Drop: Difference between revisions

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Drop (view source)

Revision as of 21:23, 10 September 2022

144 bytes added ,  21:23, 10 September 2022
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Text replacement - "</source>" to "</syntaxhighlight>"
m (Text replacement - "<source" to "<syntaxhighlight")
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       ¯3 ↓ 5 4 3 2 1
       ¯3 ↓ 5 4 3 2 1
5 4
5 4
</source>
</syntaxhighlight>


Removing more elements than the length of the axis gives an [[empty]] result:
Removing more elements than the length of the axis gives an [[empty]] result:
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       ¯8 ↓ 5 4 3 2 1
       ¯8 ↓ 5 4 3 2 1


</source>
</syntaxhighlight>
{{Works in|[[Dyalog APL]], [[ngn/apl]]}}
{{Works in|[[Dyalog APL]], [[ngn/apl]]}}


Line 26: Line 26:
│4 4│4 5│
│4 4│4 5│
└───┴───┘
└───┴───┘
</source>
</syntaxhighlight>


== Description ==
== Description ==
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The arguments to Drop must be valid arguments to [[Take]], and elements of the left argument are matched to [[axes]] of the right in the same way. Like Take, the left argument is subject to [[scalar rank extension]], and in some APLs the right is as well.
The arguments to Drop must be valid arguments to [[Take]], and elements of the left argument are matched to [[axes]] of the right in the same way. Like Take, the left argument is subject to [[scalar rank extension]], and in some APLs the right is as well.


Each axis with a matching left argument element <syntaxhighlight lang=apl inline>d</source> is modified to remove <syntaxhighlight lang=apl inline>|d</source> indices, or all of them if <syntaxhighlight lang=apl inline>|d</source> is larger than the length of the axis. Indices are removed starting from the beginning if <syntaxhighlight lang=apl inline>d</source> is positive and starting from the end if it is negative (if <syntaxhighlight lang=apl inline>d</source> is 0, then no indices are removed). Equivalently, for an axis of length <syntaxhighlight lang=apl inline>l</source>, <syntaxhighlight lang=apl inline>l-l⌊|d</source> axes are retained—not dropped—from the axis starting from the opposite side: the end if <syntaxhighlight lang=apl inline>d</source> is positive and the beginning otherwise. If <syntaxhighlight lang=apl inline>|d</source> is greater than or equal to <syntaxhighlight lang=apl inline>l</source> for any axis, then the result is [[empty array|empty]] and shares a [[prototype]] with the argument.
Each axis with a matching left argument element <syntaxhighlight lang=apl inline>d</syntaxhighlight> is modified to remove <syntaxhighlight lang=apl inline>|d</syntaxhighlight> indices, or all of them if <syntaxhighlight lang=apl inline>|d</syntaxhighlight> is larger than the length of the axis. Indices are removed starting from the beginning if <syntaxhighlight lang=apl inline>d</syntaxhighlight> is positive and starting from the end if it is negative (if <syntaxhighlight lang=apl inline>d</syntaxhighlight> is 0, then no indices are removed). Equivalently, for an axis of length <syntaxhighlight lang=apl inline>l</syntaxhighlight>, <syntaxhighlight lang=apl inline>l-l⌊|d</syntaxhighlight> axes are retained—not dropped—from the axis starting from the opposite side: the end if <syntaxhighlight lang=apl inline>d</syntaxhighlight> is positive and the beginning otherwise. If <syntaxhighlight lang=apl inline>|d</syntaxhighlight> is greater than or equal to <syntaxhighlight lang=apl inline>l</syntaxhighlight> for any axis, then the result is [[empty array|empty]] and shares a [[prototype]] with the argument.


=== APL Model ===
=== APL Model ===
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     ((sׯ1*⍺>0) + (-s)⌈s⌊⍺) ↑ ⍵
     ((sׯ1*⍺>0) + (-s)⌈s⌊⍺) ↑ ⍵
}
}
</source>
</syntaxhighlight>
The code works by modifying the left argument using the right argument's shape. First, the shape is used to restrict the left argument's range (<syntaxhighlight lang=apl inline>(-s)⌈s⌊⍺</source>) so that the maximum number of indices dropped is the length of the axis. Then, the shape is added or subtracted so that the left argument's sign is flipped.
The code works by modifying the left argument using the right argument's shape. First, the shape is used to restrict the left argument's range (<syntaxhighlight lang=apl inline>(-s)⌈s⌊⍺</syntaxhighlight>) so that the maximum number of indices dropped is the length of the axis. Then, the shape is added or subtracted so that the left argument's sign is flipped.


This implementation inherits all argument extensions from Take. The two middle lines are used to support right argument scalar rank extension and the [[SHARP APL]] short left argument extension. If Take does not have these extensions then they have no effect and can be removed.
This implementation inherits all argument extensions from Take. The two middle lines are used to support right argument scalar rank extension and the [[SHARP APL]] short left argument extension. If Take does not have these extensions then they have no effect and can be removed.
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* [http://microapl.com/apl_help/ch_020_020_570.htm APLX]
* [http://microapl.com/apl_help/ch_020_020_570.htm APLX]


* [https://www.jsoftware.com/help/dictionary/d531.htm J Dictionary], [https://code.jsoftware.com/wiki/Vocabulary/curlyrtdot#dyadic J NuVoc] (as <syntaxhighlight lang=apl inline>}.</source>)
* [https://www.jsoftware.com/help/dictionary/d531.htm J Dictionary], [https://code.jsoftware.com/wiki/Vocabulary/curlyrtdot#dyadic J NuVoc] (as <syntaxhighlight lang=apl inline>}.</syntaxhighlight>)


* [https://mlochbaum.github.io/BQN/doc/take.html BQN]
* [https://mlochbaum.github.io/BQN/doc/take.html BQN]
{{APL built-ins}}[[Category:Primitive functions]]
{{APL built-ins}}[[Category:Primitive functions]]
Retrieved from ‘https://aplwiki.com/wiki/Special:MobileDiff/9276’

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