def scale_dataframe(train, test, cols, replace=True):
""" Takes train and test dataframes and a list of columns that need to be scaled.
Returns a 3-tuple comprising the scaled dataframes and the fitted scaler.
"""
scaler = StandardScaler()
scaledTrain = pd.DataFrame(data=scaler.fit_transform(train[cols]), columns=cols)
scaledTest = pd.DataFrame(data=scaler.transform(test[cols]), columns=cols)
scaledTrain.columns = scaler.get_feature_names()
scaledTest.columns = scaler.get_feature_names()
scaledTrain.index = train.index
scaledTest.index = test.index
if replace is True:
train = train.drop(cols, axis=1)
train = train.join(scaledTrain)
test = test.drop(cols, axis=1)
test = test.join(scaledTest)
return (train, test, scaler)
