Pandas.groupby().ngroup()分组后如何通过ID取回组名

Question

I have grouped my data in pandas by ID

df['cityID']=df.groupby(['city']).ngroup()

df =
    names    city       cityID
    ali     Islamabad      0
    john    lahore         1
    aslam   Islamabad      0
    khan    Peshawar       2
    umair   lahore         1

df2 =

    cityID    city
      2        ?
      1        ?
      2        ?
      2        ?
      0        ?
      1        ?
      1        ?
      2        ?
      1        ?
      0        ?
      2        ?
      0        ?

after come calculations I got cityIDs I want to convert them back to city names in pandas using python. populating using the cityIDs

Answer 1

If I understood correct, you want to retrieve a column value based on other column:

print(df.loc[df['cityID'] == 1, 'city'].iloc[0])

But if what you want is to assign a value to a column depending on a dictionary:

d = {0: 'Islamabad', 1: 'lahore', 2: 'Peshawar'}
df["New_col"] = df["cityID"].apply(lambda x: d.get(x))