CODEWITHSUNDEEP
pythonmatplotlibplot
Luca
Luca

Reputation: 10996

matplotlib: grouping error bars for each x-axes tick

I am trying to use matplotlib to plot error bars but have a slightly different requirements. So, the setup is as follows:

I have 3 different methods that I am comparing across 10 different parameter setting. So, on the y-axes I have the model fitting errors as given by the 3 methods and on the x-axes, I have the different parameter settings.

So, for each parameter setting, I would like to get 3 error bar plots corresponding to the three methods. Ideally, I would like to plot the 95% confidence interval and also the minimum and maximum for each method for each parameter setting.

Some example data can be simulated as:

parameters = [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7]
mean_1 = [10.1, 12.1, 13.6, 14.5, 18.8, 11.8, 28.5]
std_1 = [2.6, 5.7, 4.3, 8.5, 11.8, 5.3, 2.5]

mean_2 = [10.1, 12.1, 13.6, 14.5, 18.8, 11.8, 28.5]
std_1 = [2.6, 5.7, 4.3, 8.5, 11.8, 5.3, 2.5]

mean_3 = [10.1, 12.1, 13.6, 14.5, 18.8, 11.8, 28.5]
std_3 = [2.6, 5.7, 4.3, 8.5, 11.8, 5.3, 2.5]

I have kept the values same as it does not change anything from the plotting point of view. I see matplotlib.errorbar method but I do not know how to extend it for multiple methods over one single x-axes value as I have in my case. Additionally, I am not sure how to add the [min, max] markers for each of the methods.

Upvotes: 2

Views: 1950

Answers (1)

jkalden
jkalden

Reputation: 1588

Taking your parameters list as x axis, mean_1 as y value and std_1 as errors you can plot an errorbar chart with 

pylab.errorbar(parameters, mean_1, yerr=std_1, fmt='bo')

In case the error bars are not symmetric, i.e. you have lower_err and upper_err, the statement reads

pylab.errorbar(parameters, mean_1, yerr=[lower_err, upper_err], fmt='bo')

The same works with keyword xerr for errors in x direction, which is now hopefully self-explanatory. To show several (in your case 3) different datasets, you can go the following way:

# import pylab and numpy
import numpy as np
import pylab as pl

# define datasets
parameters = [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7]
mean_1 = [10.1, 12.1, 13.6, 14.5, 18.8, 11.8, 28.5]
std_1 = [2.6, 5.7, 4.3, 8.5, 11.8, 5.3, 2.5]

mean_2 = [10.1, 12.1, 13.6, 14.5, 18.8, 11.8, 28.5]
std_2 = [2.6, 5.7, 4.3, 8.5, 11.8, 5.3, 2.5]

mean_3 = [10.1, 12.1, 13.6, 14.5, 18.8, 11.8, 28.5]
std_3 = [2.6, 5.7, 4.3, 8.5, 11.8, 5.3, 2.5]


# here comes the plotting;
# to achieve a grouping, two things are extra here: 
# 1. Don't use line plot but circular markers and different marker color
# 2. slightly displace the datasets in x direction to avoid overlap 
#    and create visual grouping
pl.errorbar(np.array(parameters)-0.01, mean_1, yerr=std_1, fmt='bo')
pl.errorbar(parameters, mean_2, yerr=std_2, fmt='go')
pl.errorbar(np.array(parameters)+0.01, mean_3, yerr=std_3, fmt='ro')
pl.show()

This is about pylab.errorbar, where you have to give the errors explicitly. An alternative approach is to use pylab.boxplot and to prodice a boxplot for each model, but therefore I guess I'll need the full distribution per model per parameter instead of just mean and std.

Upvotes: 2

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