Data disappears when logscale is used in gnuplot

Question

I have successfully made a nice looking histogram in gnuplot with a normal scale but when I add

set logscale y

to my code, the data disappears.

I discovered that logscale does not work with the function I am using to make the histogram (shown in the following link). https://stackoverflow.com/a/2538846/2506689

Does anyone have any suggestions on how to fix this?

mgilson · Accepted Answer · 2013-06-26 13:10:27Z

3

set table to the rescue!

^{Note that I typed all of this into the interactive prompt and copy/pasted my terminal contents. As such, my commands that follow are prefixed by a gnuplot> which you won't include in your script :-)}

First, I generate some data using python ...

import numpy as np
np.savetxt('foobar.txt',np.random.random(1000))

That wasn't hard. Now time to set up gnuplot functions/constants:

gnuplot> binwidth = 0.05
gnuplot> bin(x,width)=width*floor(x/width)
gnuplot> plot 'foobar.txt' using (bin($1,binwidth)):(1.0) smooth freq with boxes

Ok, it works with non-logscale data. That's good. Lets write that data into a separate file using set table

gnuplot> set table 'foobar.table'
gnuplot> plot 'foobar.txt' using (bin($1,binwidth)):(1.0) smooth freq with boxes
gnuplot> unset table

Now I look at the data gnuplot wrote out to see what's there.

gnuplot> !head foobar.table

# Curve 0 of 1, 21 points
# Curve title: "'foobar.txt' using (bin($1,binwidth)):(1.0)"
# x y xlow xhigh type
 0  40  0  0  i
 0.05  57  0.05  0.05  i
 0.1  52  0.1  0.1  i
 0.15  56  0.15  0.15  i
 0.2  49  0.2  0.2  i
 0.25  55  0.25  0.25  i

Unfortunately, it looks like xlow and xhigh are always the same (possible bug?). But that's Ok, we're using a constant binwidth anyway. We'll just use that as the width.

gnuplot> set logscale y
gnuplot> plot 'foobar.table' u 1:2:(binwidth) w boxes

I should note that I've been a little loose with my box positions. To really get it right, you probably need to shift the center of the boxes to the right by half a binwidth:

gnuplot> plot 'foobar.table' u ($1+0.5*binwidth):2:(binwidth) w boxes

answered Jun 26, 2013 at 13:10

mgilson

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4 Comments

Izaak Williamson Over a year ago

That worked perfectly! Thank you. Another question though, how would I make it look more like a square wave/line instead of separate boxes? I use a really narrow box width so it looks more like the area below the plot is shaded with thousands of narrow boxes.

mgilson Over a year ago

I'm not exactly sure that you want, but you could try plot 'foobar.table' u ($1+0.5*binwidth):2:(binwidth) w boxes fs solid noborder or possibly plotting the points w filledcurves.

Izaak Williamson Over a year ago

I want the plot to be 1 line that runs across the top of the boxes (sort of like an irregular square wave) rather than a plot of several boxes side-by-side. Does that make sense?

mgilson Over a year ago

@IzaakWilliamson -- Not sure. There are lots of plot styles that might be what you want. maybe try plotting with lines or with histeps rather than with boxes. (Also, those only take 2 columns of data rather than 3, so it would just be u ($1+0.5*binwidth):2)

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