⌿
N⌿Y replicates first-axis cells.
N⌿Y
1 0⌿2 3⍴⍳6 ⍝ 1 3⍴1 2 3
f⌿Y reduces the first axis.
f⌿Y
+⌿2 3⍴⍳6 ⍝ 5 7 9
S f⌿Y starts each lane from the whole seed S on the right.
S f⌿Y
S
10+⌿3 2⍴⍳6 ⍝ 19 22
Counts, identities and [K] follow /.
[K]
/