How sum in excel only for given value - excel

Question

I have in excel something like:
A B
1 Value1 10
2 Value2 20
3 Value1 5
4 Value1 10
5 Value2 15
How I can sum for given value in A? For example, having something like this:
6 C D
7 Value1 25 (sum of b1+b3+b4)
8 Value2 35 (sum of b2+b5)
Of course, how can I do this automatically and not manually.
Thanks very much.

Answer 1

Let's assume you have a list of the unique values in column A listed in column C, i.e.:
Row A B C
1 Value1 10 Value1
2 Value2 20 Value2
3 Value1 5
4 Value1 10
5 Value2 15
In column D, the following formula will count the occurences of each value in column C:
=SUMIF(A$2:A$6, "=" & $C2, B$2:B$6)
This should be pasted into D2 and then copied to D3, D4, etc.
The result will look like:
Row A B C D
1 Value1 10 Value1 25
2 Value2 20 Value2 35
3 Value1 5
4 Value1 10
5 Value2 15
How does this work? SUMIF allows criteria to be used, and if satisfied, a SUM of the cells is taken. In this case, the SUMIF does this:
Looks in cell range A$2:A$6
Compares the value in each cell to see if it is equal to $C2 (or $C3, etc dependent upon which row is being calculated)
If it is equal, sum the value from the cell range B$2:B$6
Limitations
In order for this to work, the unique values in column A must already be known and listed in column C. There are some ways of generating a list of unique values but they are not straight-forward. Roll on UNIQUE which ships with the new version of Office.

Answer 2

There are different ways to do this:
Use a pivot table (as already mentioned in the comments).
Use a SumIf() worksheet function (as mentioned in another answer). This, however, will only work if you know all names (like Value1, Value2, ... (the list MUST be limited))
Use subtotals. This, however, will only work when you sort first.
Write a VBA macro.