When you have a columns and want to sort by multiple columns in various orders - you will start chaining reverses

my jq sort_by is stable, but if i need to sort by descending - I have to do double reverse, which i dont like

sort_by(.person) # first sort in ascending
| reverse | sort_by(.city) | reverse # then sort by in descending

In order to keep both city descending and person ascending, (but by city) - I feel like I need double reverse, so this api does not looks good, in terms of performance for advanced sorting.

Do you know any workaround, not using double reverse?

CodePudding user response：

More of an idea than a good solution, but you could sort by negative codepoints obtained by using explode. At least there's no reverse involved, and only one call to sort_by is needed for all criteria.

sort_by(.person, (.city | [-explode[]]))

CodePudding user response：

Quicksort is not stable, but ...

def reverse_quicksort_by(f):
  def r:
    if length < 2 then .
    else (.[0]|f) as $pivot
    | reduce .[] as $x
        # state: [less, equal, greater]
        ( [ [], [], [] ];
        ($x|f) as $y
        | if   $y  < $pivot then .[0] = [$x]   .[0]  # add x to less
          elif $y == $pivot then .[1]  =  [$x]       # add x to equal
          else  .[2] = [$x]   .[2]                   # add x to greater
          end )
      | (.[2] | r )    .[1]   (.[0] | r )
    end ;
  r;

This has been tested with both the C and Go implementations (jq and gojq).