title: Contour plots in python with time on X-Axis
body: <p>I wish to do a contour plot in python with the sample data given below:-
  X-Axis(Time)   Y-Axis(D) Z-Axis(C)
  15:18:48         10        26
  15:18:49         11        28
  15:18:50         13        30
  .                .         .
  .                .         .
  Given below is my code</p>
  <pre><code>enter code here
  import pandas as pd
  import numpy as np
  import matplotlib.pyplot as plt
  load_var=pd.read_excel(r'path\file.xlsx')
  x=pd.DataFrame(load_var['Time'])
  y=pd.DataFrame(load_var['D'])
  z=pd.DataFrame(load_var['C'])
  plt.contour(x,y,z)
  </code></pre>
  <p>Error : TypeError: unhashable type: 'numpy.ndarray'
  Kindly clear the following doubts:
  1] How to create the mesh-grid using X-axis as time and Y-axis as values mentioned under 'D' ?
  2] Please Suggest the updations in the code.</p>
  <p>Thank you.</p>