Indexing: Difference between revisions
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<table border="0" cellpadding="5" cellspacing="0" summary=""> | <table border="0" cellpadding="5" cellspacing="0" summary=""> | ||
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<td valign="top"><apll>Z←R[L]</apll>, <apll>R[L]←A</apll>, <apll>R[L]<i>f</i>←A</apll>, <apll>L⌷R</apll>, and <apll>L⊃R</apll></td> | <td valign="top"><apll>Z←R[L]</apll>, <apll>R[L]←A</apll>, <apll>R[L]<i>f</i>←A</apll>, <apll>L⌷R</apll>, <apll>L⍉R</apll>, and <apll>L⊃R</apll></td> | ||
<td></td> | <td></td> | ||
<td></td> | <td></td> | ||
<td>are all extended to allow negative | <td>are all extended to allow negative values in <apll>L</apll>.</td> | ||
</tr> | </tr> | ||
</table> | </table> | ||
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<td><apll>L</apll> is a nested array of integer scalars and/or vectors, suitable for indexing <apll>R</apll>.</td> | <td>For all but transpose, <apll>L</apll> is a nested array of integer scalars and/or vectors, suitable for indexing <apll>R</apll>; for transpose, <apll>L</apll> is an integer scalar or vector of integers suitable for transposing <apll>R</apll>.</td> | ||
</tr> | </tr> | ||
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<td>That is, if the largest allowed | <td>That is, if the largest allowed value for <apll>L</apll> is <apll>N</apll>, then the previous allowable range of values was <apll>⎕IO</apll> to <apll>N</apll>, inclusive. Now, the allowable range of values is <apll>1 ¯1[1]-N</apll> to <apll>N</apll>, inclusive. For example, <apll>A</apll>, <apll>A[⍳⍴A]</apll>, <apll>A[⍳-⍴A]</apll>, and even <apll>A[⍳¯1 1[?(⍴⍴A)⍴2]×⍴A]</apll> are all identical for any array <apll>A</apll> in either origin.<br />Also, <apll>A</apll>, <apll>(⍳⍴⍴A)⍉A</apll>, and <apll>(⍳-⍴⍴A)⍉A</apll> are identical for any array <apll>A</apll> in either origin.</td> | ||
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Revision as of 13:53, 18 May 2009
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| L is a nested array of integer scalars and/or vectors, suitable for indexing R. | ||||
| R is an arbitrary array. | ||||
| A is an arbitrary array. | ||||
| Reach Indexing: If L⊃R is valid, it is equivalent to ⊃R[⊂L] | ||||
| Scatter Indexing: If L⌷R is valid, it is equivalent to R[⊃∘.,/L] | ||||
| Both Reach and Scatter indexing may appear together within a single instance of R[L], R[L]←A, and R[L]f←A |
For example, in origin-1
V←'123'(⊂4 5)
V[1 (2 ⍬ 1)]
123 4
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| For all but transpose, L is a nested array of integer scalars and/or vectors, suitable for indexing R; for transpose, L is an integer scalar or vector of integers suitable for transposing R. | ||||
| That is, if the largest allowed value for L is N, then the previous allowable range of values was ⎕IO to N, inclusive. Now, the allowable range of values is 1 ¯1[1]-N to N, inclusive. For example, A, A[⍳⍴A], A[⍳-⍴A], and even A[⍳¯1 1[?(⍴⍴A)⍴2]×⍴A] are all identical for any array A in either origin. Also, A, (⍳⍴⍴A)⍉A, and (⍳-⍴⍴A)⍉A are identical for any array A in either origin. |
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| R is an arbitrary array. | ||||
| A is an arbitrary array. |
For example, in origin-1
V←'123'(⊂4 5)
V[¯1 (0 ⍬ ¯1)]
123 4
