根据另一个数据帧的多个列过滤数据帧

Question

I have a dataframe like this:

    ID1    ID2
0   foo    bar
1   fizz   buzz

And another like this:

    ID1    ID2    Count    Code   
0   abc    def      1        A
1   fizz   buzz     5        A
2   fizz1  buzz2    3        C
3   foo    bar      6        Z
4   foo    bar      6        Z

What I would like to do is filter the second dataframe where ID1 and ID2 match a row in the first dataframe, and whenever there's a match I want to remove that row from the first dataframe to avoid duplicates. This would yield a dataframe that looks like this:

    ID1    ID2    Count    Code   
1   fizz   buzz     5        A
3   foo    bar      6        Z

I know I can do this by nesting for loops, stepping through all the rows, and manually removing a row from the first frame whenever I get a match but I am wondering if there is a more pythonic way to do this. I am not experienced in pandas so there may be a much cleaner way to do that I do not know about. I was previously using .isin() but had to scrap it. Each ID pair can exist in the dataframe up to N times and I need the filtered frame to contain between 0 and N instances of a pair.

Answer 1

Use merge with drop_duplicates , if only same columns for join in both df :

df = pd.merge(df1,df2.drop_duplicates())
print (df)
    ID1   ID2  Count Code
0   foo   bar      6    Z
1  fizz  buzz      5    A

If need check dupes only in ID columns:

df = pd.merge(df1,df2.drop_duplicates(subset=['ID1','ID2']))
print (df)
    ID1   ID2  Count Code
0   foo   bar      6    Z
1  fizz  buzz      5    A

If more columns are overlaping add parameter on :

df = pd.merge(df1, df2.drop_duplicates(), on=['ID1','ID2'])

---

If not remove dupe rows:

df = pd.merge(df1,df2)
print (df)
    ID1   ID2  Count Code
0   foo   bar      6    Z
1   foo   bar      6    Z
2  fizz  buzz      5    A

Answer 2

尝试这个：

df2.merge(df1[['ID1','ID2']])

Answer 3

Or maybe try this ?

df.loc[(df.ID1.isin(df1.ID1))&(df.ID2.isin(df1.ID2)),:].drop_duplicates()


Out[224]: 
    ID1   ID2  Count Code
1  fizz  buzz      5    A
3   foo   bar      6    Z

Answer 4

Using isin on a list of tuples

df2[
    pd.Series(
        list(zip(df2.ID1.values, df2.ID2.values))
    ).isin(list(zip(df1.ID1.values, df1.ID2.values)))
]

    ID1   ID2  Count Code
1  fizz  buzz      5    A
3   foo   bar      6    Z
4   foo   bar      6    Z

Answer 5

Merge was almost what I wanted, but didn't quite do the job because I have an odd set of requirements where I need to filter out some duplicates but not all the duplicates. A regular merge doesn't work because that keeps all the duplicates and drop_duplicates() doesn't work because I need to allow some duplicates. I ended up going with the method I described in the question and nested for loops.

temp_frame = pd.DataFrame(columns.df2.columns)
for i in xrange(len(df2)):
    for ii in xrange(len(df1)):
        if df2['ID1'].iloc[i] == df1['ID1'].iloc[ii] and df2['ID2'].iloc[i] == df1['ID2'].iloc[ii]:
            df1.drop(df1.index[ii], inplace=True)
            temp_frame = temp_frame.append(df2.iloc[i], ignore_index=True)
            break
df1 = temp_frame.copy()