Gnuplot with both color and xtic from data file

Question

I want to make a bar plot, using gnuplot, with values from column 3, xtic labels from column 2, and color from column 4 of my data file. The file looks like:

0   "13 Sep"    2400.18     "blue"
1   "13 Oct"    440.86      "blue"
2   "13 Nov"    867.03      "blue"
3   "13 Dec"    -247.32     "red"
4   "14 Jan"    -3457.56    "red"
5   "14 Feb"    666.94      "blue"

Currently, I plot with the following command,

plot "output.txt" using 1:3:xtic(2) with boxes

and the plot has the correct tic labels in the x-axis and all the bars are colored red. What I would like to do it to get the bar color from the file, or alternatively have a smooth color palette from blue to red, going through white.

I have tried a lot of different suggestions that I've found searching the internet but with no success. How should I do it?

Answer 1

To select a linecolor based on your data, you can use linecolor variable. In that case you must give a line type index as additional column.

Your data file is somewhat redundant. You don't need to have the first column, you have always access to the row number as column(0). The color can be derived from the value sign:

"13 Sep"    2400.18     
"13 Oct"    440.86      
"13 Nov"    867.03      
"13 Dec"    -247.32     
"14 Jan"    -3457.56    
"14 Feb"    666.94     

The script is:

set style fill solid noborder
set xzeroaxis lt -1 lw 2
set boxwidth 0.9 relative
plot "output.txt" using 0:2:($2 < 0 ? 1 : 3):xtic(1) with boxes linecolor variable t ''

with the result (version 4.6.3):

You could also use linecolor rgb variable, linecolor palette etc.

If you want to color the boxes as a mixture of red/blue and white, based on according to their values, you can do it as follows:

set style fill solid border lt -1
set xzeroaxis lt -1 lw 2
set boxwidth 0.9 relative
unset key

stats "output.txt" using 2 nooutput
set palette defined (STATS_min 'red', 0 'white', STATS_max 'blue')
set autoscale cbfix

plot "output.txt" using 0:2:2:xtic(1) with boxes linecolor palette

with the result:

Getting a gradient inside the boxes is more involved and needs some tricking, see Gnuplot vertical gradient on boxes depending of a value?.