f may be any dyadic function which returns an explicit result. Y may be any array whose items are appropriate to function f. X must be the name of an existing array. EXP is an expression that selects elements of X. (See Assignment (Selective) for a list of allowed selection functions.) The selected elements of X must be appropriate to function f.
Y is either an array of the same shape as the selected elements of X or a scalar that is notionally extended to be the same shape as the selection.
The operator loops through the selected elements of X in ravel order. For each selected element X[i], it calculates the result of X[i]fY[i] and assigns it back to the same element X[i].
R is the "pass-through" value, that is, the value of Y. If the result of the derived function is not assigned or used, there is no explicit result.
Example
A 12 36 23 78 30 ((A>30)/A) ×← 100 A 12 3600 23 7800 30
As the operator performs a loop, if an element of X is selected more than once, function f will be applied the corresponding number of times and successively to the same element of X.
a←3⍴0
(5⍴a)+←1
a
2 2 1