gnuplot warning: Skipping data file with no valid points, using a very simple file.dat
<p>i'd like to understand the use of "index" command to plot only some groups of datas or for example to plot every group but with different titles etc..</p>

<p>i started with an easy example: in the file prova.dat i have the following text (i've already checked that there are not white records a the end of the lines):</p>

<pre><code>1 1
2 2
3 3
4 4

1 2
2 3
3 4
4 5
</code></pre>

<p>then i use this code to plot data from 'prova.dat':</p>

<pre><code> set term postscript  eps enhanced font 'Times-Roman,24'
 set output 'prova.eps'
 set key right top
 set xrange [1:5]
 set yrange [1:5]
 plot 'prova.dat' index 0 w lines title columnheader(1), \
      'prova.dat' index 1 w lines title columnheader(1) 
</code></pre>

<p>but i get the following warning:</p>

<pre><code>warning: Skipping data file with no valid points
</code></pre>

<p>thus in the .eps produced i have no plots but just the axis (correctly formatted).</p>

<p>i've read also other posts but i can't find a solution.</p>

<p>thank you in advance!</p>