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Re: Multi-column sort [message #79457 is a reply to message #79404]

Mon, 05 March 2012 02:53

Percy Pugwash
Messages: 12
Registered: January 2012

Junior Member

Thanks very much. I had looked at Craig Markwardt's multisort, but it didn't quite do what I wanted (the number of columns to sort by was limited and could not easily be changed at run-time).

I've not looked at bsort yet, but will have a look, thanks. My only concern is that I'm aware that bubble sort is usually much slower than quicksort, which I believe sort() uses... Might still be worth it though.

The solution I came up with is below, in case anyone is interested. Please bare in mind that it has not been properly tested, but seems to be working.

P

function sort_strcolumns, strtable, indices
maxlen = max(strlen(strtable[abs(indices),*]))
ncols = n_elements(indices)
nrows = (size(strtable,/dim))[1]
sortlist = reform(string(strtable[abs(indices),*],f='(a-'+string(maxlen ,f='(i0)')+')'),ncols,nrows,/overwrite)
sortlist = reform(byte(sortlist),maxlen*ncols,nrows,/overwrite)
for i=0,n_elements(indices)*maxlen-1 do sortlist[i,*] *= (-1)^(indices[i/maxlen] lt 0)
return, sort(string(sortlist))
end

On Friday, 2 March 2012 12:26:00 UTC, Gianguido Cianci wrote:
> Firstly, sort() does not maintain the order of identical elements so I'd use bsort() which you can find online somewhere, can't remember where... I believe it has a /reverse or /invert option, not at my computer right now.
>
> Secondly, you should bsort columns in increasing order of importance, with the most important sort last.
>
> I have a dumb for-loop procedure that does that. This requires multiple searches through the array, which might not be optimal, but once you write it, you'll never use sort instead of bsort again :-)
>
> G

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[Message index]

		Multi-column sort By: Percy Pugwash on Thu, 01 March 2012 07:02
		Re: Multi-column sort By: Percy Pugwash on Mon, 05 March 2012 02:59
		Re: Multi-column sort By: Brian Wolven on Mon, 05 March 2012 09:54
		Re: Multi-column sort By: Percy Pugwash on Mon, 05 March 2012 02:53
		Multi-column sort By: cgguido on Fri, 02 March 2012 04:26
		Re: Multi-column sort By: wlandsman on Thu, 01 March 2012 14:02

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