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sequential sum

4 messages · baccts, Nordlund, Dan (DSHS/RDA), David Winsemius +1 more

Original
baccts
# 
Dear R users,

I am trying to sum number that exist in another vector up to i, then
increment i and repeat.
Sorry. It's hard to explain but basically I am trying to do the following:
test <- c(1,2,3,4);
test2 <- c(3,5,6,7,2,8,8,4,4);
test3 <- c(10,20,30,40);
tmp <- 0;
for (i in 1:length(test)){
tmp[i] <- sum(test3[which(test[1:i] %in% test2)]);
}

so when i = 1, tmp[i] = 0 because test[1]=1 is not in test2 and
when i = 3, tmp[i] = 50 = test3[2] + test3[3] because test[2:3] is in test2

Problem is test has 5000+ entries. How do I do the same thing without the
loop?

Thanks in advance. 

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Nordlund, Dan (DSHS/RDA)
# 
Your example data is not very extensive so I don't know if this solution is general enough.  But, it does work with your data.

tmp <- cumsum(ifelse(test %in% test2, test3, 0))


Hope this is helpful,

Dan

Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204
David Winsemius
#
On Feb 14, 2012, at 1:38 PM, Nordlund, Dan (DSHS/RDA) wrote:

            

      
      
      
    

        
I had exactly that concern so tested my solution, which was a bit  
different than yours:

test <- c(1,2,3,4,10, 5);
test2 <- c(3,5,6,7,2,8,8,4,4);
test3 <- c(10,20,30,40, 50, 60);
tmp <- 0;
for (i in 1:length(test)){
tmp[i] <- sum(test3[which(test[1:i] %in% test2)]);
}

 > tmp
[1]   0  20  50  90  90 150
 > tmp2 <- ifelse(test %in% test2, cumsum(test3[test %in% test2]), 0)
 > tmp2
[1]   0  50  90 150   0  50  # was going to throw away.


 > tmp3 <- cumsum(ifelse(test %in% test2, test3, 0))
 > tmp3
[1]   0  20  50  90  90 150

So yours is better at spanning the non-match entries in the same  
manner as the for-loop.

            

      
      
      
    

        
David Winsemius, MD
West Hartford, CT