GroupBy using grouper function that returns complex type doesn not work

When performing a GroupBy on a List<<T>> using a grouper function that returns a “complex” anonymous type, GroupBy returns a flat array of objects (untyped “T” objects) instead of a list of key/value pairs as it does when grouping with a grouper function that returns a primitive type.

e.g with a type.

interface IReferral {
    origin: string;
    modalityType: string;
    qtyReferrals: number;
}

Not working:

let referralsByOrigin = new List<IReferral>(data).GroupBy(key => ({ org: key.origin, modType: key.modalityType}), element => element);

I am currently working around this by creating a primitive returning grouper that returns a concatenation of my grouping elements like below, and then, when processing the result, retrieving the actual grouping elements from the first item. (instead of retrieving them as “menbers” of the grouper result (key) :

let groupedData = new List<IReferral>(result).GroupBy(key => key.origin + '_' + key.modalityType , element => element);

for (var key in groupedData) {
  // count the total nr of referrals
  var totalReferrals = groupedData[key].reduce((a, b) => a + b.qtyReferrals, 0);
  var firstItem : IReferral = new List<IReferral> (groupedData[key]).First();
  this.chartData.push([firstItem.origin, firstItem.modalityType, totalReferrals]);
}

a fix to this would be great!

[marlon-tucker]

This will never work, the object being returned is “new” and therefore always unique. In C# I believe this works due to anonymous objects implementing a simplistic IEquality interface which hashes the properties. This is not achievable in javascript.

You could inspect the mapped return type to see if it contains a “equals” function, and use the return value from that function instead, but in that case, the mapping function is better placed to call it instead.

In short, this is not achievable with the current set of tools javascript provides.

[kutyel]

I’ll close this for now since as discussed in the thread I don’t think this is possible yet due to the nature of JavaScript itself 🤷‍♂️