fixed in 10.0.2

Given data:

titanic = ExampleData[{"Dataset", "Titanic"}]

This Association Query works:

titanic[All, <| "newKey" -> "age"|>]

But numeric or Symbol Keys,

titanic[All, <| 1 -> "age"|>]
titanic[All, <| newKey -> "age"|>]

fail with error: Missing[KeyAbsent]. Known issue?

Numeric keys are especially conveninent for multiple, parametrized queries. Currently, that requires the workaround KeyMap[ToString] and later back ToExpression.


1 Answer 1


Ah, the <| field -> op |> constructor notation specifically requires string keys. I'll relax that -- should show up in 10.0.2.

  • $\begingroup$ For what it's worth: I noticed that if one relaxes that condition on Dataset`Query`PackagePrivate`comp then the correct results are generated. But then the result does not render properly in the front-end unless a similar relaxation is made to Dataset`FormattingDispatch`PackagePrivate`tocolboxes. I suspect that there could be similar knock-on consequences elsewhere. $\endgroup$
    – WReach
    Sep 8, 2014 at 21:18
  • 1
    $\begingroup$ @WReach it's not quite as bad as that: if we make the output type of ApplyThrough (the underlying operator form of <| |>) be an Assoc rather than Struct when keys aren't all strings, then everything downstream will Just Work. We lose a bit of type information -- but the only alternative, which is to allow Structs to contain keys of an arbitrary kind, is an invasive change that is unlikely to happen soon. $\endgroup$ Sep 9, 2014 at 16:23

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