`∩` — Duplicates / Intersection

Function. Keys: Alt-c. Ranks: ∞ monadic, ∞ ∞ dyadic

∩Y keeps the distinct major cells of Y that occur more than once, in order of first appearance. It matches cells as ∪ does.

∩"mississippi"      ⍝ "isp"
∩3 1 3 3 2 1        ⍝ 3 1

X∩Y keeps the major cells of X found among the major cells of Y. Order and repetitions are retained. Uses tolerant matching.

1 2 1 3∩1 3        ⍝ 1 1 3
"abcd"∩"bdf"        ⍝ "bd"
[1 2⋄3 4⋄1 2]∩[1 2⋄5 6] ⍝ [1 2⋄1 2]

Errors