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A '''singleton''' is an array with [[bound]] 1. Equivalently, its [[shape]] consists entirely of 1s. It may have any [[rank]]. | A '''singleton''' is an [[Array model|array]] with [[bound]] 1. Equivalently, its [[shape]] consists entirely of 1s. It may have any [[rank]]. For example, all the following are singletons: | ||
* The [[scalar]] <source lang=apl inline>42</source> | |||
* The [[vector]] <source lang=apl inline>,42</source> | |||
* The [[matrix]] <source lang=apl inline>⍪42</source> | |||
* The three-[[dimension]]al array <source lang=apl inline>1 1 1⍴42</source> | |||
* The [[nested]] scalar <source lang=apl inline>⊂4 2</source> | |||
Whether an array <source lang=apl inline>X</source> is a singleton can be determined with <source lang=apl inline>1=×/⍴X</source> or, less efficiently, with <source lang=apl inline>1=≢,X</source>. | |||
Every scalar <source lang=apl inline>X</source> is a singleton, because <source lang=apl inline>1=×/⍴X</source>, or alternatively <source lang=apl inline>1=≢,X</source>. | |||
Singletons may be subject to [[singleton extension]]. | Singletons may be subject to [[singleton extension]]. | ||
{{APL features}}[[Category:Kinds of array]] | |||