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When extracting the "name" of an Entity one has CommonName. Good. Before I discovered this, I simply applied a rule like:

en = Entity["Language", "English"];
en /. Entity[a_, b_] :> b (* out: "English"*)

Maybe I´m missing something stupid, but why does the following not work?

Cases[en, Entity[a_, b_] :> b] (* out: {} *)
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  • $\begingroup$ Cases[{en}, Entity[a_, b_] :> b] works $\endgroup$
    – TimRias
    Jul 14, 2017 at 11:39
  • $\begingroup$ Related: reference.wolfram.com/language/ref/CanonicalName.html $\endgroup$
    – Greg Hurst
    Jul 17, 2017 at 4:43
  • $\begingroup$ That is not restricted to Entity that is the usual behavior of Cases, for example, for an undefined variable b, Cases[b,b] outputs {}. The fix-> Cases[en, Entity[a_, b_] :> b, All] $\endgroup$
    – userrandrand
    Nov 26, 2022 at 16:56

1 Answer 1

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You need to specify the levelspec as {0} using the third argument of Cases:

Cases[en, Entity[a_, b_] :> b, {0}]
(* or Cases[en, x_Entity:> Last[x], {0}] *)

{"English"}

Notes: from Cases >> Details and Options

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The last one explains why Cases[{en}, Entity[a_, b_] :> b] and, more generally, Cases[foo[en], Entity[a_, b_] :> b] gives {"English"}.

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  • $\begingroup$ Thank you! I knew it must be something stupid simple.... $\endgroup$
    – mgamer
    Jul 14, 2017 at 13:14
  • $\begingroup$ @mgamer, my pleasure. Thank you for the accept. It is easy to forget the three argument form of Cases:) $\endgroup$
    – kglr
    Jul 14, 2017 at 13:18

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