Wrapper for test_train_split to produce train, validation, and test splits for any number of input arrays

What is the right way to build wrappers around the test_train_split function with *args and **kwargs? To give more context, data science often require to create a test-validate-train split, so I thought to build a wrapper like

def train_validate_test_split(*dataframe, **options):
   train, test = train_test_split(dataframe, options)
   train, val = train_test_split(train, options)
   return train, val, test

that gives a train, validation, test split of the dataset from oneliner calls. However, executing

train_validate_test_split(dataframe_1, test_size = 0.2)

leads to a catastrophic failure. I guess that I am messing *args and **kwargs quite spectacularly, but I still have problems in putting my head around them. Any suggestion would be greatly appreciated.

Answer

The function signature is:

train_test_split(*arrays, **options)

meaning it accepts any number of positional arrays and any number of keyword options. To return train, val, test as you wish, one would proceed as follows:

from sklearn.model_selection import train_test_split
df = pd.DataFrame({"x": np.random.randn(1000),"y": np.random.randn(1000)})

def train_validate_test_split(dataframe, **options):
   train, test = train_test_split(dataframe, **options)
   train, val = train_test_split(train, **options)
   return train, val, test

a,b,c = train_validate_test_split(df, train_size=.25)

EDIT

To accept either 1 or 2 inputs use:

def train_val_test_split(*arrays,**options):

    if len(arrays) == 1:
        X_train, X_test = train_test_split(*arrays,**options)
        X_train, X_val = train_test_split(X_train,**options)
        print("Unpack to X_train, X_val, X_test")
        return X_train, X_val, X_test

    if len(arrays) == 2:
        X_train, X_test, y_train, y_test = train_test_split(*arrays,**options)
        X_train, X_val, y_train, y_val = train_test_split(X_train,y_train,**options)
        print("Unpack to X_train, X_val, X_test, y_train, y_val, y_test")
        return X_train, X_val, X_test, y_train, y_val, y_test

    else:
        raise ValueError("Only implemented for 1 or 2 arrays. "
                          f"You provided {len(arrays)} arrays")

or for any number of input arrays:

y = np.random.randn(1000)
def train_val_test_split(*arrays,**options):
    '''
    inputs:
        arrays - any number of array to split,
    outputs:
        sequence 
        arr1_train, arr2_train, ... , arr1_val , arr2_val, ..., arr1_test, arr2_test, ...
    '''
    *out, = train_test_split(*arrays,**options)
    train = out[0::2] #x1_train, x2_train, ...
    test  = out[1::2] #x1_test, x2_test, ...
    *train_val, = train_test_split(*train,**options)
    train = train_val[0::2]
    val   = train_val[1::2]
    print(f"Unpack to {len(arrays)*3} tuples: train,...,val,..., test...")
    return tuple(split for tuple_ in zip(train,val,test) for split in tuple_)

x = train_val_test_split(y,y,y)

for item in x:
    print(item.shape, end=", ")

Unpack to 9 tuples: train,...,val,..., test...
(562,), (188,), (250,), (562,), (188,), (250,), (562,), (188,), (250,),