@
At r←[x]({Fn}@m)y
If x
is provided, the left operand must be a function.
r
is the result of substituting cells of y
that appear in m
with elements provided by F
or n
: if n
is provided, it must have the same shape as y
or one less rank and same trailing shape, and corresponding elements in n
are used from m
, or the whole of n
if it is of lower rank; if F
is provided, it is called with each cell of y
matching m
and optionally x
.