I have two dataframes, the main dataframe has two columns for Lat and Long some of which have values and some of which are NaN. I have another dataframe that is a subset of this main dataframe with Lat and Long filled in with values. I'd like to fill in the main DataFrame with these values based on matching ID.
Main DataFrame:
ID Lat Long
0 9547507704 33.853682 -80.369867
1 9777677704 32.942332 -80.066165
2 5791407702 47.636067 -122.302559
3 6223567700 34.224719 -117.372550
4 9662437702 42.521828 -82.913680
... ... ... ...
968552 4395967002 NaN NaN
968553 6985647108 NaN NaN
968554 7996438405 NaN NaN
968555 9054647103 NaN NaN
968556 9184687004 NaN NaN
DataFrame to fill:
ID Lat Long
0 2392497107 36.824257 -76.272486
1 2649457102 37.633918 -77.507746
2 2952437110 37.511077 -77.528711
3 3379937304 39.119430 -77.569008
4 3773127208 36.909731 -76.070420
... ... ... ...
23263 9512327001 37.371059 -79.194838
23264 9677417002 38.406665 -78.913133
23265 9715167306 38.761194 -77.454184
23266 9767568404 37.022287 -76.319882
23267 9872047407 38.823017 -77.057818
The two dataframes are of different lengths.
EDIT for clarification: I need to replace the NaN in the Lat & Long columns of the main DataFrame with the Lat & Long from the subset if ID matches in both DataFrames. My DataFrames are both >60 columns, I am only trying to replace the NaN for those two columns.
Edit:
I went with this mapping solution although it isn't exactly what I'm looking for, I know there is a much more simple solution.
#mapping coordinates to NaN values in main
m = dict(zip(fill_df.ID,fill_df.Lat))
main_df.Lat = main_df.Lat.fillna(main_df.ID.map(m))
n = dict(zip(fill_df.ID,fill_df.Long))
main_df.Long = main_df.Long.fillna(main_df.ID.map(n))
CodePudding user response:
new_df = pd.merge(main_df, sub_df, how='left', on='ID')
I guess the left join will do the job.
CodePudding user response:
One approach is to use DataFrame.combine_first
. This method aligns DataFrames on index and columns, so you need to set ID
as the index of each DataFrame, call df_main.combine_first(df_filler)
, then reset ID
back into a column. (Seems awkward; there's probably a more elegant approach.)
Assuming your main DataFrame is named df_main
and your DataFrame to fill is named df_filler
:
df_main.set_index('ID').combine_first(df_filler.set_index('ID')).reset_index()
CodePudding user response:
This should do the trick:
import math
A = pd.DataFrame({'ID' : [1, 2, 3], 'Lat':[4, 5, 6], 'Long': [7, 8, float('nan')]})
B = pd.DataFrame({'ID' : [2, 3], 'Lat':[5, 6], 'Long': [8, 9]})
print('Old table:')
print(A)
print('Fix table:')
print(B)
for i in A.index.to_list():
for j in B.index.to_list():
if not A['ID'][i] == B['ID'][j]:
continue
if math.isnan(A['Lat'][i]):
A.at[i, 'Lat'] = B['Lat'][j]
if math.isnan(A['Long'][i]):
A.at[i, 'Long'] = B['Long'][j]
print('New table:')
print(A)
Returns:
ID Lat Long
0 1 4 7.0
1 2 5 8.0
2 3 6 NaN
Fix table:
ID Lat Long
0 2 5 8
1 3 6 9
New table:
ID Lat Long
0 1 4 7.0
1 2 5 8.0
2 3 6 9.0
Not very elegant but gets the job done :)
CodePudding user response:
A.set_index('ID').fillna(B[['ID', 'Lat', 'Long']].set_index('ID')).reset_index()
Example:
>>> A
ID Lat Long Dont Update
0 1 4 7.0 7.0
1 2 5 8.0 8.0
2 3 6 NaN NaN
>>> B
ID Lat Long Dont Update
0 2 5 8 10
1 3 6 9 10
>>> A.set_index('ID').fillna(B[['ID', 'Lat', 'Long']].set_index('ID')).reset_index()
ID Lat Long Dont Update
0 1 4 7.0 7.0
1 2 5 8.0 8.0
2 3 6 9.0 NaN