Getting gnuplot to put bars side-by-side - gnuplot

Question

I have the following gnuplot script:
set autoscale
unset log
unset label
unset term
unset output
set xtics rotate by -90
set ytic auto
unset title
set xlabel "Survey metadata attribute subset"
set ylabel "Accuracy of classifier (%)"
set boxwidth 0.1
set style fill solid
set term eps
set output "metadata.eps"
plot "metadata.dat" using 1:3:xtic(2) title "PART" with boxes, \
"metadata.dat" using 1:5:xtic(2) title "JRip" with boxes, \
"metadata.dat" using 1:7:xtic(2) title "FURIA" with boxes
However, this draws all 3 sets of bars on top of each other, while I want them side by side, in that order, grouped together. So it should go something like: PARTbar, JRipbar, FURIAbar, gap, PARTbar, JRipbar, FURIAbar, gap, etc. How would I go about doing this?

Answer 1

I guess what you want is set style histogram clustered.
I have taken a minimal dataset (see bottom) graphing it with
set style histogram clustered
set xtics rotate by -90
unset title
set xlabel "Survey metadata attribute subset"
set ylabel "Accuracy of classifier (%)"
set boxwidth 1
set style fill solid
set term png
set output "so.png"
plot [-0.5:2.75][1:17] "so.dat"using 3:xtic(2) title "PART" with histograms, \
"" using 4 title "JRip" with histograms, \
"" using 5 title "FURIA" with histograms
which yields
I think you can take it further from here.
Data file "so.dat":
1 a 10 12 15
2 b 12 14 16
3 c 11 15 14

Answer 2

Suppose your data looks like this
1 a 2 3 4
2 b 1 4 5
3 c 6 7 8
One option is to set the boxwidth smaller and manually adjust the box positions so that they line up.
We can do that with
set boxwidth 0.25
plot datafile using ($1-0.25):3 with boxes t "First Series", \
"" using 1:4:xtic(2) with boxes t "Second Series", \
"" using ($1+0.25):5 with boxes t "Third Series"
This results in the following graph
Notice that I only set the xtics on the second series (the one in the middle), and I subtracted the boxwidth from the first series x coordinate (moving it back by one box unit), and added this to the last series (moving it forward by one box unit). I choose to use a boxwidth of 0.25 instead of 0.33 to allow a little gap between groups. Putting the xtic only on the second series ensures that it is on the one in the middle. With more boxes you will use a different width and will have to determine on which one to set the xtic labels.
An alternative is to use the histogram style. With the default boxwidth of 1, you can do
plot datafile u 3 with histogram t "First Series", \
"" u 4:xtic(2) with histogram t "Second Series", \
"" u 5 with histogram t "Third Series"
In this case, it doesn't matter where you place the xtic specification.
The histogram styles are very complex having lots of options. Essentially it consists of multiple plotting styles that are all invoked with the with histogram specification.
Which one of these methods to choose is mostly a matter of personal preference. The first is how you'd do this before the histogram style was added. The box method gives you more manual control over the final result, but the histogram style automates a lot of the details of getting those boxes just right.