Array Lookup

From NARS2000
Jump to: navigation, search
Z←L⍸R returns a simple integer vector identical to (⊂⍤¯1 L)⍳⊂⍤(¯1+⍴⍴L) R.
L and R are arbitrary arrays.
Z is an array of rank 0⌈1+(⍴⍴R)-⍴⍴L and shape (1-⍴⍴L)↓⍴R.
For matrices, the result is equivalent to (⊂[2] L)⍳⊂[2] R (lookup the rows of one array in another) which encapsulates a common idiom in one symbol.
For higher rank arrays, the arguments are enclosed to become vectors of subarrays and then the usual lookup produces the final result.
This function is sensitive to both ⎕IO and ⎕CT.


For example, in origin-1

      ⎕←L←6 4⍴'DinaDickJohnJaneSue Mary'
Dina
Dick
John
Jane
Sue
Mary
      ⎕←R←3 4⍴'JaneBob Sue '
Jane
Bob
Sue
      L⍸R
4 7 5

This function was suggested by the language designers of Dyalog APL.