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Tally: Difference between revisions
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Tally can compute the length of a [[numeric]] [[vector]] or [[string]]. | Tally can compute the length of a [[numeric]] [[vector]] or [[string]]. | ||
< | <syntaxhighlight lang=apl> | ||
≢⍳12 | ≢⍳12 | ||
12 | 12 | ||
| Line 11: | Line 11: | ||
</syntaxhighlight> | </syntaxhighlight> | ||
It gives the length of the first [[axis]] in a higher-rank array. Tally applied to an array's [[shape]] gives its [[rank]]. | It gives the length of the first [[axis]] in a higher-rank array. Tally applied to an array's [[shape]] gives its [[rank]]. | ||
< | <syntaxhighlight lang=apl> | ||
≢5 4 3 2⍴1 'b' 3 'd' | ≢5 4 3 2⍴1 'b' 3 'd' | ||
5 | 5 | ||
| Line 18: | Line 18: | ||
</syntaxhighlight> | </syntaxhighlight> | ||
The Tally of a [[scalar]] is always 1. | The Tally of a [[scalar]] is always 1. | ||
< | <syntaxhighlight lang=apl> | ||
≢3.14 | ≢3.14 | ||
1 | 1 | ||
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Tally returns the length of the first [[axis]] of its argument if it has any axes (that is, if it is not a scalar), and 1 otherwise. This can be modelled easily with [[Shape]] and [[First]]: | Tally returns the length of the first [[axis]] of its argument if it has any axes (that is, if it is not a scalar), and 1 otherwise. This can be modelled easily with [[Shape]] and [[First]]: | ||
< | <syntaxhighlight lang=apl> | ||
Tally ← {⊃(⍴⍵),1} | Tally ← {⊃(⍴⍵),1} | ||
</syntaxhighlight> | </syntaxhighlight> | ||
An alternative implementation is to count the major cells by turning each into a scalar 1 with the [[Rank operator]], then adding them up: | An alternative implementation is to count the major cells by turning each into a scalar 1 with the [[Rank operator]], then adding them up: | ||
< | <syntaxhighlight lang=apl> | ||
Tally ← +⌿ {1}⍤¯1 | Tally ← +⌿ {1}⍤¯1 | ||
</syntaxhighlight> | </syntaxhighlight> | ||
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== History == | == History == | ||
Tally was introduced in [[A]] with the name "count" and symbol < | Tally was introduced in [[A]] with the name "count" and symbol <syntaxhighlight lang=j inline>#</syntaxhighlight>. The same notation was carried forward to [[A+]], as well as [[J]] following [[Arthur Whitney]]'s suggestion. The primitive was present in [[NARS2000]] by 2010, with the name "Tally" and symbol <syntaxhighlight lang=apl inline>></syntaxhighlight><ref>NARS2000 Wiki. [http://wiki.nars2000.org/index.php?title=Tally&oldid=573 Tally]. Old revision: 2010-08-29.</ref>. The symbol <syntaxhighlight lang=apl inline>≢</syntaxhighlight> for Tally was introduced in [[Dyalog APL 14.0]], and quickly adopted by NARS2000. It was later added to [[GNU APL]] and has been included in many recent APLs based on Dyalog, such as [[ngn/apl]], [[dzaima/APL]], and [[APL\iv]]. | ||
Before the addition of Tally (and [[Zilde]]), there were numerous ways to get the length of a vector as a scalar:<ref>[[Roger Hui]] and [[Morten Kromberg]]. [https://dl.acm.org/doi/abs/10.1145/3386319 ''APL since 1978'']. §2.1 Tally. ACM [[HOPL]] IV. 2020-06.</ref> | Before the addition of Tally (and [[Zilde]]), there were numerous ways to get the length of a vector as a scalar:<ref>[[Roger Hui]] and [[Morten Kromberg]]. [https://dl.acm.org/doi/abs/10.1145/3386319 ''APL since 1978'']. §2.1 Tally. ACM [[HOPL]] IV. 2020-06.</ref> | ||
< | <syntaxhighlight lang=apl> | ||
''⍴⍴v | ''⍴⍴v | ||
(⍴0)⍴⍴v | (⍴0)⍴⍴v | ||