title: Change stacked bar plot legend in Python
body: <p>I have the following data in a csv file:</p>
  
  <pre><code>Date    City    TruckA  TruckB  TruckC  TruckD
  Date1   City1   1   0   0   0
  Date1   City2   0   0   1   0
  Date1   City3   1   0   0   0
  Date1   City4   0   0   1   0
  Date2   City1   1   0   0   0
  Date2   City2   0   1   0   0
  Date2   City3   0   0   0   1
  Date2   City4   1   0   0   0
  Date2   City5   0   1   0   0
  Date3   City1   1   0   0   0
  Date3   City2   0   0   1   0
  Date3   City3   1   0   0   0
  Date3   City4   0   0   1   0
  </code></pre>
  
  <p>I can successfully plot the data with this code:</p>
  
  <pre><code>import pandas as pd
  
  df = pd.read_csv("data.csv")
  
  print(df)
  
  df = df.set_index(["Date","City"])
  
  df.unstack().plot(kind='bar', stacked=True)
  </code></pre>
  
  <p>I get the following result:
  <img src="https://i.imgur.com/KeQWM9X.png" alt="Image"></p>
  
  <p>As you can see, the color legend is such as each pair (City,Truck) has a color. I would like the legend to only depend on the Truck, and ideally have  labels on the bar chart for each City. </p>
  
  <p>Is this possible?</p>