Nest

From APL Wiki
(Redirected from Enclose if simple)
Jump to navigation Jump to search

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]
Primitive functions
Scalar
Monadic ConjugateNegateSignumReciprocalMagnitudeExponentialNatural LogarithmFloorCeilingFactorialNotPi TimesRollTypeImaginarySquare Root
Dyadic AddSubtractTimesDivideResiduePowerLogarithmMinimumMaximumBinomialComparison functionsBoolean functions (And, Or, Nand, Nor) ∙ GCDLCMCircularComplexRoot
Non-Scalar
Structural ShapeReshapeTallyDepthRavelEnlistTableCatenateReverseRotateTransposeRazeMixSplitEncloseNestCut (K)PairLinkPartitioned EnclosePartition
Selection FirstPickTakeDropUniqueIdentitySelectReplicateExpandSet functions (IntersectionUnionWithout) ∙ Bracket indexingIndex
Selector Index generatorGradeIndex OfInterval IndexIndicesDeal
Computational MatchNot MatchMembershipFindNub SieveEncodeDecodeMatrix InverseMatrix DivideFormatExecuteMaterialiseRange
Primitive operators Monadic EachCommuteConstantReplicateExpandReduceWindowed ReduceScanOuter ProductKeyI-BeamSpawnFunction axis
Dyadic BindCompositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner ProductPowerAtUnderRankDepthVariantStencilCut (J)
Quad names
Arrays Index originMigration levelAtomic vector
Functions Name classCase convertUnicode convert
Operators SearchReplace