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{{Built-in|Select|⊇}} (jokingly referred to as ''Sane Indexing'') is a [[primitive function]] that allows selecting multiple [[major cell]]s using indices of the cells. It is equivalent to <source lang=apl inline>⌷⍨∘⊂⍨</source> and <source lang=apl inline>⌷⍤0 ∞</source>, only providing a neater notation for such a fundamental concept. It was introduced in [[Extended Dyalog APL]], and then adopted into [[dzaima/APL]] and [[KAP]].
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{{Built-in|Select|⊇}} ([[humour|jokingly]] referred to as ''Sane Indexing'') is a [[primitive function]] that allows selecting multiple [[major cell]]s using indices of the cells. It is equivalent to <source lang=apl inline>⌷⍨∘⊂⍨</source> and <source lang=apl inline>⌷⍤0 ∞</source>, only providing a neater notation for such a fundamental concept. It was introduced in [[Extended Dyalog APL]], and then adopted into [[dzaima/APL]] and [[KAP]].
  
 
== Common usage ==
 
== Common usage ==
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</source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}}
 
</source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}}
 
== Potential extension ==
 
== Potential extension ==
Select can be defined as <source lang=apl inline>⌷⍨∘⊃⍨⍤0 ∞</source> thus allowing both the above usage and "scatter point indexing":
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Select can be defined as <source lang=apl inline>⌷⍨∘⊃⍨⍤0 ∞</source> thus allowing both the above usage and "scatter point indexing":<ref>[[Richard Park]]. [https://dyalog.tv/Webinar/?v=AgYDvSF2FfU Selecting from Arrays]. [[Dyalog Webinar]]. 16 Apr 2020. (Presented in the form <source lang=apl inline>((⊃⊣)⌷⊢)⍤0 99</source>.)</ref>
 
<source lang=apl>
 
<source lang=apl>
 
       1 4 3 ⊇ 4 4⍴⎕A
 
       1 4 3 ⊇ 4 4⍴⎕A
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* [[Bracket indexing]]
 
* [[Bracket indexing]]
 
* [[Pick]]
 
* [[Pick]]
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== References ==
 +
<references/>
 
{{APL built-ins}}[[Category:Primitive functions]]
 
{{APL built-ins}}[[Category:Primitive functions]]

Revision as of 06:32, 11 May 2021

Select () (jokingly referred to as Sane Indexing) is a primitive function that allows selecting multiple major cells using indices of the cells. It is equivalent to ⍨∘ and 0 , only providing a neater notation for such a fundamental concept. It was introduced in Extended Dyalog APL, and then adopted into dzaima/APL and KAP.

Common usage

Select is commonly used to reorder the major cells of an array. For example, the following shuffles any array into random order:

Try it online!

      Shuffle?⍨∘
      Shuffle 'abcdef'
fbdcea

Without Select, one would have to write Shuffle⊢⌷⍨∘⊂?⍨∘.

In a case where the left argument is a permutation vector for the right argument, the functionality can rightfully be called Permute.

Select especially cleans up expressions for reordering. An ascending sort can be represented as and "sort by" can be written as ⍨∘:

Try it online!

      'abcde' ⍨∘ 3 1 4 1 5
bdace

Potential extension

Select can be defined as ⍨∘⍨⍤0 thus allowing both the above usage and "scatter point indexing":[1]

      1 4 3  4 4⎕A
ABCD
MNOP
IJKL
      (1 1)(4 4)(3 4)  4 4⎕A
APL

See also

References

  1. Richard Park. Selecting from Arrays. Dyalog Webinar. 16 Apr 2020. (Presented in the form ((⊃⊣)⌷⊢)0 99.)
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