Partitioned Enclose
⊂
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Partitioned Enclose (⊂) is a dyadic function which splits its right argument into differently sized pieces as determined by the left argument.
Basic functionality
In the simplest case, and on a vector right argument, the corresponding element in the left argument indicates where divisions begin: <syntaxhighlight lang=apl>
1 0 1 0 0 0 0⊂'HiEarth'
┌──┬─────┐ │Hi│Earth│ └──┴─────┘ </source>
Non-Boolean left argument
Almost all dialects restrict the left argument to provide only the above functionality. However, the left argument can be interpreted as a count of how many partitions begin with a particular position: <syntaxhighlight lang=apl>
2 0 3 0 0 0 0⊂'HiEarth'
┌┬──┬┬┬─────┐ ││Hi│││Earth│ └┴──┴┴┴─────┘ </source>
Short left argument
The dialects that support this extension also allow omission of trailing zeros, which is useful if the partitioning vector is generated by where's inverse: <syntaxhighlight lang=apl>
⍸⍣¯1⊢1 1 3 3 3
2 0 3
2 0 3⊂'HiEarth'
┌┬──┬┬┬─────┐ ││Hi│││Earth│ └┴──┴┴┴─────┘ </source>
Long left argument
Additional trailing empty divisions are created by adding an additional division count corresponding to the position beyond the end of the right argument: <syntaxhighlight lang=apl>
1 0 1 0 0 0 0 1⊂'HiEarth'
┌──┬─────┬┐ │Hi│Earth││ └──┴─────┴┘ </source>
Split into lengths
This above extensions allow a simple definition of a split-into-lengths function:
Try it online! <syntaxhighlight lang=apl>
Split←{⍵ ⊂⍨ ⍸⍣¯1 +\ ¯1↓1,⍺}
3 3 4 Split 'HowAreYou?'
┌───┬───┬────┐ │How│Are│You?│ └───┴───┴────┘ </source>