This Q is related to this one, but now refer to the situation as irregularly distributed Keys in lists of Associations:

data4 = {<|"a" -> 1, "b" -> 2|>, <|"a" -> 3, "c" -> 4|>} // Dataset


data4[All, {"a" -> Framed, "b" -> Panel}] 

enter image description here

Of course this fails altogther:

data4[All, {"a" -> Framed, "b" -> Panel, "c" -> (Style[#, Red] &)}]

{Missing["Failed"], Missing["Failed"]}

Is there a better way than this clearly inefficient workaround using Lookup and subsequent filter out based on matching Missing? - To avoid having to add Missing handlers for each function:

data4[All, ({"a", "b", "c"} // AssociationMap[Lookup]) /* 
    Query[{"a" -> Framed, "b" -> Panel, "c" -> (Style[#, Red] &)}]][
  All, Select[FreeQ[#, Missing["KeyAbsent", "a" | "b" | "c"]] &]] // Normal

enter image description here

  • $\begingroup$ I wonder if its worth talking to Wolfram - it may be possible that the MissingBehaviour option of Query could be amended to deal with this, or that Query needs some additional intelligence to handle non uniform keys. $\endgroup$ May 15, 2015 at 8:05
  • $\begingroup$ Already submitted to WRI tech support. Hopefully b/w MissingBehavior, PartBehavior and FailureAction can rescue it. $\endgroup$ May 15, 2015 at 18:22
  • $\begingroup$ @GordonCoale, I think MissingBehavior should handle this option. Will contact support. $\endgroup$ Jul 13, 2016 at 19:54

1 Answer 1

data4 = {<|"a" -> 1, "b" -> 2|>, <|"a" -> 3, "c" -> 4|>} // Dataset

You could go with the answer from Query or MapAt ragged associations or ignoring Missing values

but let's create something more general since retyping keys is ugly:

mapping = {"a" -> Framed, "b" -> Panel, "c" -> (Style[#, Red] &)};

 Query[  FilterRules[mapping, #] ][#] &

enter image description here

  • $\begingroup$ That works nicely - interesting that FilterRules has been around pre v10. Heres's a slightly cleaned up version: filter[expr_][as_Association] := Query[FilterRules[expr, as]][as]; $\endgroup$ Jan 18, 2017 at 19:32
  • $\begingroup$ I belatedly noted some limitations of FilterRules in Q you linked above. $\endgroup$ Feb 8, 2017 at 19:09
  • $\begingroup$ @alancalvitti since no one is using FilterRules there maybe it is better to mention it here. $\endgroup$
    – Kuba
    Feb 8, 2017 at 19:31

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