How to set value for particular cell in pandas DataFrame using index

0 votes

I've created a Pandas DataFrame

df = DataFrame(index=['A','B','C'], columns=['x','y'])

and got this

    x    y
A  NaN  NaN
B  NaN  NaN
C  NaN  NaN


Then I want to assign value to particular cell, for example for row 'C' and column 'x'. I've expected to get such result:

    x    y
A  NaN  NaN
B  NaN  NaN
C  10  NaN

with this code:

df.xs('C')['x'] = 10

but contents of df haven't changed. It's again only NaNs in DataFrame.

Any suggestions?

Jan 5 in Python by Rajiv
• 8,890 points
1,823 views

1 answer to this question.

0 votes

Why df.xs('C')['x']=10 does not work:

df.xs('C') by default, returns a new dataframe with a copy of the data, so

df.xs('C')['x']=10

modifies this new dataframe only.

df['x'] returns a view of the df dataframe, so

df['x']['C'] = 10

modifies df itself.

Warning: It is sometimes difficult to predict if an operation returns a copy or a view. For this reason the docs recommend avoiding assignments with "chained indexing".


So the recommended alternative is

df.at['C', 'x'] = 10

which does modify df.


In [18]: %timeit df.set_value('C', 'x', 10)
100000 loops, best of 3: 2.9 µs per loop

In [20]: %timeit df['x']['C'] = 10
100000 loops, best of 3: 6.31 µs per loop

In [81]: %timeit df.at['C', 'x'] = 10
100000 loops, best of 3: 9.2 µs per loop
answered Jan 5 by Gitika
• 65,950 points

Related Questions In Python

0 votes
1 answer

How to get value in Pandas dataframe using index?

You can use the iloc method to do ...READ MORE

answered Apr 8, 2019 in Python by Rohit
1,891 views
0 votes
1 answer

How to find the index of a particular value in a dataframe?

First, use the dataframe to match the ...READ MORE

answered Apr 8, 2019 in Python by Esha
141,349 views
+1 vote
3 answers

How to change/update cell value in Python Pandas dataframe?

You can use the at() method to ...READ MORE

answered Apr 8, 2019 in Python by Kunal
129,543 views
0 votes
1 answer

How to check if a value exists in pandas dataframe index?

Hello @kartik, Basically instead of raising exception I ...READ MORE

answered Jun 15, 2020 in Python by Niroj
• 82,820 points
4,290 views
0 votes
1 answer

How to rename columns in pandas (Python)?

You can use the rename function in ...READ MORE

answered Apr 30, 2018 in Data Analytics by DeepCoder786
• 1,720 points

edited Jun 8, 2020 by MD 760 views
0 votes
1 answer

What is the Difference in Size and Count in pandas (python)?

The major difference is "size" includes NaN values, ...READ MORE

answered Apr 30, 2018 in Data Analytics by DeepCoder786
• 1,720 points

edited Jun 8, 2020 by Gitika 1,579 views
0 votes
2 answers

Replacing a row in pandas data.frame

key error. I love python READ MORE

answered Feb 18, 2019 in Data Analytics by anonymous
9,678 views
0 votes
1 answer

Converting a pandas data-frame to a dictionary

Emp_dict=Employee.to_dict('records') You can directly use the 'to_dict()' function ...READ MORE

answered May 23, 2018 in Data Analytics by Bharani
• 4,620 points
3,629 views
+2 votes
4 answers

How can I replace values with 'none' in a dataframe using pandas

Actually in later versions of pandas this ...READ MORE

answered Aug 13, 2018 in Python by bug_seeker
• 15,550 points
50,959 views
0 votes
1 answer

How to combine two columns of text in pandas dataframe?

If both columns are strings, you can ...READ MORE

answered Jan 5 in Python by Gitika
• 65,950 points
607 views