groupBy partial object creates issues with downstream usage.

[AndrewSouthpaw]

Here's a sample usage of groupBy:

it("test", () => {
  type Foo = { id: number; color: string };
  const byColor = groupBy(({ color }) => color, [
    { color: "red", id: 1 },
    { color: "blue", id: 2 },
    { color: "red", id: 3 },
  ] as Foo[]);
  Object.values(byColor).map((grouping: Foo[]) => {
    console.log(grouping);
  });
});

which triggers this error:

The map parameter needs to be supplied with Foo[] | undefined to work correctly, even though that's not the right type.

Removing the Partial wrapping the return type would fix this DX issue... I'm wondering what is the rationale for providing a partial record type?

[Harris-Miller]

The suggestion to add the Partial<> was made and merged in this MR: #45

Your issue has already been brought up and resolved. Please see here: #91

[AndrewSouthpaw]

Oh, sorry I didn't search for groupBy in the issues before posting! My bad, and thanks for the response. I'll move any subsequent questions there.