Talk:Sort stability

Why not ask for a stable sort?

Why not just ask for an implementation of a stable sort?
What purpose does it serve to exclude languages that can implement the task as a user routine? --Tinku99 05:08, 7 June 2009 (UTC)

Hi Tinku, Some people, especially those new to a language, might not know too much about the facilities that the language comes with. This task is a comparison of what languages provide rather than what they can be programmed to provide and might be just as useful.
Integer literals, Mutual Recursion, and Common number base formatting are some other tasks that similarly try to contrast the 'native' capabilities of each language. --Paddy3118 09:08, 7 June 2009 (UTC)

J and stability?

Please excuse me, I don't intend to bang on about J, but sorting in ascending order might not be the same thing as a stable sort. The example given in the task description I would say does not sort other columns in ascending order. If the column being sorted on (the second column), has the same values then the relative order of those rows must stay the same. The table has the US and UK Birmingham rows in reverse alphabetical order w.r.t. the first column. A stable sort would leave the US above the UK Birmingham. If J would swap them then it does not do a stable sort. --Paddy3118 20:25, 28 August 2009 (UTC)

Hi Paddy, No problem. It doesn't talk about sorting in ascending order. It says "Elements of /:y that select equal elements of y are in ascending order" - essentially that equal elements will appear in order of appearance.

<lang j> /: 'adfafb' 0 3 5 1 2 4</lang> This is the grade and tells us that to sort the list in ascending order we'd arrange the list by its indices as shown. In this case the equal elements of y are the two a's and the two f's. The a's have indices 0 & 3, the f's have indices 2 & 4. The elements of /:y that select equal elements of y appear in ascending order so the 0 appears before the 3 in the grade and the 2 appears before the 4. Hope that helps! --Tikkanz <lang j> NB. sort txt by txt without the first 4 columns

  txt /: 4&}."1 txt

US Birmingham UK Birmingham UK London US New York </lang>

Thanks Tikkanz for the excellent explanation. --Paddy3118 08:57, 29 August 2009 (UTC)

GAP and stability?

Does GAP seem stable with the example given in the task description? I find it hard to follow what is being described in the GAP example. (Maybe some of the notes would be better off here in the talk page and maybe expanded apon)? --Paddy3118 21:41, 12 June 2011 (UTC)