Most pythonic way to search for values in one column whom value in an other is above a treshold-CodePudding

I have a pandas DataFrame df as follow :

siren ratio
1      20
2      25
1      40
3      16
3      19
4      35

My goal is to have a df2 with only siren whom ratio value is above 30 at least one time as follow :

siren ratio
1      20
1      40
4      35

Today, I do it in two steps :

First, I use a filter to get all the uniques siren with a value above 30 :

value_30 = df[df["ratio"] > 30]["siren"].unique()

Then, I use value_30 as a list in order to filter my df, and to get my df2.

However, I'm not satisfied with this solution and I think there are a most pythonic way to do this. Any idea ?

CodePudding user response：

Try with groupby and transform:

value_30 = df[df.groupby("siren")["ratio"].transform("max")>30]

>>> value_30
   siren  ratio
0      1     20
2      1     40
5      4     35

CodePudding user response：

res = df.groupby(df.siren).filter(lambda x: x["ratio"].max() > 30)
print(res)

Output

   siren  ratio
0      1     20
2      1     40
5      4     35

CodePudding user response：

df[df['ratio'].gt(30).groupby(df['siren']).transform('max')]

    siren  ratio
0      1     20
2      1     40
5      4     35