python - Plot bar graph from Pandas DataFrame

Question

Assuming i have a DataFrame that looks like this:

Hour | V1 | V2 | A1 | A2
 0   | 15 | 13 | 25 | 37  
 1   | 26 | 52 | 21 | 45 
 2   | 18 | 45 | 45 | 25 
 3   | 65 | 38 | 98 | 14

Im trying to create a bar plot to compare columns V1 and V2 by the Hour. When I do:

import matplotlib.pyplot as plt
ax = df.plot(kind='bar', title ="V comp",figsize=(15,10),legend=True, fontsize=12)
ax.set_xlabel("Hour",fontsize=12)
ax.set_ylabel("V",fontsize=12)

I get a plot and a legend with all the columns' values and names. How can I modify my code so the plot and legend only displays the columns V1 and V2

Would it not deliver what you want by just sub-selecting the columns of interest first: ax = df[['V1','V2']].plot(kind='bar', title ="V comp",figsize=(15,10),legend=True, fontsize=12)? — EdChum
@EdChum I was trying along those line but i kept getting error messages. I'm using pandas.pydata.org/pandas-docs/version/0.15.2/visualization.html as reference and could not find an example of what i needed. But you are correct. If you answer it i can accept it. If you can add the explanation of the [ [ ] ] syntax since i was doing ax = df['V1','V2'] — Alfonso

EdChum EdChum · Accepted Answer · 2015-04-07T18:56:00

To plot just a selection of your columns you can select the columns of interest by passing a list to the subscript operator:

ax = df[['V1','V2']].plot(kind='bar', title ="V comp", figsize=(15, 10), legend=True, fontsize=12)

What you tried was df['V1','V2'] this will raise a KeyError as correctly no column exists with that label, although it looks funny at first you have to consider that your are passing a list hence the double square brackets [[]].

import matplotlib.pyplot as plt
ax = df[['V1','V2']].plot(kind='bar', title ="V comp", figsize=(15, 10), legend=True, fontsize=12)
ax.set_xlabel("Hour", fontsize=12)
ax.set_ylabel("V", fontsize=12)
plt.show()

enter image description here

python - Plot bar graph from Pandas DataFrame

1 Answers