Dear all

I have a question about summing groups of cells in the spreadsheet. Basically, I have the following data format:

group | value
1 | 2.0
1| 2.1
1 | 2.3
1 | 1.1
2 | 2.1
2 | 3.1
3 | 4.2
3 | 2.3
3 | 3.2
4 | 5.1
4 | 4.9
4 | 3.1
5 | 2.9
5 | 1.8
6 | 1.2
6 | 2.1
6 | 2.3

and it goes on to thousands.
I want to get the total of say, group 1-3; group 4-6, 7-9, etc

the anticipated outcome would be

reduced group | total
A (which is 1-3) | x
B (which is 4-6) | y
C (which is 7-9) | z


How can I do that?

many thanks for your help!