'Return an anonymous filter function that will be passed the array
of parsed columns. Return None if no filter function can be
created for the given params.
The function will compare the column at index `column` against `val`
using the given op where op is one of:
- eq: the list `val` exactly matches the list in the column
- has: the list in the column contains the sublist `val`'

def create_list_filter(self, column, op, val):

    if ('eq' == op):
        val = self.parse_value(val, 'list')
        return (lambda d: (d[column] == val))
    elif ('has' == op):
        return (lambda d: (val in d[column]))
    return None
