Problem Using Evaluated Replace with Associations

Question

If I define some function like:

toISOdate[data_List]:=DateString[data,{"Year","-","Month","-","Day"}]

and try to applicate it in an Association

ass = <|"date" -> {{2014, 1, 1}, {2014, 1, 2}}|>

as:

Replace[ass, a:{_, _, _} :> toISOdate[a], ∞]

I get, the non calculated form:

<|"date" -> {toISOdate[{2014, 1, 1}], toISOdate[{2014, 1, 2}]}|>

instead of

<|"date" -> {"2014-01-01", "2014-01-02"}|>

If I use Normal into ass as:

Replace[Normal@ass, (a : {_, _, _}) :> toISOdate[a], ∞]

I get the correct calculation, but lose the association form.

Is this a bug? How can I get it evaluated with Association?

Using Mathematica V10.1 on Mac

PS: I can't loose the association structure, the real case is more complex.

Update:

ass /. a : {_, _, _} :> toISOdate[a]

Works as expected.

If you assign the result of the Replace function to a variable, and recall it, it's correct (v 10.2 Mac OS X). a = Replace[....]; a["date"] — kale, Jul 29 '15 at 23:31
@Mr.Wizard I'm on Mac. I edited the question to add this information tks. — Murta, Jul 29 '15 at 23:32

score 5 · Accepted Answer · edited Apr 13 '17 at 12:56

5

Taliesin Beynon stated in reply to Held keys in associations:

Keys have to remain unevaluated for associations to have any efficiency advantages over ordinary lists of rules. There's no way around that.

Apparently this is simply another manifestation of Replacement inside held expression and the same solution applies:

Replace[ass, a : {_, _, _} :> RuleCondition @ toISOdate[a], -2]

<|"date" -> {"2014-01-01", "2014-01-02"}|>

The question then becomes why does ReplaceAll cause evaluation? I think it should not, and I think that is a bug just as it is for Map and AssociationMap.

edited Apr 13 '17 at 12:56

Community

1

answered Jul 29 '15 at 23:40

Mr.Wizard

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RuleCondition is undocumented no? +1 – Murta Jul 30 '15 at 00:28
@Murta Yes indeed, but very convenient. WReach introduced it to public use (at least within Stack Exchange) here, I believe. – Mr.Wizard Jul 30 '15 at 01:47
Very interesting to know. – Murta Jul 30 '15 at 01:51
@Murta I just realized a major problem with this answer: Taliesin said *Keys* have to remain unevaluated, not values. Is this intended therefore? I don't know. I'll ask him. – Mr.Wizard Jul 30 '15 at 17:30
so we should tag this post like a bug? – Murta Jul 30 '15 at 17:58
@Murta No, wait for clarification from Tali. I think I still have the right interpretation, that he did not mean only keys but wrote keys because that's what my prior question was about, but I'll correct this answer if I am wrong. – Mr.Wizard Jul 30 '15 at 18:08
1

@Mr.Wizard This feels like a bug to me... consider reporting it to Tech Support and I'll see what various other people in the company think. – Taliesin Beynon Jul 31 '15 at 04:32
@Tali Thanks! But which part, Replace, or ReplaceAll? – Mr.Wizard Jul 31 '15 at 04:35
@Mr.Wizard Replace – Taliesin Beynon Aug 07 '15 at 22:25
Is there any new information on whether this is really a bug & will be fixed? I'm still having the same issue in V11.0.1: <|"key" -> a + b|> /. {a -> 1, b -> 2} gives <|"key" -> 1 + 2|> and not <|"key" -> 3|>. – mjayvizzle Feb 08 '17 at 09:30
@TaliesinBeynon do you care to reply to the comment immediately above? – Mr.Wizard Feb 08 '17 at 09:37
2

@Mr.Wizard I don't like this behavior and I've advocated against it within the company. Did you report it as a bug to Tech Support? – Taliesin Beynon Mar 19 '17 at 11:59

Problem Using Evaluated Replace with Associations

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