Pandas Dataframe Not Displaying Column Elements

Question

I merged two dataframes but the resulting dataframe is giving back an empty column. How can this be resolved?

print(resampled_fd)

                   Time  power(dB)
0   2021-12-11 10:00:00     46.612
1   2021-12-11 10:02:00     46.902
2   2021-12-11 10:04:00     46.362
3   2021-12-11 10:06:00     47.902

print(df)

                   Time Z(dB)
0   1900-01-01 10:02:00 NaN
1   1900-01-01 10:04:00 NaN
2   1900-01-01 10:06:00 NaN
3   1900-01-01 10:08:00 NaN

dfc=pd.merge(df, resampled_fd)
pd.set_option('display.max_rows', None)
pd.set_option('display.max_columns', None)
print(dfc)```

Empty DataFrame
Columns: [Time, Z(dB), power(dB)]
Index: []

The two dataframes have zero overlap in Time. What did you expect? — Marat, Jun 29 '23 at 18:31

michaelt · Answer 1 · 2023-06-29T18:58:08.490

You could outer merge in all the data:

dfc=pd.merge(df, resampled_fd, on=['time'], how='outer')

Here's an example: https://colab.research.google.com/drive/1wumaVU5w9acKcDyhp45NtEWMt_yuz9SG?usp=sharing

The resulting df is:

time    power(db)   Z(db)
0   2021-12-11 10:00:00 46.612  NaN
1   2021-12-11 10:02:00 46.902  NaN
2   2021-12-11 10:04:00 46.362  NaN
3   2021-12-11 10:06:00 47.902  NaN
4   1900-01-01 10:02:00 NaN NaN
5   1900-01-01 10:04:00 NaN NaN
6   1900-01-01 10:06:00 NaN NaN
7   1900-01-01 10:08:00 NaN NaN

A good solution for merging has already been discussed at Pandas - merge dataframe to keep all values on left and 'insert' values from right if 'no key on left' else 'update' existing 'key' in left

score 0 · Answer 2 · answered Jun 29 '23 at 21:23

Did you mean concatenate instead of merge? If so, you can do:

df1 = pd.DataFrame({'Time': list('abc'), 'power': list('def')})
df2 = pd.DataFrame({'Time': list('ghi'), 'Z': list('jkl')})
pd.concat([df1, df2.rename(columns={'Z': 'power'})], ignore_index=True)

Output:

Time    power
0   a   d
1   b   e
2   c   f
3   g   j
4   h   k
5   i   l

Pandas Dataframe Not Displaying Column Elements

2 Answers2