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Matplotlib.ticker.IndexFormatter class in Python
  • Last Updated : 27 Apr, 2020

Matplotlib is an amazing visualization library in Python for 2D plots of arrays. Matplotlib is a multi-platform data visualization library built on NumPy arrays and designed to work with the broader SciPy stack.

matplotlib.ticker.IndexFormatter

The matplotlib.ticker.IndexFormatter class is a subclass of matplotlib.ticker class and is used to format the position x that is the nearest i-th label where i = int(x + 0.5). The positions with i len(list) have 0 tick labels.

Syntax: class matplotlib.ticker.IndexFormatter(labels)

Parameter :

  • labels: It is a list of labels.

Example 1:



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import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl
  
   
# create dummy data    
x = ['str{}'.format(k) for k in range(20)]
y = np.random.rand(len(x))
   
# create an IndexFormatter 
# with labels x
x_fmt = mpl.ticker.IndexFormatter(x)
   
fig,ax = plt.subplots()
  
ax.plot(y)
  
# set our IndexFormatter to be
# responsible for major ticks
ax.xaxis.set_major_formatter(x_fmt)

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Output:

Example 2:

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from matplotlib.ticker import IndexFormatter, IndexLocator
import pandas as pd
import matplotlib.pyplot as plt
  
  
years = range(2015, 2018)
fields = range(4)
days = range(4)
bands = ['R', 'G', 'B']
  
index = pd.MultiIndex.from_product(
    [years, fields], names =['year', 'field'])
  
columns = pd.MultiIndex.from_product(
    [days, bands], names =['day', 'band'])
  
df = pd.DataFrame(0, index = index, columns = columns)
  
df.loc[(2015, ), (0, )] = 1
df.loc[(2016, ), (1, )] = 1
df.loc[(2017, ), (2, )] = 1
ax = plt.gca()
plt.spy(df)
  
xbase = len(bands)
xoffset = xbase / 2
xlabels = df.columns.get_level_values('day')
  
ax.xaxis.set_major_locator(IndexLocator(base = xbase,
                                        offset = xoffset))
  
ax.xaxis.set_major_formatter(IndexFormatter(xlabels))
  
plt.xlabel('Day')
ax.xaxis.tick_bottom()
  
ybase = len(fields)
yoffset = ybase / 2
ylabels = df.index.get_level_values('year')
  
ax.yaxis.set_major_locator(IndexLocator(base = ybase, 
                                        offset = yoffset))
  
ax.yaxis.set_major_formatter(IndexFormatter(ylabels))
  
plt.ylabel('Year')
  
plt.show()

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Output:

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