Append values from dataframe column to list

Question

I have a dataframe with several columns, and I want to append to an empty list the values of one column, so that the desired output would be the following:

empty_list = [value_1,value_2,value_3...]

I have tried the following:

df = pd.DataFrame({'country':['a','b','c','d'],
      'gdp':[1,2,3,4],
      'iso':['x','y','z','w']})
a_list = []

a_list.append(df['iso'])
a_list.append(df['iso'].values)
a_list.append(df['iso'].tolist())

Either way, I get a list with lists, numpy arrays or series inside it, and I would like to have directly the records.

if you append to a list, you get a list within a list. so, instead of appending, just get your list directly, problem solved. — Paritosh Singh, May 27 '19 at 07:50

score 22 · Accepted Answer · edited Feb 19 '20 at 07:19

You could try this script if you need to append one column only:

a_list = df['iso'].tolist()

For extending a list by appending elements from the iterable, use extend:

a_list = []
a_list.extend(df['iso'].tolist())
a_list.extend(df['country'].tolist())
print (a_list)
['x', 'y', 'z', 'w', 'a', 'b', 'c', 'd']

Another solution is to use numpy.ravel with transpose:

a_list = df[['iso','country']].values.T.ravel().tolist()
print (a_list)
['x', 'y', 'z', 'w', 'a', 'b', 'c', 'd']

score 3 · Answer 2 · answered May 27 '19 at 07:59

extend does what you ask for . If you try do this with append, you can do something like:

import itertools
a_list = []
a_list.append(df.iso.tolist())
a_list.append(df.country.tolist())
a_list=list(itertools.chain.from_iterable(a_list))
print(a_list)

Output

['x', 'y', 'z', 'w', 'a', 'b', 'c', 'd']

score 2 · Answer 3 · answered May 27 '19 at 07:52

2

Your problem arises from the fact that df['iso'].tolist() creates a list. The list is appended (given a place in the list at the single index), so you get a list of list. You can try:

a_list.extend(df['iso'].tolist())

answered May 27 '19 at 07:52

balkon16

1,338
4
20
40

Santosh · Answer 4 · 2019-05-27T09:29:18.357

To access the data of each row of the Pandas dataframe we can use DataFrame.iat attribute and then we can append the data of each row to the end of the list. In first for loop iterate over each row and create a list to store the data of the current row In second for loop iterate over all the columns and append the data of each column to the list after that append the current row to the list

df = pd.DataFrame({'country':['a','b','c','d'],'gdp':[1,2,3,4],'iso':['x','y','z','w']})
a_list = []
for i in range((df.shape[0])):
cur_row =[]
for j in range(df.shape[1]):
    cur_row.append(df.iat[i, j])            
a_list.append(cur_row)

Please edit your answer and add the explanation to fullfill stackoverflows guidelines for good answers — Flo, May 27 '19 at 09:27

score 0 · Answer 5 · edited May 27 '19 at 10:04

0

This example should be enough:

myList = df['iso'].tolist() 
print(myList)

Output:

['x', 'y', 'z', 'w']

edited May 27 '19 at 10:04

tuomastik

4,559
5
36
48

answered May 27 '19 at 07:49

SimbaPK

566
1
7
26

I need to append the results several times through a loop, so that won't work. Sorry for not specifying it in my question – Javier Lopez Tomas May 27 '19 at 07:55

Append values from dataframe column to list

5 Answers5