How to read a column of csv as dtype list using pandas?

Question

I have a csv file with 3 columns, wherein each row of Column 3 has list of values in it. As you can see from the following table structure

Col1,Col2,Col3 1,a1,"['Proj1', 'Proj2']" 2,a2,"['Proj3', 'Proj2']" 3,a3,"['Proj4', 'Proj1']" 4,a4,"['Proj3', 'Proj4']" 5,a5,"['Proj5', 'Proj2']" 

Whenever I try to read this csv, Col3 is getting read as str object and not as list. I tried to alter the dtype of that column to list but got "Attribute Error" as below

df = pd.read_csv("inputfile.csv") df.Col3.dtype = list  AttributeError                            Traceback (most recent call last) <ipython-input-19-6f9ec76b1b30> in <module>() ----> 1 df.Col3.dtype = list  C:\Python27\lib\site-packages\pandas\core\generic.pyc in __setattr__(self,         name, value)    1953                     object.__setattr__(self, name, value)    1954             except (AttributeError, TypeError): -> 1955                 object.__setattr__(self, name, value)    1956     1957     #---------------------------------------------------------------------- 

AttributeError: can't set attribute

It would be really great if you can guide me how to go about it.

Answer 1

You could use the ast lib:

from ast import literal_eval   df.Col3 = df.Col3.apply(literal_eval) print(df.Col3[0][0]) Proj1 

You can also do it when you create the dataframe from the csv, using converters:

df = pd.read_csv("in.csv",converters={"Col3": literal_eval}) 

If you are sure the format is he same for all strings, stripping and splitting will be a lot faster:

 df = pd.read_csv("in.csv",converters={"Col3": lambda x: x.strip("[]").split(", ")}) 

But you will end up with the strings wrapped in quotes