CODEWITHSUNDEEP
python-3.xpandasdataframe
Sean Payne
Sean Payne

Reputation: 1961

Fixing Pandas NaN when making a new column?

I have two Panda's Dataframes

id   volume
1       100
2       200
3       300

and

id   2020-07-01  2020-07-02 ...
1            12          14
2             5          1
3             7          8

I am trying to make a new column in the first table based on the values in the second table.

df['Total_Change'] = df2.iloc[:, 0] - df2.iloc[:, -1]
df['Change_MoM'] = df2.iloc[:, -2] - df2.iloc[:, -1]

This works, but the values are all shifted down in the table by one so that the first value is NaN and the last value is lost, so that my result is

id  volume  Total_Change  Change_MoM
1      100           NaN         NaN
2      200            -2          -2
3      300             4           4

Why is this happening? I've already double checked that the df2.iloc statements are grabbing the correct values, but I don't understand why my first table is shifting the values down a row. I've also tried shifting the table up one, but that left an NaN at the bottom.

The two tables are the same size. To be clear, I want to know how to prevent the NaN from occurring in the first place, not to replace it with some other value.

Upvotes: 0

Views: 43

Answers (1)

BENY
BENY

Reputation: 323236

Both dfs have different index a quick fix is add reset_index()

df=df.reset_index(drop=True)
df2=df2.reset_index(drop=True)

Upvotes: 1

Related Questions