How to append many range of subset to a new dataframe after some filtering?

Question

I have a subset (type <class 'list'>) which contain many subdataframe(subset[0],subset[1],subset[2]......so on).I want to do some filtering on each subset and after filtering i want to append it to a new dataframe. My code:

new_df = pd.DataFrame()
for i in range(20):
     a = subsets[i]
     a = a[((a[f'RUT1_Ang_meas_{i}'] >= -1.047198) & (a[f'RUT1_Ang_meas_{i}'] <= 1.047198))]
     .
     .
     #some filtering
     .
     . 
     new_df= pd.concat([a],axis=1)

new_df.info() ```

i am getting an empty final dataframe.

How can i modify the code ?

Answer 1

Try this:

list1 = []  

# inside the loop:  
list1.append(a)
 
# after the loop  
new_df = pd.concat(list1, axis=1)