Square Cup (`⊔`)

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`⊔ 𝕩`: Group Indices

Group the indices of the major cells of 𝕩 by their respective values.

𝕩 must consist of integers. Groups start from 0.

    ⊔ 4‿5‿6‿6‿4‿7‿5

    (↕8) ≍ ⊔ 4‿5‿6‿6‿4‿7‿5

Group the major cells of 𝕩 by their respective indices in 𝕨.

If an element corresponds to ¯1, it is excluded from grouping.

An extra element can be added to the end of 𝕨 to specify length of the result.

    1‿0‿1‿2‿2‿3‿3  ⊔ 4‿5‿6‿6‿4‿7‿5

    1‿0‿1‿¯1‿¯1‿3‿3  ⊔ 4‿5‿6‿6‿4‿7‿5

    1‿0‿1‿¯1‿¯1‿3‿3‿10  ⊔ 4‿5‿6‿6‿4‿7‿5