format axis ticks using TickFormatters in matplotlib

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matplotlib_format_axis_ticks

Skill - Format axis ticks using TickFormatters in matplotlib

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Skills Required

Please make sure to have all the skills mentioned above to understand and execute the code mentioned below. Go through the above skills if necessary for reference or revision

Matplotlib is a plotting library tn the scipy ecosystem of libraries.

Please make sure that you covered thepost on basics

Sometimes we want to explicitly control the formatting of ticks like number of decimal places, date formats etc. This can be done through TickFormatters

Control axis tick labels with format string using ‘StrMethodFormatter’

import matplotlib.pyplot as plt
import matplotlib as mpl
x = [0,1,2,3,4,5,6,7,8]
y = [8,6,4,2,9,7,6,3,1]

# create a plotting area and get the figure, axes handle in return
fig, ax = plt.subplots()

# plot data on the axes handle
ax.plot(x, y)

# set x axis major ticks format as 2 decimal places
ax.xaxis.set_major_formatter(mpl.ticker.StrMethodFormatter('{x:0.2f}'))

# print the plot
plt.show()

matplotlib_strmethod_formatter_demo

Control axis tick labels text with user defined function using ‘FuncFormatter’

FuncFormatter should be supplied with a function that takes in tick value and tick position and outputs the tick label string

import matplotlib.pyplot as plt

x = [0,10000,20000,30000,40000,50000,60000,70000,80000]
y = [8,6,4,2,9,7,6,3,1]

# define the formatter function
# first input is the tick value, second input is the tick position
# returns the tick label string
def thousandsFormatter(x,pos):
	return '{0:.0f}K'.format(x/10000)

# create a plotting area and get the figure, axes handle in return
fig, ax = plt.subplots()

# plot data on the axes handle
ax.plot(x, y)

# set x axis major ticks format as 2 decimal places
ax.xaxis.set_major_formatter(plt.FuncFormatter(thousandsFormatter))

# print the plot
plt.show()

matplotlib_func_formatter_demo

Setting axis tick labels manually using ‘FixedFormatter’

FixedFormatter should be generally used along with FixedLocator. Otherwise the labels and ticks may not match most of the times.

import matplotlib.pyplot as plt
x = [0,1,2,3,4,5,6,7,8]
y = [8,6,4,2,9,7,6,3,1]

# create a plotting area and get the figure, axes handle in return
fig, ax = plt.subplots()

# plot data on the axes handle
ax.plot(x, y)

# set number of major x tick locations manually using FixedLocator
ax.xaxis.set_major_locator(plt.FixedLocator(x))

# set x axis ticks labels manually using FixedFormatter
labels = ['zero','one','two','three','four','five','six','seven','eight']
ax.xaxis.set_major_formatter(plt.FixedFormatter(labels))

# print the plot
plt.show()

matplotlib_linearlocator_demo

Hiding tick labels using ‘NullFormatter’

import matplotlib.pyplot as plt
x = [0,1,2,3,4,5,6,7,8]
y = [8,6,4,2,9,7,6,3,1]

# create a plotting area and get the figure, axes handle in return
fig, ax = plt.subplots()

# plot data on the axes handle
ax.plot(x, y)

# use null locator to hide major and minor ticks
ax.yaxis.set_major_formatter(plt.NullFormatter())
ax.yaxis.set_minor_formatter(plt.NullFormatter())
ax.xaxis.set_minor_formatter(plt.NullFormatter())
ax.xaxis.set_major_formatter(plt.NullFormatter())

# print the plot
plt.show()

matplotlib_null_formatter_demo

‘DateFormatter’ for formatting date labels

import datetime as dt
import matplotlib.pyplot as plt
import matplotlib.dates as mdates

# get today date
today = dt.datetime.today()
numDays = 9

x = [today-dt.timedelta(days=p) for p in range(numDays)]
y = [8,6,4,2,9,7,6,3,1]

# create a plotting area and get the figure, axes handle in return
fig, ax = plt.subplots()

# set x axis major ticks date format using funcFormatter
ax.xaxis.set_major_formatter(plt.FuncFormatter(mdates.DateFormatter('%d-%b')))

# plot data on the axes handle
ax.plot(x, y)

# print the plot
plt.show()

matplotlib_date_formatter_demo

Summary of Locators

FormatterClass Description
NullFormatter No labels on the ticks
IndexFormatter Set the strings from a list of labels
FixedFormatter Set the strings manually for the labels
FuncFormatter User-defined function sets the labels
FormatStrFormatter Use an old-style sprintf format string
StrMethodFormatter Use string format method
ScalarFormatter Default formatter for scalars: autopick the format string
LogFormatter Default formatter for log axes
PercentFormatter Format labels as a percentage

matplotlib_tick_formatters_illustration

Check out this post for all locators example code

Video

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Online Interpreter

Although we recommend to practice the above examples in Visual Studio Code, you can run these examples online at https://pynative.com/online-python-code-editor-to-execute-python-code/

References

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