def get_labels_order_2ab(l, a, b):
    """Get all combinations ij, where i,j are feature labels.

    Parameters
    ----------
    x : list
        Length m vector, where m is the number of features.

    Returns
    -------
    new_features : list
        List of new feature names.
    """
    L = len(l)
    new_features = []
    for f1 in range(L):
        for f2 in range(f1, L):
            new_features.append(l[f1] + '_' + str(a) + '_x_' + l[f2] + '_' +
                str(b))
    return new_features
