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Re: Advanced Sorting - GRT - Guttman Rosler Transform

by dws (Chancellor)
on Feb 15, 2002 at 21:14 UTC ( #145767=note: print w/replies, xml ) Need Help??


in reply to Advanced Sorting - GRT - Guttman Rosler Transform

The basic idea is to encode the precomputed keys into a string, usually using pack() such that perl can sort them lexicographically

This is a key point. I've seen it overlooked in two cases, both leading to subtle sorting problems of the "well, this stuff sorts most of the time" variety.

A naive read of Guttman-Rosler is "hey, let's cram the key parts together in a way we can uncram them later." That's necessary, but not sufficient. Simple concatenation won't do. You must pack(), or concatenate in such a way that the keys are aligned for a lexicographic sort. If you see someone use join in a Guttman-Rosler search, watch out!

Consider the difference between

Naive join Aligned keys foo 47 foo 47 foo 103 foo 103
If you don't align the keys (typically via pack or a carefully crafted sprintf), you risk getting composite keys that sort correctly most of the time. A variant of the problem can occur with non-numeric strings when joining them with a character like '|'.

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[Discipulus]: if is the author of a patch, is more like a 'request to push' into rather than a pull request..
[choroba]: as it's considered unpolite to push to someone else's repo
[choroba]: and in fact, you don't push into the target repo, you push into your branch of your fork
[choroba]: the maintainer of the upstream repo than "merges" the pull request, i.e. they pull from your fork into the upstream
[Discipulus]: ' i.e. you asked them to pull from your repo' =~ I (subj) want to push
[Discipulus]: chorobayour words are reasonable
[choroba]: I'm just repeating some else's words as I remembered them after having asked the same question
[choroba]: s/some/someone/
Discipulus what a pity all people do not speak only in eatalian..

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