[R] Summing rows by years (each time separately)

[Andrew Gaska]

Dear all,

I could not find an answer for the problem.

I have a matrix and I want to sum rows in groups i.e. rows are summed as
long as rows of column 1 have some value (f.e. 2008 in it), then again rows
are summed as long as rows of column 2 have some value (f.e. 2009 in it). 

In case there is a repetition of value in column 1 in another group, this
group should be summed seperately.

Example: 

I have such a matrix:

 *1.2008*	3	2	2
 *2.2008*	4	3	3
* 3.2008*	5	4	4
* 4.2008*	3	3	1
 *1.2009*	6	1	2
 *2.2009*	3	2	5
 *1.2010*	4	4	3
* 2.2010*	3	3	2
 *3.2010*	1	5	3
 *4.2010*	2	2	2
* 1.2008*	3	1	1
 *2.2008*	4	3	2
 *3.2008*	2	4	3
 *1.2009*	1	2	4
 *2.2009*	5	4	3
 *3.2009*	4	3	3
 *1.2010*	4	3	1
 *2.2010*	2	2	2

The result should be like this:

*2008*	15	12	10
*2009*	9	3	7
*2010*	10	14	10
*2008*	9	8	6
*2009*	10	9	10
*2010*	6	5	3


Could You help me with that?

Yours,
Andrew Gaska


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