Difference between revisions of "From"

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(extension)
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bdace
 
bdace
 
</source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}}
 
</source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}}
 +
== Potential extension ==
 +
Select can be defined as <source lang=apl inline>⌷⍨∘⊃⍨⍤0 ∞</source> thus allowing both the above usage and "scatter point indexing":
 +
<source lang=apl>
 +
      1 4 3 ⊇ 4 4⍴⎕A
 +
ABCD
 +
MNOP
 +
IJKL
 +
      (1 1)(4 4)(3 4) ⊇ 4 4⍴⎕A
 +
APL
 +
</source>
 
{{APL built-ins}}
 
{{APL built-ins}}

Revision as of 10:51, 22 April 2020

⊇

Select (⊇) (jokingly referred to as Sane Indexing) is a primitive function that allows selecting multiple major cells using indices of the cells. It is equivalent to ⌷⍨∘⊂⍨ and ⌷⍤0 ∞, only providing a neater notation for such a fundamental concept. It was introduced in Extended Dyalog APL, and then adopted into dzaima/APL.

Common usage

Select is commonly used to reorder the major cells of an array. For example, the following shuffles any array into random order:

Try it online!

      Shuffle←?⍨∘≢⊇⊢
      Shuffle 'abcdef'
fbdcea
Works in: dzaima/APL, Extended Dyalog APL

Without Select, one would have to write Shuffle←⊢⌷⍨∘⊂?⍨∘≢.

In a case where the left argument is a permutation vector for the right argument, the functionality can rightfully be called Permute.

Select especially cleans up expressions for reordering. An ascending sort can be represented as ⍋⊇⊢ and "sort by" can be written as ⊇⍨∘⍋:

Try it online!

      'abcde' ⊇⍨∘⍋ 3 1 4 1 5
bdace
Works in: dzaima/APL, Extended Dyalog APL

Potential extension

Select can be defined as ⌷⍨∘⊃⍨⍤0 ∞ thus allowing both the above usage and "scatter point indexing": 

      1 4 3 ⊇ 4 4⍴⎕A
ABCD
MNOP
IJKL
      (1 1)(4 4)(3 4) ⊇ 4 4⍴⎕A
APL
APL built-ins [edit]
Primitive functions
Scalar
Monadic Conjugate ∙ Negate ∙ Signum ∙ Reciprocal ∙ Magnitude ∙ Exponential ∙ Natural Logarithm ∙ Floor ∙ Ceiling ∙ Factorial ∙ Not ∙ Pi Times ∙ Roll ∙ Type ∙ Imaginary ∙ Square Root
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 ∙ Select ∙ Replicate ∙ Expand ∙ Set functions (Intersection ∙ Union ∙ Without) ∙ Bracket indexing ∙ Index
Selector Index generator ∙ Grade ∙ Index Of ∙ Interval Index ∙ Indices ∙ Deal
Computational Match ∙ Not Match ∙ Membership ∙ Find ∙ Nub Sieve ∙ Encode ∙ Decode ∙ Matrix Inverse ∙ Matrix Divide ∙ Format ∙ Execute ∙ Materialise ∙ Range
Primitive operators Monadic Each ∙ Commute ∙ Constant ∙ Replicate ∙ Expand ∙ Reduce ∙ Windowed Reduce ∙ Scan ∙ Outer Product ∙ Key ∙ I-beam ∙ Spawn ∙ Function axis
Dyadic Bind ∙ Compositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner Product ∙ Power ∙ At ∙ Under ∙ Rank ∙ Depth ∙ Variant ∙ Stencil ∙ Cut (J)
Quad names
Arrays Index origin ∙ Migration level ∙ Atomic vector
Functions Name class ∙ Case convert ∙ Unicode convert
Operators Search ∙ Replace
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