Take: Difference between revisions

Take (<code>↑</code>) is a [[primitive function]] which shortens or extends an array along one or more [[Axis|axes]]. The [[vector]] left argument indicates the lengths of result axes, with a sign to denote whether elements should be taken starting from the beginning or end of each axis. Take was introduced in [[APL\360]] with the requirement that the left argument length match the right argument rank, and was extended in [[SHARP APL]] to allow short left arguments. It is closely related to [[Drop]], which removes the parts of each axis that Take would include.

In the expression <code>X↑Y</code>, <code>X</code> may be any array, and <code>Y</code> is a [[Simple array|simple]] [[numeric]] [[vector]] whose length is less than or equal to the [[rank]] of <code>Y</code>. Many APLs require the length to be exactly equal; however, an extension by [[SHARP APL]] to allow a shorter left argument has been widely adopted by recent APLs. If <code>X</code> is a scalar, it may also be accepted and treated as a one-element vector in an instance of [[scalar rank extension]]. In some APLs, <code>Y</code> is also subject to [[scalar rank extension]]: if it is scalar then it will be extended so its rank is the length <code>≢X</code>.