[R] cumulative sum in data frame

[SEUNG CHEON HONG]

Dear R-Help List,

I have a question about data manipulation. I tried to make code myself but too much for me. I would greatly appreciate your help.

I have data set consisting of site (from 1 to N1) and distance and there are several variables (1 to N2) collected from each sampling site. I am interested in looking at cumulative sums of each variable based on site and distance like below. 

Can anyone help create function to do the task? The cumulative sum outputs may not be necessarily combined with original data. It will be better to have only cumulative sum outputs and indicator variables of interest.

site	distance	var1	…	var(n2)	cu.sum.v1	…	cu.sum.v(n2)
1	10	1		0	1		0
1	20	0		1	1		1
1	30	1		2	2		3
1	40	3		3	5		6
1	50	1		4	6		10
2	10	1		1	1		1
2	20	2		1	3		2
2	30	4		1	7		3
2	40	0		1	7		4
2	50	1		1	8		5
,,,	,,,	,,,	,,,	,,,			
n1	10	1		1	1		1
n1	20	1		0	2		1
n1	30	1		1	3		2
n1	40	1		0	4		2
n1	50	1		1	5		3


Thank you very much for reading and time!!!

Steve Hong