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⊂ — Enclose / Partitioned enclose

Function. Keys: Alt-z. Hanzi: 包. Ranks: ∞ monadic, 1 ∞ dyadic

⊂Y is a scalar holding Y.

A one-item bracket list, [Y], is a vector, not a scalar. ⊂ cannot enclose a function, because ⊂ next to a function forms a train. To enclose a function, write ᵘ after it. fᵘ is a scalar holding f.

⍴⊂1 2 3            ⍝ ⍬ₓ
↑⊂1 2 3            ⍝ 1 2 3
⊂3 ≡ 3             ⍝ $f

With axes, ⊂⍠K Y encloses cells on axes K.

⊂₁2 3⍴⍳6ₓ          ⍝ [[0 1 2] [3 4 5]]ₓ

N⊂Y starts partitions at positive marks along the leading axis. Each partition is a block of major cells. Leading zero marks are ignored.

1 0 1 0⊂"abcd"     ⍝ "ab" "cd"
1 0 1⊂3 2⍴⍳6ₓ       ⍝ [[0 1⋄2 3] [4 5⋄]]ₓ

A mark greater than 1 starts extra empty partitions. Unit marks extend. N⊂⍠K Y partitions along axis K instead. N⊂⍤1 Y partitions each row.

1 0 1⊂₁2 3⍴⍳6ₓ       ⍝ [[0 1⋄3 4] [[2]⋄[5]]]ₓ
1 0 1⊂⍤1 (2 3⍴⍳6ₓ)  ⍝ [[0 1] [2]⋄[3 4] [5]]ₓ

See also ⊆.

Inverse

⊂⁻Y is ↑Y. X⊂⁻Y joins the parts Y. Partitioning the result by X must give Y again, so X can’t drop leading items.

⊂⁻⊂1 2             ⍝ 1 2
1 0 1⊂⁻(1 2⋄3)   ⍝ 1 2 3