Error with lambda function in pandas

Question

I have a data frame sp with a column named Status. The values in the Status column are either 'Done' or 'Waiting'. I need to change the values of the Status column using a lambda function, where a status of 'Done' is changed to 'A' and a status of 'Waiting' is changed to 'N'. This is how I tried to do it:

sp['Status'] = sp['Status'].apply(lambda x: x='A' if x=='Done' else x='N')

I then get the following error message:

sp['Status'] = sp['Status'].apply(lambda x: x='A' if x=='Done' else x='N')
                                                                     ^
SyntaxError: invalid syntax

Where am I doing wrong?

Your error message doesn't match your code. Please do post the actual error so as not to confuse answerers. — Martijn Pieters
– Martijn Pieters, Commented May 15, 2016 at 12:25

Martijn Pieters · Accepted Answer · 2016-05-15 12:35:45Z

2

You can't use assignment (a statement) inside a lambda (which only takes expressions).

The lambda should instead just return the new value:

sp['Status'] = sp['Status'].apply(lambda x: 'A' if x == 'Alive' else 'N')

The result of the expression in a lambda is always the return value.

Note that you just use Series.map() here instead:

sp['Status'] = sp['Status'].map({'Alive': 'A', 'Waiting': 'N'})

edited May 15, 2016 at 12:35

answered May 15, 2016 at 12:23

Martijn Pieters

1.1m326 gold badges4.2k silver badges3.4k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Zah · Accepted Answer · 2016-05-15 12:26:18Z

1

You have to read the lambda syntax as if there was a return in front. And you cannot make assignments in the lambda body:

sp['Status'] = sp['Status'].apply(lambda x: 'A' if x=='Done' else 'N')

answered May 15, 2016 at 12:26

Zah

6,8541 gold badge26 silver badges34 bronze badges

Collectives™ on Stack Overflow

Error with lambda function in pandas

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related