Access a list within a dataframe pandas

Question

I'm working on dataframes with PANDAS in Python. I read a csv file with pandas.read_csv(...). In this csv file the column 'possible_stops' contains lists (each cells in this column looks like : [ ] or [str0,str1]).

I want to iterate over the rows with itertuples() and for each row i want to access the list inside 'possible_stops' column. However, the dtype of this column is object and when i look for the type of a specific cell (type(row.possible_stops)) it returns str. I think there is something to do with dtype = .. inside the read_csv method but i don't exactly know what to do.

How can i convert cells inside this column into lists ?

Thanks very much!

EDIT : the resulting df looks like :

latitude longitude gps_speed possible_stops    
1.05869 1574942547  0.0 [['Bapeaume', 2]]
1.05862 1573910439  0.0 [['Bapeaume', 2]]
1.05862 1573910441  0.0 [['Bapeaume', 2]]
1.05862 1573910443  0.0 [['Bapeaume', 2]]
1.05862 1573910445  0.0 [['Bapeaume', 2]]
1.05862 1573910447  0.0 [['Bapeaume', 2]]

object is not strictly a dtype (see this answer). Can you supply an example of your data? I think it should be possible to access the lists inside the column — flurble
– flurble, Commented Mar 25, 2020 at 14:15

Rens · Accepted Answer · 2020-03-25 14:34:21Z

1

It is not possible for an item in a column in a Pandas dataframe to have the data type 'list'. See a list of possible datatypes for a dataframe column here: https://pbpython.com/pandas_dtypes.html.

So instead of it having the type 'list' when stored in a dataframe a list is inserted as a string object. However, it is still possible to enter the items in the lists in the dataframe with a double for-loop. For example to print each item:

import pandas as pd

data = {'possible_stops':[['str0', 'str1'], ['str2', 'str3']], 'Age':[[20, 21], [19, 18]]} 
df = pd.DataFrame(data) 
for row in df.itertuples():
    for item in row.possible_stops:
        print(item)

This will print the names in the created dataset one by one.

answered Mar 25, 2020 at 14:34

Rens

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Pi-R · Accepted Answer · 2020-03-25 14:49:43Z

0

I found a way to convert the cells into lists with ast.literal_eval()

for row in selection_traces.itertuples():
l=ast.literal_eval(row.possible_stops)

The problem has been already solved on this forum... Sorry and thanks you !

answered Mar 25, 2020 at 14:49

Pi-R

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