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Model Selection

How To Calculate r^2 with scikit-learn

This tutorial explains how to calculate r^2 from scikit-learn on a regression model from catboost.

During this tutorial you will build and evaluate a model to predict arrival delay for flights in and out of NYC in 2013.

Packages

This tutorial uses:

Open a new Jupyter notebook and import the following:


import statsmodels.api as sm
import pandas as pd
import numpy as np
from sklearn.metrics import r2_score
from sklearn.model_selection import train_test_split

from catboost import CatBoostRegressor, Pool

Reading the data

The data is from rdatasets imported using the Python package statsmodels.


df = sm.datasets.get_rdataset('flights', 'nycflights13').data
df.info()


RangeIndex: 336776 entries, 0 to 336775
Data columns (total 19 columns):
 #   Column          Non-Null Count   Dtype  
---  ------          --------------   -----  
 0   year            336776 non-null  int64  
 1   month           336776 non-null  int64  
 2   day             336776 non-null  int64  
 3   dep_time        328521 non-null  float64
 4   sched_dep_time  336776 non-null  int64  
 5   dep_delay       328521 non-null  float64
 6   arr_time        328063 non-null  float64
 7   sched_arr_time  336776 non-null  int64  
 8   arr_delay       327346 non-null  float64
 9   carrier         336776 non-null  object 
 10  flight          336776 non-null  int64  
 11  tailnum         334264 non-null  object 
 12  origin          336776 non-null  object 
 13  dest            336776 non-null  object 
 14  air_time        327346 non-null  float64
 15  distance        336776 non-null  int64  
 16  hour            336776 non-null  int64  
 17  minute          336776 non-null  int64  
 18  time_hour       336776 non-null  object 
dtypes: float64(5), int64(9), object(5)
memory usage: 48.8+ MB

Feature Engineering

Handle null values


df.isnull().sum()

year                 0
month                0
day                  0
dep_time          8255
sched_dep_time       0
dep_delay         8255
arr_time          8713
sched_arr_time       0
arr_delay         9430
carrier              0
flight               0
tailnum           2512
origin               0
dest                 0
air_time          9430
distance             0
hour                 0
minute               0
time_hour            0
dtype: int64

As this model will predict arrival delay, the Null values are caused by flights did were cancelled or diverted. These can be excluded from this analysis.


df.dropna(inplace=True)

Convert the times from floats or ints to hour and minutes


df['arr_hour'] = df.arr_time.apply(lambda x: int(np.floor(x/100)))
df['arr_minute'] = df.arr_time.apply(lambda x: int(x - np.floor(x/100)*100))
df['sched_arr_hour'] = df.sched_arr_time.apply(lambda x: int(np.floor(x/100)))
df['sched_arr_minute'] = df.sched_arr_time.apply(lambda x: int(x - np.floor(x/100)*100))
df['sched_dep_hour'] = df.sched_dep_time.apply(lambda x: int(np.floor(x/100)))
df['sched_dep_minute'] = df.sched_dep_time.apply(lambda x: int(x - np.floor(x/100)*100))
df.rename(columns={'hour': 'dep_hour',
                   'minute': 'dep_minute'}, inplace=True)
                   

Prepare data for modeling

Set up train-test split


target = 'arr_delay'
y = df[target]
X = df.drop(columns=[target, 'flight', 'tailnum', 'time_hour', 'year', 'dep_time', 'sched_dep_time', 'arr_time', 'sched_arr_time', 'dep_delay'])
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=.2, random_state=1066)

Fit the model

Build the regression model


categorical_features = X_train.select_dtypes(exclude=[np.number])

train_pool = Pool(X_train, y_train, categorical_features)
test_pool = Pool(X_test, y_test, categorical_features)

model = CatBoostRegressor(iterations=500, max_depth=5, learning_rate=0.05, random_seed=1066, logging_level='Silent')
model.fit(X_train, y_train, eval_set=test_pool, cat_features=categorical_features, use_best_model=True, early_stopping_rounds=10)


Using r2_score from scikit-learn, calculate the r^2.


r2 = r2_score(y_test, model.predict(X_test))
r2

0.9418282555971598
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