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In [[nested array theory]], a nested array is an array of [[depth]] greater than one, that is, an array that contains at least one element which is not a [[simple scalar]]. It is roughly equivalent to a [[Box|boxed]] array in [[flat array theory]]; more precisely, non-[[mixed]] nested arrays correspond exactly to boxed arrays. Depending on language, an [[empty]] array may never be considered nested, or it may be considered nested if its [[prototype]] is nested. | In [[nested array theory]], a '''nested array''' is an array of [[depth]] greater than one, that is, an array that contains at least one element which is not a [[simple scalar]]. It is roughly equivalent to a [[Box|boxed]] array in [[flat array theory]]; more precisely, non-[[mixed]] nested arrays correspond exactly to boxed arrays. Depending on language, an [[empty]] array may never be considered nested, or it may be considered nested if its [[prototype]] is nested. | ||
[[Scalar functions]] descend into nested arrays one element at a time. Arrays can be nested at an arbitrary depth so this descent constitutes a traversal. Nested arrays form a [[tree]] structure with some additional information (the [[shape]]) at each node. | [[Scalar functions]] descend into nested arrays one element at a time. Arrays can be nested at an arbitrary depth so this descent constitutes a traversal. Nested arrays form a [[tree]] structure with some additional information (the [[shape]]) at each node. | ||
A nested array is a kind of [[pointer array]] and is almost always stored using pointers. | A nested array is a kind of [[pointer array]] and is almost always stored using pointers. | ||
The result of [[Enclose]] on an array other than a [[simple scalar]] is always a nested array. The [[Dyalog APL]] primitive [[Nest]] (<source lang=apl inline>⊆</source>), which encloses a [[simple]] argument, is named for this property: it applies the smallest transformation to turn the argument (unless it is a simple scalar) into a nested array. | |||
== See also == | |||
* [[NARS]], the first commercial nested APL implementation. | |||
{{APL features}}[[Category:Kinds of array]][[Category:Nested array model]] | |||