Appending a list or series to a pandas DataFrame as a row?

Question

So I have initialized an empty pandas DataFrame and I would like to iteratively append lists (or Series) as rows in this DataFrame. What is the best way of doing this?

Better answers can be found under: http://stackoverflow.com/questions/10715965/add-one-row-in-a-pandas-dataframe — Yuval Atzmon, Mar 10 '17 at 20:09

score 184 · Answer 1 · answered Jan 25 '18 at 09:59

184

df = pd.DataFrame(columns=list("ABC"))
df.loc[len(df)] = [1,2,3]

answered Jan 25 '18 at 09:59

Ashot Matevosyan

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This is the easiest if you are looking to add to the end of the `df`. – Sid Jun 15 '18 at 10:42
3

This is exactly what I wanted, so simple yet effective! – MSalty Jun 16 '18 at 07:44
5

Why is this not the selected answer? – Lucas Azevedo Feb 15 '19 at 14:29
6

This is generally ok but only works if you have a monotonically increasing index that started at 0. – dreab Jul 05 '19 at 09:26

Mike Chirico · Accepted Answer · 2019-04-18T09:51:13.683

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Sometimes it's easier to do all the appending outside of pandas, then, just create the DataFrame in one shot.

>>> import pandas as pd
>>> simple_list=[['a','b']]
>>> simple_list.append(['e','f'])
>>> df=pd.DataFrame(simple_list,columns=['col1','col2'])
   col1 col2
0    a    b
1    e    f

edited Apr 18 '19 at 09:51

answered Feb 19 '16 at 15:40

Mike Chirico

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The question seems to imply that not all the rows are known up front. – DISC-O May 08 '20 at 01:54
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This doesn't answer OP's question. – Haddock-san Jan 26 '21 at 13:14

score 71 · Answer 3 · answered Oct 11 '14 at 04:37

71

Here's a simple and dumb solution:

>>> import pandas as pd
>>> df = pd.DataFrame()
>>> df = df.append({'foo':1, 'bar':2}, ignore_index=True)

answered Oct 11 '14 at 04:37

Jaidev Deshpande

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Note that this is appending a dict, not a list – anthnyprschka Nov 13 '17 at 15:39
Also note that pandas is going to remove df.append in near future. One should use pd.concat. I have written an answer with this suggestion – newbie101 Jun 16 '23 at 17:44

score 41 · Answer 4 · answered Oct 11 '14 at 02:01

41

Could you do something like this?

>>> import pandas as pd
>>> df = pd.DataFrame(columns=['col1', 'col2'])
>>> df = df.append(pd.Series(['a', 'b'], index=['col1','col2']), ignore_index=True)
>>> df = df.append(pd.Series(['d', 'e'], index=['col1','col2']), ignore_index=True) 
>>> df
  col1 col2
0    a    b
1    d    e

Does anyone have a more elegant solution?

answered Oct 11 '14 at 02:01

Alex Woolford

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Here's a simpler and dumb solution: ``` import pandas as pd df = pd.DataFrame() df = df.append({'foo':1, 'bar':2}, ignore_index=True) # Note that this appending doesn't happen in place. ``` – Jaidev Deshpande Oct 11 '14 at 04:32
The `index` parameter should probably be named `columns`; `ignore_index` here ignores the index - the name of the Series. – flow2k Nov 30 '20 at 06:42

score 33 · Answer 5 · answered Jun 19 '16 at 16:55

33

Following onto Mike Chirico's answer... if you want to append a list after the dataframe is already populated...

>>> list = [['f','g']]
>>> df = df.append(pd.DataFrame(list, columns=['col1','col2']),ignore_index=True)
>>> df
  col1 col2
0    a    b
1    d    e
2    f    g

answered Jun 19 '16 at 16:55

Jay Marm

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Does it create a copy? Is it possible to append in-place? – lucid_dreamer Aug 20 '18 at 13:03
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@lucid_dreamer This creates a copy. – flow2k Nov 30 '20 at 06:43
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The `ignore_index` parameter is optional (`False` by default). – flow2k Nov 30 '20 at 06:43

score 21 · Answer 6 · answered Dec 31 '20 at 12:40

There are several ways to append a list to a Pandas Dataframe in Python. Let's consider the following dataframe and list:

import pandas as pd
# Dataframe
df = pd.DataFrame([[1, 2], [3, 4]], columns = ["col1", "col2"])
# List to append
list = [5, 6]

Option 1: append the list at the end of the dataframe with pandas.DataFrame.loc.

df.loc[len(df)] = list

Option 2: convert the list to dataframe and append with pandas.DataFrame.append().

df = df.append(pd.DataFrame([list], columns=df.columns), ignore_index=True)

Option 3: convert the list to series and append with pandas.DataFrame.append().

df = df.append(pd.Series(list, index = df.columns), ignore_index=True)

Each of the above options should output something like:

>>> print (df)
   col1  col2
0     1     2
1     3     4
2     5     6

Reference : How to append a list as a row to a Pandas DataFrame in Python?

@DaniloMatrangoloMarano check this question : https://stackoverflow.com/questions/31593201/how-are-iloc-and-loc-different — Fifi, May 22 '21 at 14:41

score 8 · Answer 7 · answered Nov 14 '19 at 21:37

8

Converting the list to a data frame within the append function works, also when applied in a loop

import pandas as pd
mylist = [1,2,3]
df = pd.DataFrame()
df = df.append(pd.DataFrame(data[mylist]))

answered Nov 14 '19 at 21:37

janfelix

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What is `data[mylist]` ? Obviously, it throws the error `NameError: name 'data' is not defined`. Five votes show they know? – jaromrax Dec 21 '20 at 12:57
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correct should be `df = df.append(pd.DataFrame(data=[mylist]))` . It is missing '=' after data. – Jakub Mar 18 '21 at 19:46

score 5 · Answer 8 · answered Aug 04 '18 at 22:05

Here's a function that, given an already created dataframe, will append a list as a new row. This should probably have error catchers thrown in, but if you know exactly what you're adding then it shouldn't be an issue.

import pandas as pd
import numpy as np

def addRow(df,ls):
    """
    Given a dataframe and a list, append the list as a new row to the dataframe.

    :param df: <DataFrame> The original dataframe
    :param ls: <list> The new row to be added
    :return: <DataFrame> The dataframe with the newly appended row
    """

    numEl = len(ls)

    newRow = pd.DataFrame(np.array(ls).reshape(1,numEl), columns = list(df.columns))

    df = df.append(newRow, ignore_index=True)

    return df

bmello · Answer 9 · 2016-09-03T02:51:57.063

If you want to add a Series and use the Series' index as columns of the DataFrame, you only need to append the Series between brackets:

In [1]: import pandas as pd

In [2]: df = pd.DataFrame()

In [3]: row=pd.Series([1,2,3],["A","B","C"])

In [4]: row
Out[4]: 
A    1
B    2
C    3
dtype: int64

In [5]: df.append([row],ignore_index=True)
Out[5]: 
   A  B  C
0  1  2  3

[1 rows x 3 columns]

Whitout the ignore_index=True you don't get proper index.

score 3 · Answer 10 · answered Aug 30 '18 at 03:23

3

simply use loc:

>>> df
     A  B  C
one  1  2  3
>>> df.loc["two"] = [4,5,6]
>>> df
     A  B  C
one  1  2  3
two  4  5  6

answered Aug 30 '18 at 03:23

Qinsi

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score 3 · Answer 11 · edited Jan 09 '21 at 13:21

3

Consider an array A of N x 2 dimensions. To add one more row, use the following.

A.loc[A.shape[0]] = [3,4]

edited Jan 09 '21 at 13:21

Tomer Shetah

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answered Jan 09 '21 at 12:57

Samiran Bera

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you can create code block for code with 3 backticks – Chandan Jan 09 '21 at 13:22

score 2 · Answer 12 · answered Jun 20 '20 at 18:54

As mentioned here - https://kite.com/python/answers/how-to-append-a-list-as-a-row-to-a-pandas-dataframe-in-python, you'll need to first convert the list to a series then append the series to dataframe.

df = pd.DataFrame([[1, 2], [3, 4]], columns = ["a", "b"])
to_append = [5, 6]
a_series = pd.Series(to_append, index = df.columns)
df = df.append(a_series, ignore_index=True)

Minions · Answer 13 · 2018-12-14T18:48:20.927

0

The simplest way:

my_list = [1,2,3,4,5]
df['new_column'] = pd.Series(my_list).values

Edit:

Don't forget that the length of the new list should be the same of the corresponding Dataframe.

edited Dec 14 '18 at 18:48

answered Sep 06 '18 at 08:27

Minions

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this works for a single instance of the list, but if you have multiple occurrences than my version works – Golden Lion Nov 14 '20 at 19:59

score 0 · Answer 14 · answered Jun 16 '23 at 17:54

I will give an example with pd.concat as df.append is going to get deprecated,
Let's see how to append a list to an empty dataframe(just with column headers)

Create an empty dataframe onto which we will append the list

import pandas as pd  
columns=["Col1","Col2"]  
empty_df = pd.DataFrame(columns=columns)

Append a list

list_to_append = [1,2]
dict_from_list= {k:v for k,v in zip(columns,list_to_append)}
df_for_list = pd.DataFrame(dict_from_list,index=[0])
concatenated_df = pd.concat([empty_df,df_for_list],ignore_index=True)

Appending a list or series to a pandas DataFrame as a row?

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