Re: [Bug-apl] Help with APL expression

[Louis de Forcrand]

Is it important that they be grouped in the order specified by the key?

If not, this should do (with C the categories and S the strings):

(⊂[1]C∘.=∪C)/¨⊂S

If they must be ordered, then this can do it:

(⊂[1]C∘.=U[⍋U←∪C])/¨⊂S

In addition, the categories don’t have to be numbers.

Note that Dyalog’s (dyadic) key function is equivalent to this, with L being

the operator’s left operand:

L¨(⊂[1]C∘.=∪C)/¨⊂S

Cheers,

Louis

On 05 Jul 2017, at 11:43, Elias Mårtenson <address@hidden> wrote:

I have a list of strings, and a corresponding set of categorisations:

      strings ← 'foo' 'bar' 'abc' 'def' 'ghi' 'jkl'

      categories ← 1 1 0 2 1 0

I now need to group these strings according to category. In other words, when applying operation X, I need the following output:

      categories X strings

┏→━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓

┃┏→━━━━━━━━━━┓ ┏→━━━━━━━━━━━━━━━━┓ ┏→━━━━┓┃

┃┃"abc" "jkl"┃ ┃"foo" "bar" "hgi"┃ ┃"def"┃┃

┃┗∊━━━━━━━━━━┛ ┗∊━━━━━━━━━━━━━━━━┛ ┗∊━━━━┛┃

┗∊∊━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛

What is the best way to solve this?