/ — 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
Reduction returns the accumulator. An unseeded one-item reduction returns that item. Unreduced axes supply the result frame.
,/⊂2 3 ⍝ 2 3
,/,⊂2 3 ⍝ 2 3
+/⊂⊂3 ⍝ ⊂3
S f/Y starts from seed S on the right: S f/a b c is a f b f c f S. Empty reductions return the seed. Each lane uses the whole seed.
10 -/1 2 3 ⍝ ¯8
10 +/2 3⍴⍳6 ⍝ 16 25
(⊂10)+/1 2 3 ⍝ ⊂16
10 20 (+/⍤0 1)2 3⍴⍳6 ⍝ 16 35
Nested paths use seeded Pick reduction.
tree←(10 20⋄ 30 (40 50))
tree⊃/⌽2 2 1 ⍝ 40
Use full windows for moving reductions.
+/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.