrice look like?
import helper_functions
helper_functions.plot_salesprice(
df,
# ylog=True
)
Is this a normal distribution? Will that distribution influcence modelling this value? How?
Log Sales price
import numpy as np
import helper_functions
# convert to normal
df['SalePrice'] = np.log(df['SalePrice'].tolist())
helper_functions.plot_salesprice(
df,
# ylog=True
)
Use All Features - One-hot encode Categorical Variables
# Original DataFrame dimensions (+ SalesPrice)
print(f"{df.shape=}")
df.shape=(1460, 80)
# one hot encode categorical variables
import pandas as pd
numeric_variables = df.describe().columns.tolist()
nominative_variables = [x for x in df.columns.tolist() if x not in numeric_variables]
dummy_df = pd.get_dummies(df[nominative_variables])
print(dummy_df.shape)
dummy_df
(1460, 252)
| MSZoning_'C (all)' | MSZoning_FV | MSZoning_RH | MSZoning_RL | MSZoning_RM | Street_Grvl | Street_Pave | Alley_Grvl | Alley_Pave | LotShape_IR1 | ... | SaleType_ConLw | SaleType_New | SaleType_Oth | SaleType_WD | SaleCondition_Abnorml | SaleCondition_AdjLand | SaleCondition_Alloca | SaleCondition_Family | SaleCondition_Normal | SaleCondition_Partial | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Id | |||||||||||||||||||||
| 1 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 2 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 3 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 4 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | ... | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
| 5 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... |
| 1456 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 1457 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 1458 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 1459 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 1460 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
1460 rows × 252 columns
# merge one-hot encoded columns with numeric columns
model_df = pd.concat([df[numeric_variables], dummy_df], axis=1) #.drop('SalePrice', axis=1)
# how many total coulmns now?
print(model_df.shape)
model_df
(1460, 289)
| MSSubClass | LotFrontage | LotArea | OverallQual | OverallCond | YearBuilt | YearRemodAdd | MasVnrArea | BsmtFinSF1 | BsmtFinSF2 | ... | SaleType_ConLw | SaleType_New | SaleType_Oth | SaleType_WD | SaleCondition_Abnorml | SaleCondition_AdjLand | SaleCondition_Alloca | SaleCondition_Family | SaleCondition_Normal | SaleCondition_Partial | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Id | |||||||||||||||||||||
| 1 | 60 | 65.0 | 8450 | 7 | 5 | 2003 | 2003 | 196.0 | 706 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 2 | 20 | 80.0 | 9600 | 6 | 8 | 1976 | 1976 | 0.0 | 978 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 3 | 60 | 68.0 | 11250 | 7 | 5 | 2001 | 2002 | 162.0 | 486 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 4 | 70 | 60.0 | 9550 | 7 | 5 | 1915 | 1970 | 0.0 | 216 | 0 | ... | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
| 5 | 60 | 84.0 | 14260 | 8 | 5 | 2000 | 2000 | 350.0 | 655 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... |
| 1456 | 60 | 62.0 | 7917 | 6 | 5 | 1999 | 2000 | 0.0 | 0 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 1457 | 20 | 85.0 | 13175 | 6 | 6 | 1978 | 1988 | 119.0 | 790 | 163 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 1458 | 70 | 66.0 | 9042 | 7 | 9 | 1941 | 2006 | 0.0 | 275 | 0 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 1459 | 20 | 68.0 | 9717 | 5 | 6 | 1950 | 1996 | 0.0 | 49 | 1029 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 1460 | 20 | 75.0 | 9937 | 5 | 6 | 1965 | 1965 | 0.0 | 830 | 290 | ... | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
1460 rows × 289 columns
# How many numerical columns now?
model_df.describe()
| MSSubClass | LotFrontage | LotArea | OverallQual | OverallCond | YearBuilt | YearRemodAdd | MasVnrArea | BsmtFinSF1 | BsmtFinSF2 | ... | SaleType_ConLw | SaleType_New | SaleType_Oth | SaleType_WD | SaleCondition_Abnorml | SaleCondition_AdjLand | SaleCondition_Alloca | SaleCondition_Family | SaleCondition_Normal | SaleCondition_Partial | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| count | 1460.000000 | 1201.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1452.000000 | 1460.000000 | 1460.000000 | ... | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 | 1460.000000 |
| mean | 56.897260 | 70.049958 | 10516.828082 | 6.099315 | 5.575342 | 1971.267808 | 1984.865753 | 103.685262 | 443.639726 | 46.549315 | ... | 0.003425 | 0.083562 | 0.002055 | 0.867808 | 0.069178 | 0.002740 | 0.008219 | 0.013699 | 0.820548 | 0.085616 |
| std | 42.300571 | 24.284752 | 9981.264932 | 1.382997 | 1.112799 | 30.202904 | 20.645407 | 181.066207 | 456.098091 | 161.319273 | ... | 0.058440 | 0.276824 | 0.045299 | 0.338815 | 0.253844 | 0.052289 | 0.090317 | 0.116277 | 0.383862 | 0.279893 |
| min | 20.000000 | 21.000000 | 1300.000000 | 1.000000 | 1.000000 | 1872.000000 | 1950.000000 | 0.000000 | 0.000000 | 0.000000 | ... | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 |
| 25% | 20.000000 | 59.000000 | 7553.500000 | 5.000000 | 5.000000 | 1954.000000 | 1967.000000 | 0.000000 | 0.000000 | 0.000000 | ... | 0.000000 | 0.000000 | 0.000000 | 1.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 1.000000 | 0.000000 |
| 50% | 50.000000 | 69.000000 | 9478.500000 | 6.000000 | 5.000000 | 1973.000000 | 1994.000000 | 0.000000 | 383.500000 | 0.000000 | ... | 0.000000 | 0.000000 | 0.000000 | 1.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 1.000000 | 0.000000 |
| 75% | 70.000000 | 80.000000 | 11601.500000 | 7.000000 | 6.000000 | 2000.000000 | 2004.000000 | 166.000000 | 712.250000 | 0.000000 | ... | 0.000000 | 0.000000 | 0.000000 | 1.000000 | 0.000000 | 0.000000 | 0.000000 | 0.000000 | 1.000000 | 0.000000 |
| max | 190.000000 | 313.000000 | 215245.000000 | 10.000000 | 9.000000 | 2010.000000 | 2010.000000 | 1600.000000 | 5644.000000 | 1474.000000 | ... | 1.000000 | 1.000000 | 1.000000 | 1.000000 | 1.000000 | 1.000000 | 1.000000 | 1.000000 | 1.000000 | 1.000000 |
8 rows × 289 columns
Modelling Dataset Description
- how many observations are there in our dataset?
- how many features are there in the whole dataset?
- how many numerical features are there in the whole dataset?
Solution
- 1460 observations (len(df))
- 79 features total (len(df.columns.tolist())) - 1 (can’t use SalesPrice)
- 36 numerical features (len(df[num_cols].columns.tolist()) - 1 (can’t use SalesPrice)
Modelling Feature Selection
- Can all of those features be used in a model?
- Would you want to use all of those features?
Solution
- yes all the features could be used. With possible implications for the quality of the model.
- features that are not (anti)correlated with the target variable may not add any useful information to the model
- features that are correlated with other features may not add a lot more information and may produce a poorer quality model.
Model Feature Count
- how many features should be used total?
Solution
A possible approach:
- n = number of observations
- uncorrelated features count = (n - 1)
- as correlation increases, feature count proportional to sqrt(n)
- assuming some correlation: sqrt(1460) = 38.21 per: Optimal number of features as a function of sample size for various classification rules
Data analysis and modeling can be very emprical
You need to try things out to see what works. If your features are indepent and identically distributed, or not, will impact how many observations are required
Generally for a classifcation model
- Distribution of features per target class matters a ton
- More observations mean you can use more features
Overfitting
What is model overfitting? how does a model become overfit?
Solution
your model is unabel to generalize - it has ‘memorized’ the data, rather than the patterns in it.
TODO: ADD IN HERE.
EXERCISE_END
Model Feature Quality
- which features should be used to predict the target variable? (which variables are good predictors?)
Solution
Many possible answers here, some general ideas
- those that are most correlated with the target variable
- those that are not correlated with each other
Build regression model to predict sales price
Plot correlations and histograms of those columns
Reminder:
- What features should go in a model to predict high house price?
- What features are correlated with high house price?
Remove nulls from features
# which columns have the most nulls
model_df.isnull().sum().sort_values(ascending=False).head(5)
LotFrontage 259
GarageYrBlt 81
MasVnrArea 8
MSSubClass 0
BsmtExposure_Av 0
dtype: int64
# assume null means none - replace all nulls with zeros for lotFrontage and MasVnrArea
no_null_model_df = model_df
no_null_model_df['LotFrontage'] = no_null_model_df['LotFrontage'].fillna(0)
no_null_model_df['MasVnrArea'] = no_null_model_df['MasVnrArea'].fillna(0)
# GarageYrBlt 0 makes no sense - replace with mean
no_null_model_df['GarageYrBlt'] = no_null_model_df['GarageYrBlt'].fillna(no_null_model_df['GarageYrBlt'].mean())
no_null_model_df.isnull().sum().sort_values(ascending=False).head(5)
MSSubClass 0
Exterior1st_Stucco 0
BsmtFinType1_GLQ 0
BsmtFinType1_BLQ 0
BsmtFinType1_ALQ 0
dtype: int64
separate features from target
# define features and target
features = no_null_model_df.drop('SalePrice', axis=1)
features
target = no_null_model_df['SalePrice']
# confirm features do not contain target
[x for x in features.columns if x == 'SalePrice']
[]
Establish Model Performance Baseline
How well does always guessing the mean do in terms of RMSE?
from math import sqrt
mean_sale_price = model_df.SalePrice.mean()
print(f"{mean_sale_price=:.2f}")
diffs = model_df.SalePrice - mean_sale_price
rse = (diffs * diffs).apply(sqrt)
baseline_rmse = rse.mean()
print(f'baseline rmse: {baseline_rmse:.2f}')
mean_sale_price=12.02
baseline rmse: 0.31
Define function to fit and assess a Linear model
from collections import defaultdict
from sklearn import preprocessing
from sklearn.linear_model import LinearRegression
from sklearn.metrics import mean_squared_error, r2_score
from sklearn.model_selection import train_test_split, KFold
import matplotlib.pyplot as plt
from typing import Tuple
from math import sqrt
import numpy as np
def run_linear_regression_with_kf(features: pd.DataFrame, labels: pd.Series,
n_splits=5, title='logistic regression model'
) -> Tuple[float,float,float,float]:
"""
scale, split, and model data. Return model performance statistics, plot confusion matrix
feature: dataframe of feature columns to model
labels: series of labels to model against
test_size: fraction of labels to use in test split
title: title for chart
return: recall mean, recall sd, precision mean, precision sd
"""
# set up splits/folds and array for stats.
kf = KFold(n_splits=n_splits)
r2s = np.zeros(n_splits)
rmses = np.zeros(n_splits)
train_rmses = np.zeros(n_splits)
# fit model for each split/fold
for i, (train_idx, test_idx) in enumerate(kf.split(X=features, y=labels)):
# split features data for dataframes
try:
X_train = features.iloc[train_idx]
y_train = labels.iloc[train_idx]
X_test = features.iloc[test_idx]
y_test = labels.iloc[test_idx]
# or split features data for ndarrays (pca transformed features)
except AttributeError:
X_train = features[train_idx]
y_train = labels.iloc[train_idx]
X_test = features[test_idx]
y_test = labels.iloc[test_idx]
# scale all features to training features
scaler = preprocessing.StandardScaler().fit(X_train)
X_train = scaler.transform(X_train)
X_test = scaler.transform(X_test)
# fit model, evaluate
regr = LinearRegression().fit(X_train, y_train)
y_pred = regr.predict(X_test)
r2s[i] = r2_score(y_test, y_pred)
rmses[i] = sqrt(mean_squared_error(y_test, y_pred))
y_pred_train = regr.predict(X_train)
train_rmses[i] = sqrt(mean_squared_error(y_train, y_pred_train))
r2_mean = r2s.mean()
r2_sd = r2s.std()
rmse_mean = rmses.mean()
rmse_sd = rmses.std()
train_rmse_mean = train_rmses.mean()
train_rmse_sd = train_rmses.std()
# plot y_true vs y_pred
fig, ax = plt.subplots(1, 1, figsize=(6, 6))
ax.scatter(y_test, y_pred, alpha=0.3)
ax.set_title(f'{title}\n' \
'mean r2: {:.2f},\n'\
'mean rmse {:.2f}'
.format(r2_mean, rmse_mean)
)
ax.set_xlabel('True Value')
ax.set_ylabel('Predicted Value')
stats = (r2_mean, rmse_mean, r2_sd, rmse_sd)
train_test_errors = (rmse_mean, rmse_sd, train_rmse_mean, train_rmse_sd)
model_data_and_pred = (regr, X_train, y_train, X_test, y_test, y_pred)
fig_and_ax = (fig, ax)
return stats, train_test_errors, model_data_and_pred, fig_and_ax
fit a linear model with all features
# set kfold splits
n_splits = 3
# keep all model stats in one dict
all_stats = {}
#r2_mean, rmse_mean, r2_sd, rmse_sd, regr, fig, ax =
plt.ion()
stats, train_test_errors, model_data_and_pred, fig_and_ax = run_linear_regression_with_kf(features=features, labels=target, n_splits=n_splits, title='all features')
all_stats['all'] = stats
model has difficulty inferring with several very large outliers
# plot ignoring outliers
fig, ax = fig_and_ax
ax.set_ylim(10.5, 14)
fig
Overfitting - bias and variance
# the model is overfit
rmse_mean, rmse_sd, train_rmse_mean, train_rmse_sd = train_test_errors
print(f'test rmse ± sd: \t {rmse_mean} ± {rmse_sd}')
print(f'train rmse ± sd:\t {train_rmse_mean} ± {train_rmse_sd}')
test rmse ± sd: 27282372629.48491 ± 28180380572.225414
train rmse ± sd: 0.08863829483269596 ± 0.00626317568881641
PCA all features to 100 dimensions
from sklearn.decomposition import PCA
n_components = 100
p = PCA(n_components=n_components )
features_pca = p.fit_transform(features)
stats, train_test_errors, model_data_and_pred, fig_and_ax = run_linear_regression_with_kf(features=features_pca, labels=target,
title=f'{n_components} Princpal Components', n_splits=n_splits)
all_stats['all_pca'] = stats
# fewer dimensions - higher bias error?
overfitting?
# the model is NOT overfit
rmse_mean, rmse_sd, train_rmse_mean, train_rmse_sd = train_test_errors
print(f'test rmse ± sd: \t {rmse_mean} ± {rmse_sd}')
print(f'train rmse ± sd:\t {train_rmse_mean} ± {train_rmse_sd}')
test rmse ± sd: 0.14793978100161198 ± 0.012474628694285275
train rmse ± sd: 0.12223878649819635 ± 0.005870162810591587
Model Comparison
# create combined stats df
stats_df = pd.DataFrame.from_dict(all_stats).set_index(
pd.Index(['r2_mean', 'rmse_mean', 'r2_sd', 'rmse_sd'], name='statistics')
)
# plot figures
fig, axs = plt.subplots(1, 2, figsize=(10, 5))
stats_df.loc['r2_mean'].plot(ax=axs[0], kind='bar', yerr=stats_df.loc['r2_sd'], title='mean r2', color='lightblue', ylim=(-stats_df.loc['r2_mean']['all_pca']/2, stats_df.loc['r2_mean']['all_pca']*2))
stats_df.loc['rmse_mean'].plot(ax=axs[1], kind='bar', yerr=stats_df.loc['rmse_sd'], title=f'mean RMSE', color='orange', ylim=(0, stats_df.loc['rmse_mean']['all_pca']*3))
# plot baseline - guess mean every time RMSE
xmin, xmax = plt.xlim()
axs[1].hlines(baseline_rmse, xmin=xmin, xmax=xmax)
axs[1].text(xmax/3, baseline_rmse + baseline_rmse*0.05, 'Baseline RMSE')
# title and show
plt.suptitle(f'model statistics\nerrbars=sd n={n_splits}')
plt.show()
Fit a PCA model with fewer dimensions.
What do you think the out come will be?
Solution
upping variables in classifier, reduce bias error. tail ends of distributions can have high predictive power - a small amount of variance can be impactful
What Is Going On?
Intuition:
PCA is a way to rotate the axes of your dataset around the data so that the axes line up with the directions of the greatest variation through the data.
reviewed
- exlpored Ames housing dataset
- looked for variables that would correlate with/be good predictors for housing prices
- indicated that PCA might be a way to approach this problem
We’ll go into more detail on PCA in the next episode
Key Points