Pair

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Revision as of 16:40, 6 March 2024 by Marshall (talk | contribs) (→‎History: Link in SHARP and J, Enlist in K, Pair in I)
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⍮

Pair (⍮) or Juxtapose is a primitive ambivalent function that constructs a vector of its arguments, present in Extended Dyalog APL, dzaima/APL, and BQN (as ⋈). The monadic case is referred to as Half Pair in Extended Dyalog APL, and is similar to Enclose except that it gives a result of rank 1 rather than 0. This case is called Enlist in BQN, as well as K, where it is the monadic case of , (K has no dyadic Pair primitive). Dyadic Pair is similar to the Link primitive in SHARP APL and J, but Link has an asymmetric definition that adds its left argument to a vector right argument rather than creating a new vector.

Pair can be implemented as the dfn {⍺←,⊂ ⋄ ⍺ ⍵}, or the catenation of the enclosed arguments, written ,⍥⊂ using Over.[1] Pair aids in constructing nested arrays in tacit programming, where stranding by juxtaposition is not available.

Common usage

Its plain usage is in pairing up two parallel values:

Try it online! 

      6 7 8(+⍮-)3
┌───────┬─────┐
│9 10 11│3 4 5│
└───────┴─────┘
Works in: dzaima/APL, Extended Dyalog APL

It can also be combined with Mix to increase rank rather than depth:

Try it online! 

      6 7 8(+↑⍤⍮-)3
9 10 11
3  4  5
Works in: dzaima/APL, Extended Dyalog APL

History

Link precedes Pair significantly, as it was defined in SHARP APL in 1983,[2] and included in the initial version of J in 1990.

Pair appeared first in array languages based on the list model, where it also covers the functionality of Promote and Laminate. K, released in the 1990s, defines monadic , as enlist, but dyadic , as catenate. Ambivalent Pair appears in I as ; since 2012; no name is given in the documentation, but the implementation uses "itemize" (the same name as J's Promote) and "cross".

Pair was defined as ⍮ in Extended Dyalog APL in 2018, and then adopted into dzaima/APL. It was added to BQN with the glyph ⋈ in 2021.

Documentation

References

  1. ↑ "Composition and Enclosure" § Composition Operators. SATN-41, 1981-06-20.
  2. ↑ "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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