Show decimal places and scientific notation on the axis of a matplotlib plot
This is really easy to do if you use the matplotlib.ticker.FormatStrFormatter
as opposed to the LogFormatter
. The following code will label everything with the format '%.2e'
:
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.ticker as mtick
fig = plt.figure()
ax = fig.add_subplot(111)
x = np.linspace(0, 300, 20)
y = np.linspace(0,300, 20)
y = y*1e16
ax.plot(x,y)
ax.yaxis.set_major_formatter(mtick.FormatStrFormatter('%.2e'))
plt.show()
In order to get nicely formatted labels in scientific notation one may use the formatting capabilities of a ScalarFormatter
which uses MathText (Latex) and apply it to the labels.
import matplotlib.pyplot as plt
import numpy as np
import matplotlib.ticker as mticker
fig, ax = plt.subplots()
x = np.linspace(0, 300, 20)
y = np.linspace(0,300, 20)
y = y*1e16
ax.plot(x,y)
f = mticker.ScalarFormatter(useOffset=False, useMathText=True)
g = lambda x,pos : "${}$".format(f._formatSciNotation('%1.10e' % x))
plt.gca().yaxis.set_major_formatter(mticker.FuncFormatter(g))
plt.show()
While this may be useful in a lot of cases, it does not actually meet the requirements of the question. To have equal digits on all labels a more customized version can be used.
import matplotlib.pyplot as plt
import numpy as np
import matplotlib.ticker as mticker
fig, ax = plt.subplots()
x = np.linspace(0, 300, 20)
y = np.linspace(0,300, 20)
y = y*1e16
ax.plot(x,y)
class MathTextSciFormatter(mticker.Formatter):
def __init__(self, fmt="%1.2e"):
self.fmt = fmt
def __call__(self, x, pos=None):
s = self.fmt % x
decimal_point = '.'
positive_sign = '+'
tup = s.split('e')
significand = tup[0].rstrip(decimal_point)
sign = tup[1][0].replace(positive_sign, '')
exponent = tup[1][1:].lstrip('0')
if exponent:
exponent = '10^{%s%s}' % (sign, exponent)
if significand and exponent:
s = r'%s{\times}%s' % (significand, exponent)
else:
s = r'%s%s' % (significand, exponent)
return "${}$".format(s)
# Format with 2 decimal places
plt.gca().yaxis.set_major_formatter(MathTextSciFormatter("%1.2e"))
plt.show()