Unexpected behavior of KeyTake

Question

list = {{a, b, c, e}, {1, 2, b, h}, {"a", "h", 3, 5}};
asso = GroupBy[list, {#[[1]], #[[2]]} &]

<|{a, b} -> {{a, b, c, e}}, 
  {1, 2} -> {{1, 2, b, h}}, 
  {"a","h"} -> {{"a", "h", 3, 5}}|>

There is a problem in this code, since "a" and "h" might be two keys. However, KeyExistsQ is not Listable, but KeyTake is.

KeyExistsQ[asso, {"a", "h"}]

True

KeyTake[asso, {"a", "h"}]

<||>

So I wrap Key around {"a", "h"} to eliminate ambiguity.

KeyTake[asso, Key[{"a", "h"}]]

<||>

Contrast the above with

KeyDrop[asso, Key[{"a", "h"}]]

<|{a, b} -> {{a, b, c, e}}, {1, 2} -> {{1, 2, b, h}}|>

Have I found a bug? Tested on V10.4

Answer 1

The behavioral discrepancy can be shown with a very simple example.

assoc = <|1 -> 1, 2 -> 2|>;
{KeyTake[assoc, 1], KeyTake[assoc, Key[1]], KeyTake[assoc, Key[1][assoc]]}

{<|1 -> 1|>, <||>, <|1 -> 1|>}

{KeyDrop[assoc, 1], KeyDrop[assoc, Key[1]], KeyDrop[assoc, Key[1][assoc]]}

{<|2 -> 2|>, <|2 -> 2|>, <|2 -> 2|>}

Surely the behavior of KeyTake[assoc, Key[1]] and KeyDrop[assoc, Key[1]] should be more consistent. Personally, I feel it is the behavior of KeyDrop that is wrong.

Update

I reported this issue to Wolfram tech support. Yesterday, 2016-Jul-7, I received a reply from which I quote the relevant section.

It does appear that KeyDrop is not behaving consistently. I have forwarded an incident report to our developers with the information you provided. If I receive any progress on this issue, you will be posted regarding the same.

This confirms my suspicion that it is KeyDrop and not KeyTake that is behaving badly.