Sorting Pandas data frame with groupby and conditions - pandas

Question

I'm trying to sort a data frame based on groups meeting conditions.
The I'm getting a syntax error for the way I'm sorting the groups.
And I'm losing the initial order of the data frame before attempting the above.
This is the order of sorting that I'm trying to achieve:
1) Sort on First and Test columns.
2) Test==1 groups, sort on Secondary then by Final column.
---Test==0 groups, sort on Final column only.
import pandas as pd
df=pd.DataFrame({"First":[100,100,100,100,100,100,200,200,200,200,200],"Test":[1,1,1,0,0,0,0,1,1,1,0],"Secondary":[.1,.1,.1,.2,.2,.3,.3,.3,.3,.4,.4],"Final":[1.1,2.2,3.3,4.4,5.5,6.6,7.7,8.8,9.9,10.10,11.11]})
def sorter(x):
if x["Test"]==1:
x.sort_values(['Secondary','Final'], inplace=True)
else:
x=x.sort_values('Final', inplace=True)
df=df.sort_values(["First","Test"],ascending=[False, False]).reset_index(drop=True)
df.groupby(['First','Test']).apply(lambda x: sorter(x))
df
Expected result:
First Test Secondary Final
200 1 0.4 10.1
200 1 0.3* 9.9*
200 1 0.3* 8.8*
200 0 0.4 11.11*
200 0 0.3 7.7*
100 1 0.5 2.2
100 1 0.1* 3.3*
100 1 0.1* 1.1*
100 0 0.3 6.6*
100 0 0.2 5.5*
100 0 0.2 4.4*

Answer 1

You can try of sorting in descending order without groupby,
w.r.t sequence you gave, the order of sorting will change.will it work for you
df=pd.DataFrame({"First":[100,100,100,100,100,100,200,200,200,200,200],"Test":[1,1,1,0,0,0,0,1,1,1,0],"Secondary":[.1,.5,.1,.9,.4,.1,.3,.3,.3,.4,.4],"Final":[1.1,2.2,3.3,4.4,5.5,6.6,7.7,8.8,9.9,10.10,11.11]})
df = df.groupby(['First','Test']).apply(lambda x: x.sort_values(['First','Test','Secondary','Final'],ascending=False) if x.iloc[0]['Test']==1 else x.sort_values(['First','Test','Final'],ascending=False)).reset_index(drop=True)
df.sort_values(['First','Test'],ascending=[True,False])
Out:
Final First Secondary Test
3 2.20 100 0.5 1
4 3.30 100 0.1 1
5 1.10 100 0.1 1
0 6.60 100 0.1 0
1 5.50 100 0.4 0
2 4.40 100 0.9 0
8 10.10 200 0.4 1
9 9.90 200 0.3 1
10 8.80 200 0.3 1
6 11.11 200 0.4 0
7 7.70 200 0.3 0

Answer 2

The trick was to sort subsets separately and replace the values in the original df.
This came up in other solutions to pandas sorting problems.
import pandas as pd
df=pd.DataFrame({"First":[100,100,100,100,100,100,200,200,200,200,200],"Test":[1,1,1,0,0,0,0,1,1,1,0],"Secondary":[.1,.5,.1,.9,.4,.1,.3,.3,.3,.4,.4],"Final":[1.1,2.2,3.3,4.4,5.5,6.6,7.7,8.8,9.9,10.10,11.11]})
df.sort_values(['First','Test','Secondary','Final'],ascending=False, inplace=True)
index_subset=df[df["Test"]==0].index
sorted_subset=df[df["Test"]==0].sort_values(['First','Final'],ascending=False)
df.loc[index_subset,:]=sorted_subset.values
print(df)