gnuplot : using a logarithmic axis for a histogram

Question

I have a data file that I am creating a histogram from.

The data file is :

-0.1  0  0  JANE
1  1  1  BILL
2  2  1  BILL
1  3  1  BILL
6  4  0  JANE
35 5  0  JANE
9  6  1  BILL
4  7  1  BILL
24 8  1  BILL
28 9  1  BILL
9  10  0  JANE
16 11  1  BILL
4  12  0  JANE
45 13  1  BILL

My gnuplot script is :

file='test.txt'
binwidth=10
bin(x,width)=width*floor(x/width)
set boxwidth 1

plot file using (bin($1,binwidth)):(1.0) smooth freq with boxes, \
file using (1+(bin($2,binwidth))):(1.0) smooth freq with boxes

I would like to plot this data on a logscale in y. However there are some 0 values (because some of the bins are empty) that cannot be handled by set logscale y. I get the error Warning: empty y range [1:1], adjusting to [0.99:1.01].

According to gnuplot's help, "The frequency option makes the data monotonic in x; points with the same x-value are replaced by a single point having the summed y-values."

How can I take the log10() of the summed y-values computed by smooth freq with boxes?

Next time please add also a sample data file so that we can test your code without having to generate the data ourselves. — Miguel

Miguel Miguel · Accepted Answer · 2015-09-08T21:03:50

There are at least two things that you could do. One is to use a linear axis between 0 and 1 and then use the logarithmic one as explained in this answer. The other one is to plot to a table first and then set the log scale ignoring the points with zero value.

With a normal linear axis and your code (plus set yrange [0:11]) your data looks:

Now lets plot to a table, then set the log scale, then plot ignoring the zero values:

file='test.txt'
binwidth=10
bin(x,width)=width*floor(x/width)

set table "data"

plot file using (bin($1,binwidth)):(1.0) smooth freq, \
file using (1+(bin($2,binwidth))):(1.0) smooth freq

unset table

set boxwidth 1
set logscale y
set yrange [0.1:11]

plot "data" index 0 using ($1):($2 == 0 ? 1/0 : $2) with boxes lc 1, \
"data" index 1 using ($1):($2 == 0 ? 1/0 : $2) with boxes lc 2

set table sometimes generates some undesirable points in the plot, which you can see at x = 0. To get rid of them you can use "< grep -v u data" instead of "data".

gnuplot : using a logarithmic axis for a histogram

1 Answers