title: The matplotlib ticker FuncFormatter
body: <p>I am trying to manually set the ticker for a bar plot. I am using the FunFormatter function. Yet, I found that the behavior of the FunFormmater is too strange. For X-axis range from 0 to 91, I found that the FunFormmater returns the following ... Any idea how does it work.
  Here is the <a href="https://app.box.com/s/j6d7vosgkrgoxfjro49qlgpng9ug97ln" rel="nofollow noreferrer">link for the data file</a>
  Thanks in advance</p>
  
  <p>-10.0
  0.0
  10.0
  20.0
  30.0
  40.0
  50.0
  60.0
  70.0
  80.0
  90.0
  100.0
  28.805725806451605
  38.374395161290316
  41.22463709677419
  47.128709677419344
  48.55383064516128
  49.36818548387095
  51.20048387096774
  52.42201612903225
  53.439959677419345
  53.439959677419345
  53.03278225806451
  53.643548387096764
  56.08661290322579
  59.75120967741935
  64.63733870967741
  70.54141129032257
  76.85266129032257
  83.16391129032257
  95.58282258064514</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  import pandas as p
  import matplotlib.mlab as m
  import matplotlib
  import matplotlib.ticker as ticker
  
  file1=np.load('numofdays.npz')
  fig,axes=plt.subplots(ncols=1)
  ax=axes
  x=np.arange(len(file1['arr_0']))
  y=np.array(file1['arr_0'])
  ax.bar(x,y)
  mydates=p.DatetimeIndex(file1['arr_1'])
  
  def mme(xx,pos=None):
      print(xx)
  #    print(mydates[int(xx-9)].strftime('%Y-%m-%d'))
      return mydates[int(xx-9)].strftime('%Y-%m-%d')
  
  ax.xaxis.set_major_locator(ticker.MultipleLocator(10))
  ax.xaxis.set_major_formatter(ticker.FuncFormatter(mme))
  fig.autofmt_xdate()
  </code></pre>