def column2list(matrix: list, column_idx: int) -> list:
    """
    Convert column from features 2D matrix to 1D list of
    that feature.
    :param matrix: 2D square array of number
    :param column_idx: column index in the matrix
    :return:
    """
    if len(matrix) <= 1:
        return matrix if matrix else []

    if column_idx >= len(matrix[0]):
        return [-1]

    new_column = []

    for line in matrix:
        new_column.append(line[column_idx])
    return new_column