find_or_check_numerical_variables#

With find_or_check_numerical_variables() you can automatically capture in a list the names of all the variables of type numerical in the dataset.

Let’s create a toy dataset with numerical, categorical and datetime variables:

import pandas as pd
from sklearn.datasets import make_classification

X, y = make_classification(
    n_samples=1000,
    n_features=4,
    n_redundant=1,
    n_clusters_per_class=1,
    weights=[0.50],
    class_sep=2,
    random_state=1,
)

# transform arrays into pandas df and series
colnames = [f"num_var_{i+1}" for i in range(4)]
X = pd.DataFrame(X, columns=colnames)

X["cat_var1"] = ["Hello"] * 1000
X["cat_var2"] = ["Bye"] * 1000

X["date1"] = pd.date_range("2020-02-24", periods=1000, freq="T")
X["date2"] = pd.date_range("2021-09-29", periods=1000, freq="H")
X["date3"] = ["2020-02-24"] * 1000

print(X.head())

We see the resulting dataframe below:

   num_var_1  num_var_2  num_var_3  num_var_4 cat_var1 cat_var2  \
0  -1.558594   1.634123   1.556932   2.869318    Hello      Bye
1   1.499925   1.651008   1.159977   2.510196    Hello      Bye
2   0.277127  -0.263527   0.532159   0.274491    Hello      Bye
3  -1.139190  -1.131193   2.296540   1.189781    Hello      Bye
4  -0.530061  -2.280109   2.469580   0.365617    Hello      Bye

                date1               date2       date3
0 2020-02-24 00:00:00 2021-09-29 00:00:00  2020-02-24
1 2020-02-24 00:01:00 2021-09-29 01:00:00  2020-02-24
2 2020-02-24 00:02:00 2021-09-29 02:00:00  2020-02-24
3 2020-02-24 00:03:00 2021-09-29 03:00:00  2020-02-24
4 2020-02-24 00:04:00 2021-09-29 04:00:00  2020-02-24

We can now use find_or_check_numerical_variables() to capture the names of all numerical variables in a list. So let’s do that and then display the list:

from feature_engine.variable_handling import find_or_check_numerical_variables

var_num = find_or_check_numerical_variables(X)

var_num

We see the names of the variables in the list below:

['num_var_1', 'num_var_2', 'num_var_3', 'num_var_4']

We can also use find_or_check_numerical_variables() with a list of variables. It will corroborate that the variables indicated in the list are of type numeric.

var_num = find_or_check_numerical_variables(X, ['num_var_1', 'num_var_2'])

var_num

In this case, both variables, if numerical, will be in the resulting list:

['num_var_1', 'num_var_2']

If we pass a variable that is not of type numerical, find_or_check_numerical_variables() will return an error:

find_or_check_numerical_variables(X, ['num_var_1', 'cat_var1'])

Below we see the error message:

TypeError: Some of the variables are not numerical. Please cast them as numerical
before using this transformer.