Python/Pandas - Combine two columns with NaN values

Question

Lets say i have a dataframe with two columns: OldValue and NewValue

i want to do some plotting and i want to combine values. If OldValue is empty, NewValue is filled, and the other way around. There is not a single instance both or neither are filled. Lets say my dataframe looks like this:

  OldValue NewValue
0  14.0     NaN 
1  NaN     7.0
2  3.0     NaN
3  NaN     3.0

I found that i could fillna(0) and then do something along the lines of

df["AllValue"] = df["NewValue"] + df["OldValue"]

Is this the most efficient way?

Check this: stackoverflow.com/a/72164923/7066658

Ali
– Ali

2022-05-10 10:31:11 +00:00
Commented May 10, 2022 at 10:31 — Ali
– Ali, Commented May 10, 2022 at 10:31

jezrael · Accepted Answer · 2022-05-10 10:37:35Z

4

Your solution should be change with Series.add and fill_value=0:

df["AllValues"] = df["Newvalues"].add(df["OldValues"], fill_value=0)

Or use Series.fillna:

df["AllValue"] = df["NewValue"].fillna(df["OldValue"])

edited May 10, 2022 at 10:37

answered May 10, 2022 at 10:26

jezrael

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Comments

Bill · Accepted Answer · 2022-05-10 10:29:42Z

1

I think this will work:

df["AllValue"] = df["OldValue"]  # make a copy
df.loc[df["AllValue"].isna(), "AllValue"] = df.loc[~df["NewValue"].isna(), "NewValue"]

answered May 10, 2022 at 10:29

Bill

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