Difference between revisions of "Array Lookup"

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<p>For example, in origin-1</p>
 
<p>For example, in origin-1</p>
  
<apll>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;⎕←L←6 4⍴'DinaDickJohnJaneSue Mary'<br />
+
<apll><pre>
Dina<br />
+
      ⎕←L←6 4⍴'DinaDickJohnJaneSue Mary
Dick<br />
+
Dina
John<br />
+
Dick
Jane<br />
+
John
Sue <br />
+
Jane
Mary<br />
+
Sue  
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;⎕←R←3 4⍴'JaneBob Sue '<br />
+
Mary
Jane<br />
+
      ⎕←R←3 4⍴'JaneBob Sue '<br />
Bob <br />
+
Jane
Sue <br />
+
Bob  
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;L⍸R<br />
+
Sue  
4 7 5</apll>
+
      L⍸R
 +
4 7 5</pre></apll>
  
 
<p>This function was suggested by the language designers of Dyalog APL.</p>
 
<p>This function was suggested by the language designers of Dyalog APL.</p>

Latest revision as of 20:16, 15 April 2018

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.