3,038
edits
No edit summary |
(→Documentation: BQN link) |
||
(8 intermediate revisions by 2 users not shown) | |||
Line 1: | Line 1: | ||
{ | {| class=vertical-navbox style="float:right; font-size:500%; margin:0 1ex;" | ||
|<code>⊇</code> <code>@</code> | |||
|} | |||
'''From''' (<code>⊇</code> or <code>@</code> and also called '''Select''', or, [[humour]]ously, ''Sane Indexing'') is a [[primitive function]] that selects multiple [[major cell]]s of its right argument using an array of [[index|indices]] given by its left. The primitive often offers additional functionality for a [[nested]] left argument, which varies from one language to another. It appears in [[J]] (as <source lang=j inline>{</source>), [[Extended Dyalog APL]], [[dzaima/APL]], [[KAP]], and [[BQN]] (as <code>⊏</code>). | |||
== Common usage == | == Common usage == | ||
Line 8: | Line 11: | ||
fbdcea | fbdcea | ||
</source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}} | </source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}} | ||
Without Select, one would have to write <source lang=apl inline>Shuffle←⊢⌷⍨∘⊂?⍨∘≢</source>. | Without Select, one would have to write <source lang=apl inline>Shuffle←⊢⌷⍨∘⊂?⍨∘≢</source>. In this meaning, Select might be written as <source lang=apl inline>⌷⍨∘⊂⍨</source> or <source lang=apl inline>⌷⍤0 99</source> in [[Dyalog APL]] (where 99 exceeds the system's maximum array [[rank]]). | ||
In a case where the left argument is a permutation vector for the right argument, the functionality can rightfully be called ''Permute''. | In a case where the left argument is a permutation vector for the right argument, the functionality can rightfully be called ''Permute''. | ||
Line 18: | Line 21: | ||
bdace | bdace | ||
</source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}} | </source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}} | ||
== | |||
== Extensions == | |||
<source lang= | === Scatter-point === | ||
In [[A Dictionary of APL]], [[J]], and [[SAX]], a boxed left argument indicates that each [[element]] will be used independently to select a [[cell]] of the argument. The behavior on a single element is very similar to APL's [[Index (function)|Index]] function. <source lang=j inline>{</source> has a left [[Function rank|rank]] of 0, so that results are [[mix]]ed together and those with different shapes may be padded with [[fill]]s. | |||
<source lang=j> | |||
]a =. 4 4$(a.i.'A')}.a. | |||
ABCD | |||
EFGH | |||
IJKL | |||
MNOP | |||
0 3 2 { a | |||
ABCD | ABCD | ||
MNOP | MNOP | ||
IJKL | IJKL | ||
(0 0;3 3;2 3) { a | |||
APL | APL | ||
</source> | </source>{{Works in|[[J]]}} | ||
In APL this extension 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> | |||
== History == | |||
From (<code>{</code>) was introduced in 1986 by [[A Dictionary of APL]], with the same meaning now used in [[J]]. This description introduced the characteristic feature of selection of multiple cells simultaneously, as well as the pairing with monadic [[Catalogue]], scatter-point indexing, negative indices, and the ability to exclude rather than include indices using a third level of boxing. [[Roger Hui]] expressed his support for the new definition with a presentation at the next [[APL conference]]<ref>[[Roger Hui]]. [https://www.jsoftware.com/papers/from.htm Some Uses of <code>{</code> and <code>}</code>] at [[APL87]].</ref>, and it was included in J from the earliest drafts in 1990—a limited version had even appeared in [[Arthur Whitney]]'s one-page interpreter prototype. | |||
[[SHARP APL]] followed A Dictionary of APL and used <code>{</code>, but this was later deprecated, programmers being told to use <code>@</code> instead.<ref>Soliton Associates Limited. SHARP APL for UNIX Language Guide. [https://abrudz.github.io/SAX2/SAX61.pdf#G41.16516 Deprecated Primitives: Braces]. 2000.</ref> | |||
The name Select and glyph <code>⊇</code> were introduced by [[Extended Dyalog APL]], and subsequently adopted by [[dzaima/APL]] and [[KAP]]. | |||
[[BQN]] uses the name Select like Extended Dyalog APL but takes the direction of the glyph <code>⊏</code>, as well as negative indexing, from J. For a nested left argument it uses a new extension: instead of viewing nesting as elaboration of each element of the left argument, it instead treats it as providing a list of left arguments to select from multiple axes of the right argument. This extension provides the functionality of APL's [[Index (function)|Index]] not by requiring the left argument as a whole to be enclosed but by requiring that each of its elements be an array. | |||
== See also == | == See also == | ||
* [[Index (function)]] | * [[Index (function)]] | ||
* [[Bracket indexing]] | * [[Bracket indexing]] | ||
* [[Pick]] | * [[Pick]] | ||
== External links == | |||
=== Documentation === | |||
* J: [https://www.jsoftware.com/help/dictionary/d520.htm Dictionary], [https://code.jsoftware.com/wiki/Vocabulary/curlylf#dyadic Nuvoc] | |||
* [https://abrudz.github.io/SAX2/SAX61.pdf#M44.9.from SAX] | |||
* [https://mlochbaum.github.io/BQN/doc/select.html BQN] | |||
== References == | == References == | ||
<references/> | <references/> | ||
{{APL built-ins}}[[Category:Primitive functions]] | {{APL built-ins}}[[Category:Primitive functions]] |