Categorised data in PowerBi

Question

I'd like some advice on how to categorize/group data in PowerBi.

For example, I set up a conditional column in Power Query to achieve the results seen in the "Group" column by saying if ID is 8304, then Group B, and if ID is 8660, then Group F — but the database is large, and I'm already experiencing performance issues when trying to set up a report based on individual Groups; the data takes a long time to load.

Is there a better or more efficient way to group data?

ID	Group
8015	A
8020	A
8229	A
8304	B
8389	B
8391	C
8414	D
8421	A
8469	A
8572	A
8619	F
8660	F
8663	J
9102	A
9104	K
9120	A