title: Bars in matplotlib bar chart are not the same width?
body: <p>I was trying to use matplotlib and pandas to create a bar chart that shows the daily change in COVID-19 cases for the USA.</p>
  <pre><code>  import pandas as pd
    import matplotlib.pyplot as plt
  
    data = pd.read_csv('https://raw.githubusercontent.com/nytimes/covid-19-data/master/us-counties.csv')
    display(data.head(10))
    df = data.groupby('date').sum()
    df['index'] = range(len(df))
    df['IsChanged'] = df['cases'].diff() 
  
  
    df.at['2020-01-21', 'IsChanged'] = 0.0
  
    x = df['index']
    z = df['IsChanged']
  
    plt.figure(figsize=(20,10))
    plt.grid(linestyle='--')
    plt.bar(x,z)
    plt.show()
  </code></pre>
  <p>The graph that I get though, looks like this:<br />
  <img src="https://i.stack.imgur.com/HWwpG.png" alt="" />.</p>
  <p>The width of the bars of the chart are not even. I tried setting a specific width, but that didn't work. Is there a way to fix this?</p>