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You can assign a value to a variable with the glyph: '←'.
{{Built-in|Assignment|←}} allows associating a name with an [[array]] value. Some dialects also allow assignment of function and operator values using the assignment arrow. In [[defined functions]], assignment is global by default, but can be made local through explicit mention of the target name in the function header, or through dynamic [[shadow]]ing using <syntaxhighlight lang=apl inline>⎕SHADOW</syntaxhighlight>. In [[dfn]]s, assignments are local by default, but can be made global by explicit mention of the target namespace. Modified/indexed/selective assignment updates the most local definition.
==Examples==
===Basic usage===
Common examples (boxing on, and [[index origin]] is 0):
<syntaxhighlight lang=apl>
      ⎕←mat←(1 2 3)(1 2 3)
┌─────┬─────┐
│1 2 3│1 2 3│
└─────┴─────┘
</syntaxhighlight>
===Indexed assignment===
Individual elements can be updated using index assignment:
<syntaxhighlight lang=apl>
      mat[0]←1
      mat
┌─┬─────┐
│1│1 2 3│
└─┴─────┘
</syntaxhighlight>
A semicolon is necessary when dealing with a [[matrix]]:
<syntaxhighlight lang=apl>
      mat←3 3⍴⍳9
      mat
0 1 2
3 4 5
6 7 8
      mat[0 1;]
0 1 2
3 4 5
      mat[0 1;0 1]←0
      mat
0 0 2
0 0 5
6 7 8
</syntaxhighlight>
For higher-[[rank]] arrays, the number of semicolons needed is one less than the array rank.
===Modified assignment===
Some dialects allow placing a function the the immediate left of the assignment arrow:
<syntaxhighlight lang=apl>
      var←42
      var+←1
      var
43
</syntaxhighlight>
<syntaxhighlight lang=apl inline>var+←1</syntaxhighlight> is essentially equivalent to <syntaxhighlight lang=apl inline>1⊣var←var+1</syntaxhighlight> except that the result is [[shy]].
===Modified indexed assignment===
Modified assignment can also be combined with indexed assignment:
<syntaxhighlight lang=apl>
      mat←3 3⍴0
      mat
0 0 0
0 0 0
0 0 0
      mat[0 1;1]+←1
      mat
0 1 0
0 1 0
0 0 0
      mat[1;1],←'x'
      mat
0 1 0
0 x 0
0 0 0
</syntaxhighlight>
== External Links ==


Common examples (boxing on, and ⎕io is 0):
=== Documentation ===
    mat←(1 2 3)(1 2 3)
 
    mat
* [https://help.dyalog.com/latest/index.htm#Language/Primitive%20Functions/Assignment.htm Dyalog]
┌─────┬─────┐
* [https://microapl.com/apl_help/ch_020_010_110.htm APLX]
│1 2 3│1 2 3│
* J: [https://code.jsoftware.com/wiki/Vocabulary/eqdot local], [https://code.jsoftware.com/wiki/Vocabulary/eqco global]
└─────┴─────┘
{{APL built-ins}}[[Category:Primitive functions]]
    mat[0]←1  ⍝ indexed assignment
    mat
┌─┬─────┐
│1│1 2 3│
└─┴─────┘
    mat←3 3⍴⍳9
    mat
0 1 2
3 4 5
6 7 8
    mat[0 1;] ⍝ 1 semicolon is necessary when dealing with 2D arrays, 2 semicolons for 3D arrays etc.
0 1 2
3 4 5
    mat[0 1;0 1]←0
    mat
0 0 2
0 0 5
6 7 8
    ⍝ incrementing (or any dyadic function) parts of an array
    mat←3 3⍴0
    mat
0 0 0
0 0 0
0 0 0
    mat[0 1;1]+←1
    mat
0 1 0
0 1 0
0 0 0
    mat[1;1],←'x'
    mat
0 1 0
0 x 0
0 0 0

Revision as of 22:12, 10 September 2022

←

Assignment (←) allows associating a name with an array value. Some dialects also allow assignment of function and operator values using the assignment arrow. In defined functions, assignment is global by default, but can be made local through explicit mention of the target name in the function header, or through dynamic shadowing using ⎕SHADOW. In dfns, assignments are local by default, but can be made global by explicit mention of the target namespace. Modified/indexed/selective assignment updates the most local definition.

Examples

Basic usage

Common examples (boxing on, and index origin is 0): 

      ⎕←mat←(1 2 3)(1 2 3)
┌─────┬─────┐
│1 2 3│1 2 3│
└─────┴─────┘

Indexed assignment

Individual elements can be updated using index assignment: 

      mat[0]←1
      mat
┌─┬─────┐
│1│1 2 3│
└─┴─────┘

A semicolon is necessary when dealing with a matrix: 

      mat←3 3⍴⍳9
      mat
0 1 2
3 4 5
6 7 8
      mat[0 1;]
0 1 2
3 4 5
      mat[0 1;0 1]←0
      mat
0 0 2
0 0 5
6 7 8

For higher-rank arrays, the number of semicolons needed is one less than the array rank.

Modified assignment

Some dialects allow placing a function the the immediate left of the assignment arrow: 

      var←42
      var+←1
      var
43

var+←1 is essentially equivalent to 1⊣var←var+1 except that the result is shy.

Modified indexed assignment

Modified assignment can also be combined with indexed assignment: 

      mat←3 3⍴0
      mat
0 0 0
0 0 0
0 0 0
      mat[0 1;1]+←1
      mat
0 1 0
0 1 0
0 0 0
      mat[1;1],←'x'
      mat
0 1 0
0 x 0
0 0 0

External Links

Documentation

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
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
Dyadic Bind ∙ Compositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner Product ∙ Determinant ∙ Power ∙ At ∙ Under ∙ Rank ∙ Depth ∙ Variant ∙ Stencil ∙ Cut ∙ Direct definition (operator)
Quad names Index origin ∙ Comparison tolerance ∙ Migration level ∙ Atomic vector
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