## Symbols for sort idioms

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### Re: Symbols for sort idioms

Thanks for a lot of interesting presentation & discussion in the conf last week .

I was very slow in implementing ` sort in CoSy because I so wanted ` grade .

Finally , I figured out how to append iota to the list to be sorted to be carried along during the sort , built on Helmar Wodke's terse algorithm , http://cosy.com/4thCoSy/Code/CoSy/sort.f . ( It needs to be revisited because it is not order preserving for equals . )

I've found no way to get the ` grade `w/o doing the sort . If there is , please enlighten me .

So I agree ` sort should have been and be a primitive . I'm surprised the inefficiency of having to go around the grade > index ring to retrieve the sort survived the early years of APL .

I'm taking the liberty of showing the coded for ` nub and ` group which are at about line 1580 in http://cosy.com/4thCoSy/Code/CoSy/CoSy.f .

Code: Select all
`| return unique items .  Like  K's  ' ? : nubb 1p> R@ ['] where 'R ,/ R@ rho iota =i 1P> ; | bool of 1st occurances: nubx nubb & ;    | indices of 1st occurences : nub 1p> dup nubx at 1P> ;    | unique items .: nnub 1p> dup nubb 0=i & at 1P> ; | redundants | Group items by uniques | see Wed.Oct,20191002 | https://youtu.be/fxx9kS_seXk |: grpib 1p> nub R@ ,/ ['] =i 'L 1P> ;    | group integer bool: grpix grpib ['] & 'm ;        | group integer index : grpcx >a> nub a> swap  ' conn 'R  ;   | 20191008 | ` nubgrp optimized merge . Eliminates redundant call of ' nub : nubgrpib 1p> nub >a> R@ ,/ ['] =i 'L a> swap ,L 1P> ; | nub & group integer bool| and uses CoSy's access to addresses using ' ix rather than just ' i@ and ' i!| to optimally replace just the second item in the result from ' nubgrpib: nubgrpix nubgrpib >a> 1 ix dup @ ['] & 'm swap rplc a> ; : nubgrpcx >a> nub a> swap >a> ' conn 'R a> swap ,L  ;    | 20210625 | /\ | Takes list . Returns 2 item list of `( nub grp )` . | ( L R  --  nub sums ,L ): aggr nubgrpcx >a> 1th { at +/ } 'R a> dsc swap ,L ; | aggregate ( sum ) values L by nub of R . | 20210705 | `

` nub and ` group are a similar situation where you can't do the ` group w/o doing the nub . So you can save some work by having a word which returns both together .

Bob Armstrong

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