Stratify split by column (object)

Question

When trying to do a strafied split by a column (categorical) it returns me error.

Country     ColumnA    ColumnB   ColumnC   Label
AB            0.2        0.5       0.1       14  
CD            0.9        0.2       0.6       60
EF            0.4        0.3       0.8       5
FG            0.6        0.9       0.2       15

Here's my code:

X = df.loc[:, df.columns != 'Label']
y = df['Label']

# Train/test split
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.3, random_state=0, stratify=df.Country)

from sklearn.linear_model import LinearRegression
lm = LinearRegression()
lm.fit(X_train,y_train)
lm_predictions = lm.predict(X_test)

So I get error as follows:

ValueError: could not convert string to float: 'AB'

cant reproduce the error (using "Country" for "country_code") — Christian Sloper, Mar 27 '19 at 18:33

mujjiga · Accepted Answer · 2019-03-27T22:33:22.523

from sklearn.model_selection import train_test_split
from sklearn.linear_model import LinearRegression

df = pd.DataFrame({
        'Country': ['AB', 'CD', 'EF', 'FG']*20,
        'ColumnA' : [1]*20*4,'ColumnB' : [10]*20*4, 'Label': [1,0,1,0]*20
    })

df['Country_Code'] = df['Country'].astype('category').cat.codes

X = df.loc[:, df.columns.drop(['Label','Country'])]
y = df['Label']
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.3, random_state=0, stratify=df.Country_Code)
lm = LinearRegression()
lm.fit(X_train,y_train)
lm_predictions = lm.predict(X_test)

Convert the string values in country to numbers and save it as a new column
When creating x train data drop label (y) and also the string country columns

Method 2

If your test data on which you will make predictions will come later, you will need a mechanism to convert their country into code before making predictions. The recommended way in such a cases is to use LabelEncoder on which you can use fit method to encode strings to labels and later use transform to encode the country of test data.

from sklearn.model_selection import train_test_split
from sklearn.linear_model import LinearRegression
from sklearn import preprocessing

df = pd.DataFrame({
        'Country': ['AB', 'CD', 'EF', 'FG']*20,
        'ColumnA' : [1]*20*4,'ColumnB' : [10]*20*4, 'Label': [1,0,1,0]*20
    })

# Train-Validation 
le = preprocessing.LabelEncoder()
df['Country_Code'] = le.fit_transform(df['Country'])
X = df.loc[:, df.columns.drop(['Label','Country'])]
y = df['Label']
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.3, random_state=0, stratify=df.Country_Code)
lm = LinearRegression()
lm.fit(X_train,y_train)

# Test
test_df = pd.DataFrame({'Country': ['AB'], 'ColumnA' : [1],'ColumnB' : [10] })
test_df['Country_Code'] = le.transform(test_df['Country'])
print (lm.predict(test_df.loc[:, test_df.columns.drop(['Country'])]))

score 0 · Answer 2 · answered Mar 27 '19 at 22:09

In reproducing your code, I found that the error comes from trying to fit a linear regression model on a set of features that includes strings. This answer gives you some options for what to do. I would suggest using X_train, X_test = pd.get_dummies(X_train.Country), pd.get_dummies(X_test.Country) to one-hot encode your countries after you make your train_test_split() to preserve the class balance that you are looking for.

Stratify split by column (object)

2 Answers2

Method 2