Tetradic . (dmend)

Applies a dyadic verb to a certain value.

Syntax: .[x;y;z;w]

where z is a dyadic verb to be applied, x is a structure to be indexed in depth with a vector index y and w is the second argument of the verb.

o)a:(1 2 3;4 5 6);
o).[a;0 1;+;1]
1 3 3
4 5 6
o)d:`a`b`c!(1 2;3 4;5 6);
o).[d;(`c;1);:;0]
a| 1 2
b| 3 4
c| 5 0
o)t:flip `a`b!(!3;3+!3)
a b
---
0 3
1 4
2 5
o).[t;(`b;0);+;10]
a b
----
0 13
1 4
2 5
o)

For destructive updates use variable symbol:

o)a:(1 2 3;4 5 6); .[`a;0 1;+;1]
`a
o)a
1 3 3
4 5 6
o)