Axis (with Dyadic Operand) R←Xf[B]Y

f must be a dyadic primitive scalar function, or a dyadic primitive mixed function taken from below. B must be a numeric scalar or vector. X and Y may be any arrays whose items are appropriate to function f. Axis does not follow the normal syntax of an operator.

In most cases, B must be an integer value identifying the axis of X and Y along which function f is to be applied.

Exceptionally, B must be a fractional value for the Laminate function (,) whose upper and lower integer bounds identify a pair of axes or an extreme axis of X and Y. For Take (↑) and Drop (↓), B can be a vector of two or more axes.

⎕IO is an implicit argument of the derived function which determines the meaning of B.

Examples

      1 4 5 =[1] 3 2⍴⍳6
1 0
0 1
1 0

      2 ¯2 1/[2]2 3⍴'ABCDEF'
AA  C
DD  F

      'ABC',[1.1]'='
A=
B=
C=

      'ABC',[0.1]'='
ABC
===

      ⎕IO←O

      'ABC',[¯0.5]'='
ABC
===

Axis with Scalar Dyadic Functions

The axis operator [X] can take a scalar dyadic function as operand. This has the effect of "stretching" a lower rank array to fit a higher rank one. The arguments must be conformable along the specified axis (or axes) with elements of the lower rank array being replicated along the other axes.

For example, if H is the higher rank array, L the lower rank one, X is an axis specification, and f a scalar dyadic function, then the expressions Hf[X]L and Lf[X]H are conformable if (⍴L)←→(⍴H)[X]. Each element of L is replicated along the remaining (⍴H)~X axes of H.

In the special case where both arguments have the same rank, the right one will play the role of the higher rank array. If R is the right argument, L the left argument, X is an axis specification and f a scalar dyadic function, then the expression Lf[X]R is conformable if (⍴L)←→(⍴R)[X].

Examples

      mat
10 20 30
40 50 60

      mat+[1]1 2       ⍝ add along first axis
11 21 31
42 52 62

      mat+[2]1 2 3     ⍝ add along last axis
11 22 33
41 52 63

      cube
 100  200  300
 400  500  600

 700  800  900
1000 1100 1200

      cube+[1]1 2 
 101  201  301
 401  501  601

 702  802  902
1002 1102 1202

      cube+[3]1 2 3
 101  202  303
 401  502  603

 701  802  903
1001 1102 1203

      cube+[2 3]mat
 110  220  330
 440  550  660

 710  820  930
1040 1150 1260

      cube+[1 3]mat
 110  220  330
 410  520  630

 740  850  960
1040 1150 1260