在Python中比较和均衡两个数据帧

Question

I have the following dataframes: df1

C1    C2
F56   345
G45   65
H13   56
H67   578
Y78   64

df2

C1    C2
A34   10
F56   345
H13   56
Y78   64

I want to compare the above two dataframes and if df1 contains a value in C1 which is not present in df2 or vise-versa I want to add a new row with the missing value with corresponding C2 value = 0. So the resulting dataframes will look like the following.

df1

C1    C2
A34   0
F56   345
G45   65
H13   56
H67   578
Y78   64

df2

C1    C2
A34   10
F56   345
G45   0
H13   56
H67   0
Y78   64

Appreciate any recommendations.

Answer 1

This is a great use case for DataFrame.merge: https://pandas.pydata.org/pandas-docs/version/0.23/generated/pandas.DataFrame.merge.html

What is awesome about merge that the manner of the join will be familiar if you've spent any time in a relational database (left, right, inner, outer).

The indicator parameter is of particular interest to you in this case:

result_df1 = df1.merge(
    df2,
    how = "outer",
    on = "C1",
    indicator = True,
    suffixes = ("", "_df2")
)

So the results with np.nan in column C2 in this specific join you'll want to fill with 0 and then drop the extra columns we've introduced.