How to split training and test sets?

Question

Where should we use

X_train,X_test,y_train,y_test= train_test_split(data, test_size=0.3, random_state=42)

and where should we use

train, test= train_test_split(data, test_size=0.3, random_state=0). 

The former one return this:

value error: not enough values to unpack (expected 4, got 2)

Answer 1

The first form you use if you want to split instances with features (X) and labels (y). The second form you use if you only want to split features (X).

X_train, X_test, y_train, y_test= train_test_split(data, y, test_size=0.3, random_state=42)

The reason why it didn' t work for you was because you didn't prodide the label data in your train_test_split() function. The above should work well. Just replace y with your label/target data.

Answer 2

if you have 1 data list, it split to 2,

                             |---data_train
data ----train_test_split()--|
                             |---data_test

if you have 2 data list, it split EACH of the data list to 2, that is 4 in total.

                                       |---data_train_x
                                       |---data_train_y
data_x, data_y ----train_test_split()--|
                                       |---data_test_x
                                       |---data_test_y

The same as n data list.