I have a large dataset ~1mln rows, and about 5000 absent coordinates(i’d like to fill them with median value by category ‘city’everything but fillna is working, how to make it happen?
city = ['London', 'Paris', 'Vienna', 'Milan','London', 'Paris', 'Vienna', 'Milan'] lat = [51.510843900000005, 48.8671391, 48.204465500000005, 45.4787357, 51.510843900000005, 48.8671391, None, None] lng = [-0.1424476, 2.328075, 16.3686397, 9.1961308, -0.14244, 2.329, None, None] data = pd.DataFrame(list(zip(city, lat, lng)),columns =['city', 'lat', 'lng']) display(data['lat'].isna().sum()) # 2 display(data['lng'].isna().sum()) # 2 for city_name in set(data['city']): data[data['city'] == city_name ]['lat'].fillna(data[data['city'] == city_name ]['lat'].median()) data[data['city'] == city_name ]['lng'].fillna(data[data['city'] == city_name ]['lng'].median()) print(city_name, data[data['city'] == city_name ]['lat'].median(),data[data['city'] == city_name ]['lng'].median()) display(data['lat'].isna().sum()) # 2 display(data['lng'].isna().sum()) # 2
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Answer
You could do:
data.groupby("city").transform(lambda x: x.fillna(x.median()))
First groupby with the city, then use transform with fillna and calculate the median. (you could use any mathematical operation)