Hello,
I'd like to take all possible sub-summands of a vector in the quickest and
most efficient way possible. By "sub-summands" I mean for each sub-vector,
take its sum. Which is to say: if I had the vector
x<-1:4
I'd want the "sum" of x[1], x[2], etc. And then the sum of x[1:2], x[2:3],
etc. And then...so on.
The result would be:
1 2 3 4
2 5 7
6 9
10
I can do this with for loops (code below) but for long vectors (10^6
elements) looping takes more time than I'd like. Any suggestions?
Thanks very much in advance--
Andy
# calculate sums of all sub-vectors...
x <- 1:4
sub.vect <- vector("list",4)
for(t in 1:4) {
maxi <- 4 - t + 1
this.sub <- numeric(maxi)
for(i in 1:maxi) {
this.sub[i] <- sum(x[i:(i+t-1)])
}
sub.vect[[t]] <- this.sub
}
sub.vect
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