Plotting two pandas dataframe columns against each other in multiindex

Question

Let's say, we have a pandas DataFrame:

df = pd.DataFrame(np.array([[1,2,3,4,5],[3,4,5,6,7]]).T, columns=['a','b'])

print(df)

which gives me:

if I try to plot column 'a' on column 'b', I can very simply do:

df.plot(x='a', y='b')
plt.show()

and so I do get my graph.

But if I have a DataFrame with a MultiIndex on the Columns, then I have a problem:

df = pd.DataFrame(np.array([[1,2,3,4,5],[3,4,5,6,7]]).T, columns=[['a','b'],['y','w']])

print(df)

which gives me:

so if I do now:

df.plot(x=['a','y'], y=['b','w'])
plt.show()

I get the following error:

File "pandas/_libs/index.pyx", line 117, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/index.pyx", line 139, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/hashtable_class_helper.pxi", line 1265, in pandas._libs.hashtable.PyObjectHashTable.get_item
File "pandas/_libs/hashtable_class_helper.pxi", line 1273, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 'y'

Am I doing anything wrong?

Or is pandas not able to plot when using a MultiIndex?

You can. You just need to set the index before plotting. Try df.set_index(('a', 'y')).plot(). — cs95
– cs95, Commented Dec 13, 2017 at 13:28
Thanks, this work, but is just a workaround. I expect the function plot(x=['a','y'], y=['b','w']) to work both with single and with multiple column index. — DavideC
– DavideC, Commented Dec 13, 2017 at 13:41
No, I see it won't, but I think then pandas should work on it for code coherency. — DavideC
– DavideC, Commented Dec 13, 2017 at 13:43

MaxU - stand with Ukraine · Accepted Answer · 2017-12-13 13:29:13Z

1

Try this:

df.set_index(('a','y')).plot()

Result:

edited Dec 13, 2017 at 13:29

answered Dec 13, 2017 at 13:27

MaxU - stand with Ukraine

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5 Comments

cs95 Over a year ago

Aha, didn't see your answer when I posted my comment.

MaxU - stand with Ukraine Over a year ago

@cᴏʟᴅsᴘᴇᴇᴅ, thank you! Congratulations! You are [legendary] now! ;-)

cs95 Over a year ago

Thank you so much! Couldn't have done it without you guys :-)

BENY Over a year ago

@cᴏʟᴅsᴘᴇᴇᴅ Congratulations !! lengendary achieved

cs95 Over a year ago

@Wen Thanks, couldn't have done it without you guys' help!

Mike · Accepted Answer · 2020-06-06 18:04:00Z

0

I think this is a more straight forward way to do it:

df.plot(x=('a','y'), y=('b','w'))

answered Jun 6, 2020 at 18:04

Mike

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