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{{Built-ins|Nest|⊆|⊃}}, also called '''Conditional Enclose''' or '''Enclose If Simple''' (commonly abbreviated as '''eis''), is a [[monadic]] [[primitive function]] that applies [[Enclose]] to the given [[argument]], but only if it is [[simple]]. Nest first appeared as an extension to [[SHARP APL]]<ref>[https://www.jsoftware.com/papers/satn45.htm "Language Extensions of May 1983"]. SATN-45, 1983-05-02.</ref> using the [[glyph]] <source lang=apl inline>⊃</source>, and was added to [[Dyalog APL]] 16.0 using the glyph <source lang=apl inline>⊆</source>.
{{Built-ins|Nest|⊆|⊃}}, also called '''Conditional Enclose''' or '''Enclose If Simple''' (commonly abbreviated as '''eis'''), is a [[monadic]] [[primitive function]] that applies [[Enclose]] to the given [[argument]], but only if it is [[simple]]. Nest first appeared as an extension to [[SHARP APL]]<ref>[https://www.jsoftware.com/papers/satn45.htm "Language Extensions of May 1983"]. SATN-45, 1983-05-02.</ref> using the [[glyph]] <syntaxhighlight lang=apl inline>⊃</syntaxhighlight>, and was added to [[Dyalog APL]] 16.0 using the glyph <syntaxhighlight lang=apl inline>⊆</syntaxhighlight>.


== Examples ==
== Examples ==
Line 5: Line 5:
Nest is useful when a [[nested array]] is expected but the user may supply a simple array instead. For example, consider a function which expects one or more English words in uppercase and counts the words that include the letter E.
Nest is useful when a [[nested array]] is expected but the user may supply a simple array instead. For example, consider a function which expects one or more English words in uppercase and counts the words that include the letter E.


<source lang=apl>
<syntaxhighlight lang=apl>
       EWords←{+/'E'∊¨⍵}
       EWords←{+/'E'∊¨⍵}
</source>{{Works in|[[Dyalog APL]]}}
</syntaxhighlight>{{Works in|[[Dyalog APL]]}}


If the user gives multiple words in the usual notation, it works correctly:
If the user gives multiple words in the usual notation, it works correctly:


<source lang=apl>
<syntaxhighlight lang=apl>
       EWords 'I' 'ATE' 'DINNER' 'AND' 'WENT' 'TO' 'SLEEP'  ⍝ ATE, DINNER, WENT, SLEEP
       EWords 'I' 'ATE' 'DINNER' 'AND' 'WENT' 'TO' 'SLEEP'  ⍝ ATE, DINNER, WENT, SLEEP
4
4
</source>{{Works in|[[Dyalog APL]]}}
</syntaxhighlight>{{Works in|[[Dyalog APL]]}}


But if the user gives only one word, <source lang=apl inline>EWords</source> will count E's in each ''letter'' instead, giving the wrong answer:
But if the user gives only one word, <syntaxhighlight lang=apl inline>EWords</syntaxhighlight> will count E's in each ''letter'' instead, giving the wrong answer:


<source lang=apl>
<syntaxhighlight lang=apl>
       EWords 'SLEEP'
       EWords 'SLEEP'
2
2
</source>{{Works in|[[Dyalog APL]]}}
</syntaxhighlight>{{Works in|[[Dyalog APL]]}}


In this case, the programmer can apply Nest to the argument so that the array has a consistent structure.
In this case, the programmer can apply Nest to the argument so that the array has a consistent structure.


<source lang=apl>
<syntaxhighlight lang=apl>
       EWords2←{+/'E'∊¨⊆⍵}
       EWords2←{+/'E'∊¨⊆⍵}
       EWords2 'I' 'ATE' 'DINNER' 'AND' 'WENT' 'TO' 'SLEEP'
       EWords2 'I' 'ATE' 'DINNER' 'AND' 'WENT' 'TO' 'SLEEP'
Line 31: Line 31:
       EWords2 'SLEEP'
       EWords2 'SLEEP'
1
1
</source>{{Works in|[[Dyalog APL]]}}
</syntaxhighlight>{{Works in|[[Dyalog APL]]}}


== External links ==
== External links ==
Line 37: Line 37:
=== Documentation ===
=== Documentation ===


* [http://help.dyalog.com/latest/#Language/Primitive%20Functions/Nest.htm Dyalog]
* [https://help.dyalog.com/latest/#Language/Primitive%20Functions/Nest.htm Dyalog]


== References ==
== References ==

Latest revision as of 22:22, 10 September 2022

⊆ ⊃

Nest (⊆, ⊃), also called Conditional Enclose or Enclose If Simple (commonly abbreviated as eis), is a monadic primitive function that applies Enclose to the given argument, but only if it is simple. Nest first appeared as an extension to SHARP APL[1] using the glyph ⊃, and was added to Dyalog APL 16.0 using the glyph ⊆.

Examples

Nest is useful when a nested array is expected but the user may supply a simple array instead. For example, consider a function which expects one or more English words in uppercase and counts the words that include the letter E. 

      EWords←{+/'E'∊¨⍵}
Works in: Dyalog APL

If the user gives multiple words in the usual notation, it works correctly: 

      EWords 'I' 'ATE' 'DINNER' 'AND' 'WENT' 'TO' 'SLEEP'  ⍝ ATE, DINNER, WENT, SLEEP
4
Works in: Dyalog APL

But if the user gives only one word, EWords will count E's in each letter instead, giving the wrong answer: 

      EWords 'SLEEP'
2
Works in: Dyalog APL

In this case, the programmer can apply Nest to the argument so that the array has a consistent structure. 

      EWords2←{+/'E'∊¨⊆⍵}
      EWords2 'I' 'ATE' 'DINNER' 'AND' 'WENT' 'TO' 'SLEEP'
4
      EWords2 'SLEEP'
1
Works in: Dyalog APL

External links

Documentation

References

  1. ↑ "Language Extensions of May 1983". SATN-45, 1983-05-02.


APL built-ins [edit]
Primitives (Timeline) Functions
Scalar
Monadic Conjugate ∙ Negate ∙ Signum ∙ Reciprocal ∙ Magnitude ∙ Exponential ∙ Natural Logarithm ∙ Floor ∙ Ceiling ∙ Factorial ∙ Not ∙ Pi Times ∙ Roll ∙ Type ∙ Imaginary ∙ Square Root ∙ Round
Dyadic Add ∙ Subtract ∙ Times ∙ Divide ∙ Residue ∙ Power ∙ Logarithm ∙ Minimum ∙ Maximum ∙ Binomial ∙ Comparison functions ∙ Boolean functions (And, Or, Nand, Nor) ∙ GCD ∙ LCM ∙ Circular ∙ Complex ∙ Root
Non-Scalar
Structural Shape ∙ Reshape ∙ Tally ∙ Depth ∙ Ravel ∙ Enlist ∙ Table ∙ Catenate ∙ Reverse ∙ Rotate ∙ Transpose ∙ Raze ∙ Mix ∙ Split ∙ Enclose ∙ Nest ∙ Cut (K) ∙ Pair ∙ Link ∙ Partitioned Enclose ∙ Partition
Selection First ∙ Pick ∙ Take ∙ Drop ∙ Unique ∙ Identity ∙ Stop ∙ Select ∙ Replicate ∙ Expand ∙ Set functions (Intersection ∙ Union ∙ Without) ∙ Bracket indexing ∙ Index ∙ Cartesian Product ∙ Sort
Selector Index generator ∙ Grade ∙ Index Of ∙ Interval Index ∙ Indices ∙ Deal ∙ Prefix and suffix vectors
Computational Match ∙ Not Match ∙ Membership ∙ Find ∙ Nub Sieve ∙ Encode ∙ Decode ∙ Matrix Inverse ∙ Matrix Divide ∙ Format ∙ Execute ∙ Materialise ∙ Range
Operators Monadic Each ∙ Commute ∙ Constant ∙ Replicate ∙ Expand ∙ Reduce ∙ Windowed Reduce ∙ Scan ∙ Outer Product ∙ Key ∙ I-Beam ∙ Spawn ∙ Function axis ∙ Identity (Null, Ident)
Dyadic Bind ∙ Compositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner Product ∙ Determinant ∙ Power ∙ At ∙ Under ∙ Rank ∙ Depth ∙ Variant ∙ Stencil ∙ Cut ∙ Direct definition (operator) ∙ Identity (Lev, Dex)
Quad names Index origin ∙ Comparison tolerance ∙ Migration level ∙ Atomic vector
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