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{{Built-ins|Scan|<nowiki>\</nowiki>|⍀}} is a [[primitive operator|primitive]] [[monadic operator]] which takes a [[dyadic function]] [[operand]] and produces a [[monadic function]] which is equivalent to the [[reduce|reductions]] of the | {{Built-ins|Scan|<nowiki>\</nowiki>|⍀}} is a [[primitive operator|primitive]] [[monadic operator]] which takes a [[dyadic function]] [[operand]] and produces a [[monadic function]] which is equivalent to the [[reduce|reductions]] of the [[prefix]]es of the arguments. This operation is known as also known as cumulative reduction. | ||
== Explanation == | == Explanation == | ||
| Line 5: | Line 5: | ||
== Examples == | == Examples == | ||
< | <syntaxhighlight lang=apl> | ||
+\⍳5 ⍝ plus-scan over range of integers from 1 to 5 | +\⍳5 ⍝ plus-scan over range of integers from 1 to 5 | ||
1 3 6 10 15 | 1 3 6 10 15 | ||
</ | </syntaxhighlight> | ||
== Applications == | == Applications == | ||
Removing disconnected trailing 1s from a [[boolean]] mask: | Removing disconnected trailing 1s from a [[boolean]] mask: | ||
< | <syntaxhighlight lang=apl> | ||
mask←1 1 1 1 0 1 1 0 0 1 | mask←1 1 1 1 0 1 1 0 0 1 | ||
mask | mask | ||
| Line 18: | Line 18: | ||
∧\mask ⍝ and-scan mask | ∧\mask ⍝ and-scan mask | ||
1 1 1 1 0 0 0 0 0 0 | 1 1 1 1 0 0 0 0 0 0 | ||
</ | </syntaxhighlight> | ||
== External links == | == External links == | ||
=== Lessons === | === Lessons === | ||
| Line 25: | Line 25: | ||
* [https://help.dyalog.com/latest/#Language/Primitive%20Operators/Scan.htm Dyalog] | * [https://help.dyalog.com/latest/#Language/Primitive%20Operators/Scan.htm Dyalog] | ||
* [https://microapl.com/apl_help/ch_020_020_820.htm APL] | * [https://microapl.com/apl_help/ch_020_020_820.htm APL] | ||
* [https://mlochbaum.github.io/BQN/doc/scan.html BQN] | |||
{{APL built-ins}}[[Category:Primitive operators]] | {{APL built-ins}}[[Category:Primitive operators]] | ||
Latest revision as of 21:02, 10 September 2022
\ ⍀
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Scan (\, ⍀) is a primitive monadic operator which takes a dyadic function operand and produces a monadic function which is equivalent to the reductions of the prefixes of the arguments. This operation is known as also known as cumulative reduction.
Explanation
Scan is similar to Reduce, however all the intermediate results will be retained. That being said, unlike Reduce, Scan does not reduce the rank of its argument, i.e. performing a scan over an N-dimensional array will produce an N-dimensional array.
Examples
+\⍳5 ⍝ plus-scan over range of integers from 1 to 5 1 3 6 10 15
Applications
Removing disconnected trailing 1s from a boolean mask:
mask←1 1 1 1 0 1 1 0 0 1
mask
1 1 1 1 0 1 1 0 0 1
∧\mask ⍝ and-scan mask
1 1 1 1 0 0 0 0 0 0
External links
Lessons
Documentation