python - Applying a custom function on Group By if row count greater than 1 -

how apply function dataframe after grouping if want apply function on groups group has membership greater 1.

e.g

 df1 = df.groupyby(['x','y']).count() > 1.apply(f)   f(x) :    

secondly being passed function - elements on group or group itself.

i think need size:

df1 = df.groupby(['x','y']).size()  df1[df1 > 1] =  df1[df1 > 1].apply(f) 

aggregating size , count - differences.

sample:

df = pd.dataframe({'x':[1,1,3],                    'y':[5,5,6],                    'c':[7,8,9]})  print (df)    c  x  y 0  7  1  5 1  8  1  5 2  9  3  6  def f(x) :    return x + 2 

---

df1 = df.groupby(['x','y']).size()  s = df1[df1.count > 1].set_index('x')['y'] print (s) x 1    5 name: y, dtype: int64  mask = df.set_index('x')['y'].isin(s).values print (mask) [ true  true false]  df[mask] = df[mask].apply(f) print (df)     c  x  y 0   9  3  7 1  10  3  7 2   9  3  6