def group_concat(arg, sep=',', where=None):
    """
    Concatenate values using the indicated separator (comma by default) to
    produce a string

    Parameters
    ----------
    arg : array expression
    sep : string, default ','
    where : bool, default None

    Returns
    -------
    concatenated : string scalar
    """
    return ops.GroupConcat(arg, sep, where).to_expr()
Concatenate values using the indicated separator (comma by default) to
    produce a string

    Parameters
    ----------
    arg : array expression
    sep : string, default ','
    where : bool, default None

    Returns
    -------
    concatenated : string scalar