From: Difference between revisions

{{Built-in|From|{}} or '''Select''' (<code>⊇</code>, or <code>⊏</code> in [[BQN]]) (sometimes [[humour]]ously called ''Sane Indexing'') is a [[primitive function]] that selects multiple [[major cell]]s of its right argument using an array of [[index|indices]] given by its left. The primitive often offers additional functionality for a [[nested]] left argument, which varies from one language to another. It appears in [[J]], [[Extended Dyalog APL]], [[dzaima/APL]], [[KAP]], and [[BQN]].

From (<code>{</code>) was introduced in 1986 by [[A Dictionary of APL]], with the same meaning now used in [[J]]. This description introduced the characteristic feature of selection of multiple cells simultaneously, as well as the pairing with monadic [[Catalogue]], scatter-point indexing, negative indices, and the ability to exclude rather than include indices using a third level of boxing. [[Roger Hui]] expressed his support for the new definition with a presentation at the next [[APL conference]]<ref>[[Roger Hui]]. [https://www.jsoftware.com/papers/from.htm Some Uses of { and }] at [[APL87]].</ref>, and it was included in J from the earliest drafts in 1990—a limited version had even appeared in [[Arthur Whitney]]'s one-page interpreter prototype.