Array Lookup: Difference between revisions
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<td></td> | <td></td> | ||
<td>returns a simple integer vector identical to <apll>( | <td>returns a simple integer vector identical to <apll>(⊂⍤¯1 L)⍳⊂⍤(¯1+⍴⍴L) R</apll>.</td> | ||
</tr> | </tr> | ||
</table> | </table> | ||
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</tr> | </tr> | ||
<tr> | <tr> | ||
<td><apll>Z</apll> is an | <td><apll>Z</apll> is an array of rank <apll>0⌈1+(⍴⍴R)-⍴⍴L</apll> and shape <apll>(1-⍴⍴L)↓⍴R</apll>.</td> | ||
</tr> | </tr> | ||
<tr> | <tr> | ||
<td>For matrices, the result is equivalent to <apll>(⊂[2] L)⍳⊂[2] R</apll> which encapsulates a common idiom in one symbol.</td> | <td>For matrices, the result is equivalent to <apll>(⊂[2] L)⍳⊂[2] R</apll> (lookup the rows of one array in another) which encapsulates a common idiom in one symbol.</td> | ||
</tr> | </tr> | ||
<tr> | <tr> | ||
<td>For higher rank arrays, the arguments are enclosed to become vectors of subarrays and then the usual lookup produces the final result.</td> | <td>For higher rank arrays, the arguments are enclosed to become vectors of subarrays and then the usual lookup produces the final result.</td> | ||
</tr> | |||
<tr> | |||
<td>This function is sensitive to both <apll>⎕IO</apll> and <apll>⎕CT</apll>.</td> | |||
</tr> | </tr> | ||
</table> | </table> | ||
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<p>For example, in origin-1</p> | <p>For example, in origin-1</p> | ||
<apll> | <apll><pre> | ||
Dina | ⎕←L←6 4⍴'DinaDickJohnJaneSue Mary | ||
Dick | Dina | ||
John | Dick | ||
Jane | John | ||
Sue | Jane | ||
Mary | Sue | ||
Mary | |||
Jane | ⎕←R←3 4⍴'JaneBob Sue '<br /> | ||
Bob < | Jane | ||
Bob | |||
Sue | |||
L⍸R | |||
4 7 5</pre></apll> | |||
<p>This function was suggested by the language designers of Dyalog APL.</p> | |||
Latest revision as of 15:16, 15 April 2018
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| 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.
