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19:14
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A: How to organically merge nested associations?

alancalvittiTry this, we're using it on a daily basis Nest[Merge,f,n] To your starting data, slightly modified (strings vs symbols): peopleFacts = <|"alice" -> <|"age" -> 29, "shoeSize" -> 7|>, "bob" -> <|"age" -> 27, "sex" -> "male"|>|>; And new facts: newFacts = <| "steve" -> <|"hairColor" -> ...

Kuba
Kuba
what is f and n here?
alancalvitti
alancalvitti
Nest[Merge, expr, n] gives an expression with Merge applied n times to f.
Kuba
Kuba
You can assume I am aware of documentation :) But where do I put the initial association and the update association?
alancalvitti
alancalvitti
Use it as an operator, no different than using Merge by itself or iterated Merge[Merge[...]]
Kuba
Kuba
Could you take the example from my answer and demonstrate?
alancalvitti
alancalvitti
19:14
@Kuba, see edits
Kuba
Kuba
@alancalvitti thanks but I'm still missing something, try: 
{<|bob -> <|age -> 27, sex -> male,  hobby -> <|mma -> 1, mo -> 1|>|>|>, <|bob -> <|age -> 22,  hobby -> <|mo -> 2|>|>|>} // Nest[Merge, Last, 2]
returns 
<|bob -> <|age -> 22, sex -> male, hobby -> <|mo -> 2|>|>|>
{<|bob -> <|age -> 27, sex -> male,
     hobby -> <|mma -> 1, mo -> 1|>|>|>, <|bob -> <|age -> 22,
     hobby -> <|mo -> 2|>|>|>} // MergeNested
returns 
<|bob -> <|age -> 22, sex -> male, hobby -> <|mma -> 1, mo -> 2|>|>|>
I don't think mma->1 should have been dropped.
so it won't work if the nested association is 'ragged'.
alancalvitti
alancalvitti
20:06
I pointed out ragged Associations are an issue but didn't consider that these come up naturally in the OP's setting.
Try this though: merge[f_][as : {_Association ..}] := Merge[f][as];
merge[f_][nas : {Except[_Association] ..}] := f[nas];
Probably a recursive approach would be more robust, using a similar check on the Heads of objects being merged
Kuba
Kuba
20:42
@alancalvitti right, clearly I wasn't paying attention. Don't know if it matters performance wise but yes, if on often works with the same structure it can be useful. Thanks for taking your time to add explanation.
alancalvitti
alancalvitti
20:55
So does the approach above work in all cases considered by OP? If so I'll add it to my answer.

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