CODE EXAMPLE FOR PYTHON

DataConversionWarning: A column-vector y was passed when a 1d array was expected. Please change the shape of y to (n_samples, ), for example using ravel(). y = column_or_1d(y, warn=True)

model = forest.fit(train_fold, train_y.values.ravel())

Explanation:

.values will give the values in a numpy array (shape: (n,1))

.ravel will convert that array shape to (n, ) (i.e. flatten it)