def ft_chunk(data, i, cols, rel=0, *args, **kwargs):
    """Generates a context feature based on chunk annotation in column
    `chunktag`.

    :param data: data
    :type: np.recarray
    :param i: focus position
    :type i: int
    :param cols: column map
    :type cols: dict
    :param rel: relative position of context features
    :type rel: int
    :return: feature
    :rtype: str
    """
    if 0 <= i + rel < len(data):
        chunktag = data[i + rel][cols['chunktag']]
    else:
        chunktag = None
    return 'ch[%s]=%s' % (rel, chunktag)
