Indices: Difference between revisions
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:''This page describes a primitive whose result is a list of indices. See [[Index]] for the page on indices themselves. See [[Index of]] for the index generator.'' | :''This page describes a primitive whose result is a list of indices. See [[Index]] for the page on indices themselves. See [[Index of]] for the index generator.'' | ||
{{Built-in|Indices|⍸}} or '''Where''', is a [[monadic]] [[primitive function]] which returns the [[Index|indices]] of all ones in a [[ | {{Built-in|Indices|⍸}} or '''Where''', is a [[monadic]] [[primitive function]] which returns the [[Index|indices]] of all ones in a [[Boolean]] array. More generally, Indices accepts an array of non-negative integers and copies each index the corresponding number of times. | ||
Indices was introduced in [[J]] as <source lang=j inline>I.</source> and is present in [[K]] as <source lang=k inline>&</source>. | Indices was introduced in [[J]] as <source lang=j inline>I.</source> and is present in [[K]] as <source lang=k inline>&</source>. | ||
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== Examples == | == Examples == | ||
In all implementations, Indices gives the indices of ones in a | In all implementations, Indices gives the indices of ones in a Boolean [[vector]]. | ||
<source lang=apl> | <source lang=apl> | ||
⍸ 0 0 1 0 0 0 1 0 | ⍸ 0 0 1 0 0 0 1 0 | ||
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{{Works in|[[Dyalog APL]], [[dzaima/APL]], [[NARS2000]], [[ngn/apl]]}} | {{Works in|[[Dyalog APL]], [[dzaima/APL]], [[NARS2000]], [[ngn/apl]]}} | ||
The argument is restricted to be an array of non-negative integers, or, in [[Dyalog APL]], | The argument is restricted to be an array of non-negative integers, or, in [[Dyalog APL]], Booleans. | ||
Because Indices returns indices (like [[Iota]]), it is subject to [[index origin]]. | Because Indices returns indices (like [[Iota]]), it is subject to [[index origin]]. | ||