Create a DataFrame from a dictionary of DataFrames

Question

I have a dictionary of DataFrames, where the keys are assumed to be meaningful:

In [32]: x = pd.DataFrame(dict(foo=[1,2,3], bar=[4,5,6])).set_index('foo') In [33]: y = pd.DataFrame(dict(foo=[7,8,9], bar=[10,11,12])).set_index('foo') In [34]: z = dict(x=x, y=y)

Which looks like:

In [43]: x Out[43]: bar foo 1 4 2 5 3 6 In [44]: y Out[44]: bar foo 7 10 8 11 9 12

Is there a nice way to get the following DataFrame:

 foo bar x 1 4 2 5 3 6 y 7 10 8 11 9 12

joris · Accepted Answer · 2015-07-16 16:28:12Z

7

You can use concat for this, and the keys of the dictionary will automatically be used for a new index level:

In [6]: z = dict(x=x, y=y) In [7]: pd.concat(z) Out[7]: bar foo x 1 4 2 5 3 6 y 7 10 8 11 9 12

You can also give this new index level a name using the names argument of concat (eg names=['key']).

edited Jul 16, 2015 at 16:28

answered Jul 16, 2015 at 16:23

joris

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4 Comments

LondonRob Over a year ago

Every time I discover something new about pandas I love it more and more. Bonus points for the names= part too.

user1318135 Over a year ago

The names option of this yields "ValueError: Length of names must match number of levels in MultiIndex." for me.

joris Over a year ago

pd.concat(z, names=['key']) works fine for me. What version of pandas are you using? If you still have a problem with, please open a new question.

ankush jamthikar Over a year ago

pd.concat(z, names=['key']) is a nice attempt! This post is really helpful for me.

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