def get_columns_to_compare(test_folder):
    """
    Helper function to test the files in SampleData. Gets
    indices of angles that can be compared for equality, depending
    on which file is being compared.

    There are 57 angle coordinates to be compared, with 3 coordinates
    for each of 19 angles.

    If the global coordinate system is unknown for a given file,
    angles affected by the GCS are ignored.
    Ignored angles are Pelvis, R Foot, L Foot, Head, Thorax, with corresponding
    indices 0, 1, 2 and 21 - 32.

    The files in Test_Files also ignore the Neck X coordinate, at 
    index 33.
    """
    gcs_ignore = [i for i in range(21, 33)]
    gcs_ignore.extend([0,1,2])
    columns = [i for i in range(57)]
    if (test_folder == 'ROM'):
        return columns
    if (test_folder == '59993_Frame'):
        for i in gcs_ignore:
            columns.remove(i)
        return columns
    if (test_folder == 'Test_Files'):
        for i in gcs_ignore:
            columns.remove(i)
        columns.remove(33)
        return columns