scan

Scan

f\y
x f\y

scan, also known as cumulative reduce or scanl takes a dyadic function f and reduces an array y using it, while providing an array of intermediate values.

Scan works very similarly to fold.

 +\1 2 3 4 5
1 3 6 10 15
 ,\("ab";1;`d`a`b)
("ab"
 ("a";"b";1)
 ("a";"b";1;`d;`a;`b))

Specifying a left argument x uses it as an initial value.

 3 +\1 2 3 4
4 6 9 13

When used with functions that take more than 2 arguments, scan can take multiple arguments, of which the first one is always the initial value.

 {x,y,z}\["A";1 2 3;"BCD"]
(("A";1;"B")
 ("A";1;"B";2;"C")
 ("A";1;"B";2;"C";3;"D"))