/ — Replicate / ReduceN/Y repeats last-axis items by their counts. Boolean counts filter.
1 0 1/10 20 30 ⍝ 10 30
2 1/10 20 ⍝ 10 10 20
Negative counts insert fill. Singleton counts or a singleton axis extend.
1 ¯2/10 20 ⍝ 10 0 0
2/3 4 ⍝ 3 3 4 4
1 0 1/,3 ⍝ 3 3
f/Y reduces the last axis, right-associated. Empty axes use f’s identity.
+/1 2 3 ⍝ 6
-/1 2 3 ⍝ 2
+/⍬ ⍝ 0
N f/Y reduces overlapping windows of width |N|; negative N reverses each window. Width zero uses identities at the 1+≢Y boundaries of a vector.
2+/1 2 3 4 ⍝ 3 5 7
¯2-/1 2 3 ⍝ 1 1
0+/1 2 ⍝ 0 0 0
[K] selects the axis. ⌿ defaults to the first. Float sum/product reductions allow reassociation; generic reductions retain operand order.