[GRASS-user] List of existing values

[Nikos Alexandris]

Martin Landa wrote:
> > > > as mentioned in Hamish's response, use combination of
> > > > `sort` and `uniq`
> > > > r.starts -1 input=data | sort | uniq
 
Nikos:
> > > shorter:
> > > r.starts -1 input=data | sort -u

Hamish:
> > AFAIR, those are not the same thing and can not be used
> > interchangeably. (although I don't fully remember why right now)

Nikos: 
> It has troubled me as well (now and in the past). I did (before posting the
> above) a quick test using a column from a vector map containing strings. I
> counted the result from both "uniq" and "sort -u" with "| wc -l". The
> results were identical.
> 
> So... :-? Maybe it is ok for strings/integers(?). One should be more
> careful with those "knifes".

Hamish: 
> > anyway, for floating point maps I still think it's a bad idea.
> > 
> > I'm sure there is a Python equivalent of 'sort|uniq', but don't
> > know what it is.
> > 
> > 'sort' and 'uniq' are UNIX command line power tools and not
> > available in MS Windows. But.. the MSys command prompt that
> > ships with WinGrass supplies them and you can use them there.
> > I suppose the "bin" dir where they are kept are not part of the
> > gui's PATH which is why they wouldn't work from the Cmd> gui
> > prompt.

Here some details from "(coreutils.info.gz)sort invocation":

--%<---
`-u'
`--unique'
     Normally, output only the first of a sequence of lines that compare
     equal.  For the `--check' (`-c' or `-C') option, check that no
     pair of consecutive lines compares equal.

     This option also disables the default last-resort comparison.

     The commands `sort -u' and `sort | uniq' are equivalent, but this
     equivalence does not extend to arbitrary `sort' options.  For
     example, `sort -n -u' inspects only the value of the initial
     numeric string when checking for uniqueness, whereas `sort -n |
     uniq' inspects the entire line.  *Note uniq invocation::.
--->%--

Nikos