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Simpler fix for length-1 case
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(Simpler fix for length-1 case) |
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</syntaxhighlight> | </syntaxhighlight> | ||
{{Works in|[[Dyalog APL]]}} | {{Works in|[[Dyalog APL]]}} | ||
The accumulation above resembles a [[reduction]]—in fact, it is a reverse [[insertion]]. The following implementation written with Reduce works for [[simple]] vectors in [[Nested array model|nested]] APLs because reduction is equivalent to insertion followed by [[Enclose]] on such vectors: | The accumulation above resembles a [[reduction]]—in fact, it is a reverse [[insertion]] (reversing is necessary when using tolerant comparison as cells need to be added in order). The following implementation written with Reduce works for non-empty [[simple]] vectors in [[Nested array model|nested]] APLs because reduction is equivalent to insertion followed by [[Enclose]] on such vectors: | ||
<syntaxhighlight lang=apl> | <syntaxhighlight lang=apl> | ||
VecUnique ← {⊃∪⍨/⌽⍵} | VecUnique ← {⊃∪⍨/⌽⍵} | ||
</syntaxhighlight> | </syntaxhighlight> | ||
{{Works in|[[Dyalog APL]],[[ngn/apl]]}} | {{Works in|[[Dyalog APL]],[[ngn/apl]]}} | ||
It | It is extended to empty, nested, and arbitrary rank inputs as follows: | ||
<syntaxhighlight lang=apl> | <syntaxhighlight lang=apl> | ||
m ← {0=≢⍵:⍵ ⋄ ↑,⊃∪⍨/⌽⊂¨⊂⍤¯1⊢⍵} | |||
</syntaxhighlight> | </syntaxhighlight> | ||
{{Works in|[[Dyalog APL]]}} | {{Works in|[[Dyalog APL]]}} | ||
The guard checks for length zero because <syntaxhighlight lang=apl inline>∪⍨</syntaxhighlight> lacks an [[identity element]]. The [[Replicate]] call <syntaxhighlight lang=apl inline>1/⍵</syntaxhighlight> converts a scalar to a vector, and the encloses ensure that the array added by Union is always a scalar. | |||
While the model <syntaxhighlight lang=apl inline>{((⍳≢⍵)=(⍵⍳⍵))⌿⍵}</syntaxhighlight>, based on [[Nub Sieve]], is often described as an implementation of Unique, it does not correctly handle [[tolerant comparison]].<ref>Hui, Roger. [https://dyalog.tv/Dyalog17/?v=fPWky9IOG40 Tolerant Unique]. [[Dyalog '17]].</ref> A correct implementation of Nub Sieve could be used to implement Unique, but writing such an implementation is no easier than implementing Unique directly. | If modelling the primitive via Union is not desirable due to how similar these two primitives are, it is possible to replace this particular usage of union (not generally, as it relies on the right argument being scalar) as follows: | ||
<syntaxhighlight lang=apl> | |||
m ← {0=≢⍵:⍵ ⋄ ↑,⊃{⍺,(∧/⍺≢¨⍵)/⍵}⍨/⌽⊂¨⊂⍤¯1⊢⍵} | |||
</syntaxhighlight> | |||
{{Works in|[[Dyalog APL]]}} | |||
While the model <syntaxhighlight lang=apl inline>{((⍳≢⍵)=(⍵⍳⍵))⌿⍵}</syntaxhighlight> for vector arguments, based on [[Nub Sieve]], is often described as an implementation of Unique, it does not correctly handle [[tolerant comparison]].<ref>Hui, Roger. [https://dyalog.tv/Dyalog17/?v=fPWky9IOG40 Tolerant Unique]. [[Dyalog '17]].</ref> A correct implementation of Nub Sieve could be used to implement Unique, but writing such an implementation is no easier than implementing Unique directly. | |||
== Properties == | == Properties == | ||