def split_train_test(X, Y, trs_len=0.80):
    """
    Split both X and Y into train and test sets.

    trs_len - how much data should we use for training?
              by default it's 0.80 meaning 80%, the remining
              20% of the data will be used for testing.
    """
    lx = len(X)
    # 1 year train set - 315 examples,  test - 80.
    # 3 year train set - 1167 examples, test - 294
    trs = int(lx * trs_len) - 1
    train_x, train_y = X[:trs], Y[:trs]
    test_x, test_y = X[trs:], Y[trs:]
    return train_x, train_y, test_x, test_y