python class attributes to pandas dataframe

Question

I would like to populate a pandas dataframe from attributes of a list of classes generated via 'append'. (not sure this is the right term to describe 'allFoo' below Here is a stripped down example code:

class foo(object):
def __init__(self,input):
    self.val=input
    #in real life, there will be many more attributes in this class
allFoo=[];
for i in range(10):
    allFoo.append(foo(i))

now I would like to define a new pandas data frame 'df' that gets populated from allFoo.val (and not any other attributes)

something like this:

df[0]=foo[0].val
df[1]=foo[1].val

etc

I am coming from matlab where I would try something like this: dataFrame=allFoo[:].val

how can I achieve this in python/pandas?

Sorry are you just asking how to add a new column/array of values? — EdChum
– EdChum, Commented Dec 3, 2015 at 11:53

KT. · Accepted Answer · 2017-06-09 18:04:50Z

36

For your "stripped-down" example the following code would do the job:

pd.DataFrame([f.val for f in allFoo], columns=['val'])

In a slightly more general case, where you are sure you can take all field values from your objects, the following should work just as well:

pd.DataFrame([vars(f) for f in allFoo])

In a yet more general case, when your objects may contain some fields that you need in the data frame, and other fields which you do not, there is no way around specifying this list of fields. The following code might help then:

fields = ['val', 'other_field']
pd.DataFrame([{fn: getattr(f, fn) for fn in fields} for f in allFoo])

The moral: whenever you do not know a "built-in method" for something, list comprehension is your first choice.

edited Jun 9, 2017 at 18:04

answered Dec 3, 2015 at 11:59

KT.

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4 Comments

Tony Over a year ago

Is the code above placed within the class, within the function, or outside the class?

KT. Over a year ago

Wherever you need to create the data frame from a list of objects.

Tony Over a year ago

Thank you for the response :) I tried to input a version of option 3 into my code however got a error code saying that my object is not iterable. After a little research I believe that issue should be cleared by the [] surrounding the {fn..}, no? Or am I missing something else?

KT. Over a year ago

pd.DataFrame constructor expects a list. This is how it is done in "option 3". You should not need to add any more []-s, though.

blubgz · Accepted Answer · 2023-06-18 11:03:31Z

0

Another option would be to use dict of a object

pd.DataFrame([f.__dict__ for f in allFoo])

answered Jun 18, 2023 at 11:03

blubgz

1

1 Comment

Community Over a year ago

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Plasma · Accepted Answer · 2015-12-03 12:00:31Z

-2

As EdChum suggested in a comment:

import pandas as pd
allfoo = [1, 2, 3, 4]
df = pd.DataFrame()
df["val"] = allfoo
print df

Outputs

answered Dec 3, 2015 at 12:00

Plasma

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1 Comment

jlarsch Over a year ago

for some reason, the command 'df = pd.DataFrame()' crashes my spyder python 2.7 on windows 7. So I went with KT's answer below which does what I need.

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