# Filtering of maximum value by ID and category sum

I have a task that is quite simple: I need to get the sum of values in the categories of each ID, and keep the category with the highest sum:

id    category   value
1       A         10
1       A         15
1       B         13
2       A         80


So, in this case the sum of value for each category-id pair would be:

id    category   value
1       A         25
1       B         13
2       A         80


And then the maximum for id == 1 is 25 and for the other is 80, so the final dataframe is:

id    category   value
1       A         25
2       A         80


I achieved this like this:

(df.groupby(['id', 'category'])['value']
.sum().reset_index().sort_values(by=['id', 'value'])
.drop_duplicates(['id'], keep='last'))


I feel this can be done in lesser steps, maybe with some transform, but I can't find a better way. Any ideas?

Thanks

## 1 Answer

You could also do the following. Compute the first grouping by id and category, sum up the values:

y = df.groupby(["id","category"])["value"].sum()


Afterwards, grab the best category according to your definition:

y.groupby("category").sum().nlargest(1)


Combining these, so that we get the full job done:

y = df.groupby(["id","category"])["value"].sum()
cat = y.groupby("category").sum().nlargest(1).index
y.loc[:,cat]

• I believe the original target was a max-sum category per id, rather than a single category overall? So y.loc[y.groupby('id').idxmax()] – GeoMatt22 Oct 15 '20 at 15:14