Partition

⊆ ⊂

Partition (⊆, ⊂) is a dyadic function which splits its right argument into differently sized pieces as determined by the non-negative integer left argument. This article uses ⊆ to distinguish Partition from Partitioned Enclose (which is always ⊂), but the actual glyph used varies by dialect.

On a vector right argument, the arguments must have the same length with each element in the left argument corresponding to an element in the right argument. Partition begins a new division of its right argument whenever a left argument element is greater than its neighbour on the left (with a 0 assumed to the left of the first element):

Try it online!

      1 1 2 2 2 2 2⊆'HiEarth'
┌──┬─────┐
│Hi│Earth│
└──┴─────┘

Works in: Dyalog APL

Right argument elements can be skipped by having their corresponding left argument element be 0:

      1 1 2 2 2 0 0⊆'HiEarth'
┌──┬───┐
│Hi│Ear│
└──┴───┘

Works in: Dyalog APL

In the case where the left argument is Boolean, Partition splits its right argument on runs of 0s in the left argument, allowing a very short split-on-delimiter function:

Try it online!

      1 1 1 0 1 1 1 0 1 1 1 1⊆'How are you?'
┌───┬───┬────┐
│How│are│you?│
└───┴───┴────┘
      ' '(≠⊆⊢)'How are you?'
┌───┬───┬────┐
│How│are│you?│
└───┴───┴────┘

Works in: Dyalog APL

External links

Tutorials

• APL Cultivation

Documentation

• Dyalog
• APLX