How to display a dataframe while changing one of its column value?

Question

Let's take this dataframe :

df = pd.DataFrame(dict(Col1=['a','b','c'], Col2=[1,-3,2]))
  Col1  Col2
0    a     1
1    b    -3
2    c     2

I would like to display this dataframe while changing Col2, replacing negative numbers by "neg" and positive ones by "pos".
I could modify the column / add a new column then display or create a new dataframe specially to display that but I wonder if there is a more optimal way to do as I don't want to keep this modification.

I tried the following but I get the error "lambda cannot contain assignment" :

df.apply(lambda x : x['Col2'] = "pos" if x['Col2'] >= 0 else "neg")

Is there please a way to do ?

`df['Col2'] = np.where(df['Col2'] >= 0 ,'pos','neg')` you dont need apply for this actually , to just display and not modify use same with assign which returns a copy : `df.assign(Col2=np.where(df['Col2'] >= 0 ,'pos','neg'))` — anky, Mar 25 '20 at 14:47
Do not delete the question! That defeats the purpose of Stack Overflow! — Prune, Mar 25 '20 at 14:50
I had closed it as a duplicate of https://stackoverflow.com/questions/19913659/pandas-conditional-creation-of-a-series-dataframe-column , not sure why was this reopened — anky, Mar 25 '20 at 14:55
I don't see why it is duplicate of this ? There is no df.assign in this post — Ewdlam, Mar 25 '20 at 14:57
i see what you mean , i was more focussed on the code not working part of it. I will post an answer — anky, Mar 25 '20 at 15:01
I wrote one, do you want I delete it in order to you wrote yours ? — Ewdlam, Mar 25 '20 at 15:02

Ewdlam · Accepted Answer · 2020-03-25T16:05:39.027

1

In agreement with @anky_91 comment, the solution is using df.assign :

df.assign(Col2=np.where(df['Col2'] >= 0 ,'pos','neg'))

Output :

  Col1 Col2
0    a  pos
1    b  neg
2    c  pos

edited Mar 25 '20 at 16:05

answered Mar 25 '20 at 15:01

Ewdlam

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How to display a dataframe while changing one of its column value?

1 Answers1