How to filter on aggregated data in Foundry Functions?

Question

I would like to know how can I filter on grouped data in Foundry Functions. I already managed to group and aggregate on my data, see below:

@Function()
    public async grouping(lowerBound : Integer ): Promise<TwoDimensionalAggregation<string>> {
        let grouping = Objects.search()
            .HospitalLosAnalysis()
            .groupBy(val => val['primaryHospitalName'].topValues())
            .count()

        //FILTER SHOULD BE HERE

        return grouping
    }

Now, I would like to filter only on rows, where the count is bigger than parameter lowerBound. The problem is I am not able to filter anymore as the grouping returns a TwoDimensionalAggregation, on which I am not able to filter anymore.

Some context: I would like to create a chart in Workshop where the user would be able to look only at hospitals with a significant count. He would input the lowerBound parameter in a textbox, and the function would remove all of the rows that are smaller than lowerBound.

Answer 1

You should be able to loop through the grouping variable. You can always check what is inside with an old console.log(grouping) and then preview.

It should look something like:

let newBuckets = [];
grouping.buckets.forEach(bucket => {
     if (bucket.value > lowerBound) {
         newBuckets = bucket
     }
});

grouping.buckets = newBuckets;

don't forget to add an await on your let grouping = await Objects.search..etcetc..count()

Answer 2

Assuming what you're looking for here is to filter on the result of the aggregation - otherwise, just filter the incoming data first before aggregating.

Once you've done your TwoDimensionalAggregation, you'll have a typescript data structure of that is a list of "buckets" where each bucket has a key and a value property. The key can be complex (i.e. if you groupBy a numeric, date, or timestamp property and have a range for a key) or simple, as in your case, where the key would be the primaryHospitalName.

So you'll have something like:

`grouping.buckets[0].key === "hospitalName1"`
`grouping.buckets[0].value === N`

You can easily filter this list of buckets any number of ways: something trivial like:

const filteredGrouping = {
    buckets = grouping.buckets.filter(e => e.value >= lowerBound)
}

Then return filteredGrouping instead of grouping. There's potentially relevant documentation about how to Create a custom aggregation here: https://www.palantir.com/docs/foundry/functions/create-custom-aggregation/