4
$\begingroup$

The syntactic sugar for alternatives in replacement rules is clean:

{a|b|c-> 1, d->2}

Are there any analogous shorthands for keys in associations. I want to specify multiple equivalent keys in an association, like this:

<| Key[a|b|c]-> 1, Key[d]->2|>

The motivation is that sometimes the values in key-value pairs are large (and so you'd rather not flatten it out and add duplicate them for each key alias).

$ChordFormulas = <|"Major"|"Maj"->{0,4,7}, "m"|"Minor"|"Min" -> {0,3,7}, "9"|"79"->...|>

Related:

$\endgroup$
  • $\begingroup$ How do you want to use these associations? Are they constants or do you update (change) them frequently? If they are constants, Dispatch (or just a rule list) would work very well, I think. $\endgroup$ – Szabolcs Jan 19 '16 at 9:01
1
$\begingroup$

It seems you have already done it with Alternative.

c = <|"Major" | "Maj" -> {0, 4, 7}, "Minor" | "Min" -> {0, 3, 7}|>;

You would just need KeySelect and MatchQ.

KeySelect[MatchQ[#]@"Major" &]@c
(* <|"Major" | "Maj" -> {0, 4, 7}|> *)

or with ReplaceAll.

KeySelect["Maj" /. # -> True &]@c
(* <|"Major" | "Maj" -> {0, 4, 7}|> *)
$\endgroup$
  • $\begingroup$ In[211]:= <|"Major" | "Maj" -> {0, 4, 7}|>["Major"] Out[211]= Missing["KeyAbsent", "Major"] $\endgroup$ – M.R. Jan 19 '16 at 1:45
  • $\begingroup$ With this approach, everytime I do a query I'll need to use MatchQ which is slow. $\endgroup$ – M.R. Jan 19 '16 at 1:47
  • $\begingroup$ @M.R. Only way I can think of at the moment. It does allow you to use Alternatives and store the value once like you asked. $\endgroup$ – Edmund Jan 19 '16 at 1:48
  • $\begingroup$ @M.R. You can use ReplaceAll instead of MatchQ. "Maj" /. # -> True &. However, that will fall down if you ever use True as a key. $\endgroup$ – Edmund Jan 19 '16 at 1:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.