max/min/max_by/min_by functions should support strings

[jamesls]

I think the current inconsistently is confusing with sort/sort_by. You can sort/sortby with arrays of strings, but not with the min/max_ functions. I'd propose updating the spec to support strings:

# Works
>>> jmespath.search('sort(@)', ['b', 'a', 'd', 'c'])
['a', 'b', 'c', 'd']

# Fails
>>> jmespath.search('max(@)', ['b', 'a', 'd', 'c'])
jmespath.exceptions.JMESPathTypeError: In function max(), invalid type for value: b, expected one of: ['array-number'], received: "str"

cc @mtdowling

[mtdowling]

Can you provide more information on how values are compared? For example, PHP's max function lays out exactly how values are compared when they're mixed: http://php.net/manual/en/function.max.php

[jamesls]

It wouldn't compare mixed values. The intent here was to bring parity to sort/min/max and sort_by/min_by/max_by. Currently sort* supports an array of numbers or an array of strings. The min/max should have the same behavior. Trying to mix types should have the same behavior as sort/sort_by which results in an error.