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How can I perform the equivalent of M-x sort-columns with a stable sort?

For example, let's say my text is:

a 99
b 98
b 97
a 96
a 95
b 94
a 93
b 92
c 91
...

And I want to perform a stable sort against the first column.

With sort-columns I would put mark at the beginning of the buffer, put point in the last line just after the first column, and M-x sort-columns RET.

My problem is that this sort is not stable. The output is:

a 93
a 95
a 96
a 99
b 92
b 94
b 97
b 98
c 91

Whereas I need to keep the line order for each first column:

a 99
a 96
a 95
a 93
b 98
b 97
b 94
b 92
c 91

How could I do that? Is there a hidden option in sort-columns? Or is some Elisp necessary? I know sort --stable could do the trick but I want a solution that works on Windows where the sort command-line tool is absent.

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I think that sort-fields does what you want. At least it does so with the example text you show.

See also the Elisp manual, node Sorting.

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  • "sort-fields" doesn't seem documented as being a stable sort, though in practice it looks like it is. So it might stop being stable in the next Emacs releases?
    – fbauzac
    Commented May 6, 2019 at 12:58
  • Yes, presumably so. But it's been the way it is for many decades. Please consider sending an enhancement request to document that it is a stable sort (and thus have Emacs commit to that), using M-x report-emacs-bug.
    – Drew
    Commented May 6, 2019 at 13:37

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