Re: [Gnuplot-info] How to plot alphabetical data in x-axis

[Lars H. <la...@ho...>]

Hi!

> How can I plot a graph of alphabetical data (for e.g.
> R,H,T) in x-axis vs numerical data in y-axis using
> gnuplot? What will be the format of input file (i.e .dat
> file) ? Can this be done with Gnuplot?

gnuplot is able to read operate with any ASCII-datafile. 
Usually gnuplot supposes, that datapoints in an input-file 
are written in lines, with white spaces as seperator for 
the columns. Other ways can be set. Read "help datafile" 
and its subtopics for more detailled information.

I suppose you want the alphabetical data for the x-axis to 
be sorted. Unfortuanetly gnuplot does not support this 
(yet?). It needs all inputs to be double-precision floats. 
So you have to tell gnuplot, which alphabetical 
character/word belongs to which position on the x-axis.
The simliest way of doing this would be to add a new column 
to your datafile which contains numerical "translations" of 
your alphabetical data and use this column as x-value. 
See "help using" for more information.

Another way might be to sort the lines of your datafile 
externally by the values of the alphabetical data. Then you 
might use the special value "-1" within the using-option, 
which tells gnuplot to use the line number of the datafile 
as x-value. 

As a consequence of the need of numerical input, gnuplot 
automatically marks the tics of the x-axis with numerical 
values. If you would like to change this, you'd have to set 
the tic-markers by hand. "help xtics" tells you how to do 
that.

Regards
Lars


P.S.: I strongly recomend an update to version 4. It should 
be availabe as RPM on the usual file-servers.