CODEWITHSUNDEEP
pythonmatplotlib
Joel
Joel

Reputation: 23897

Controlling contour label formatting in pyplot

I'm making a plot where I have contours at [2000, 4000, 6000, 8000]. The contours are labeled as 2000.000, 4000.000 etc. I'd like to get rid of all those trailing zeros. The best option I can find right now is here: http://matplotlib.org/examples/pylab_examples/contour_label_demo.html, which suggests defining a new class for the labels which controls how they are displayed, and then using that class. I've never seen such a convoluted option in python before. Is there no more direct way?

Here is the code provided as an example of defining a class for the labels.

import matplotlib
import numpy as np
import matplotlib.cm as cm
import matplotlib.mlab as mlab
import matplotlib.ticker as ticker
import matplotlib.pyplot as plt

matplotlib.rcParams['xtick.direction'] = 'out'
matplotlib.rcParams['ytick.direction'] = 'out'

##################################################
# Define our surface
##################################################
delta = 0.025
x = np.arange(-3.0, 3.0, delta)
y = np.arange(-2.0, 2.0, delta)
X, Y = np.meshgrid(x, y)
Z1 = mlab.bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0)
Z2 = mlab.bivariate_normal(X, Y, 1.5, 0.5, 1, 1)
# difference of Gaussians
Z = 10.0 * (Z2 - Z1)

##################################################
# Make contour labels using creative float classes
# Follows suggestion of Manuel Metz
##################################################
plt.figure()

# Basic contour plot
CS = plt.contour(X, Y, Z)


# Define a class that forces representation of float to look a certain way
# This remove trailing zero so '1.0' becomes '1'
class nf(float):
    def __repr__(self):
        str = '%.1f' % (self.__float__(),)
        if str[-1] == '0':
            return '%.0f' % self.__float__()
        else:
            return '%.1f' % self.__float__()

# Recast levels to new class
CS.levels = [nf(val) for val in CS.levels]

# Label levels with specially formatted floats
if plt.rcParams["text.usetex"]:
    fmt = r'%r \%%'
else:
    fmt = '%r %%'
plt.clabel(CS, CS.levels, inline=True, fmt=fmt, fontsize=10)

Upvotes: 1

Views: 4712

Answers (1)

filippo
filippo

Reputation: 5294

The fmt parameter can be either a classic format string or a callable that converts a scalar to a string.

If you don't have fancy requirements you could just pass fmt='%d' instead of a custom class.

For common formats you should be also able to resort to the default formatters in matplotlib.ticker before having to implement your own.

Upvotes: 3

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