Sequential adding of n elements-CodePudding

I ran into a problem in R where I need to manipulate a vector in R.

Lets say I have a vector of length 12:

vector <- c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)

I now need to add the elements 1 2, 3 4, 5 6 etc. into a new vector, in the example that would be:

newvector <- c(3, 7, 11, 15, 19, 23)

I need to do the same for longer sequences, such that it adds the first three, then 4-6, then 7-9 etc.

newvector <- c(6, 15, 24, 33)

and so on.

CodePudding user response：

One option could be:

tapply(x, cumsum(seq_along(x) %% 2 == 1), sum)

 1  2  3  4  5  6 
 3  7 11 15 19 23

for n = 3:

tapply(x, cumsum(seq_along(x) %% 3 == 1), sum)

 1  2  3  4 
 6 15 24 33

CodePudding user response：

Put the vector in a matrix and then use colSums. Here's a function to do that.

vector <- c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)

calculate_sum <- function(v, n) {
  colSums(matrix(v, nrow = n))
}

calculate_sum(vector, 2)
#[1]  3  7 11 15 19 23

calculate_sum(vector, 3)
#[1]  6 15 24 33

CodePudding user response：

I would do this: split splits the vector into n groups, and Reduce sums the n-th elements of each group.

newvector <- Reduce(` `, split(vector,c(1,2)))
[1]  3  7 11 15 19 23

As a function, you could have this:

splitSum <- function(vector,groups) Reduce(` `, split(vector,c(1:groups))) 
splitSum(vector,3)
[1]  6 15 24 33

CodePudding user response：

v <- 1:12

v1 <- rep(0, ((length(v))/2))

for(i in 1:((length(v))/2))
v1[i] <- v[i] v[i 1]

v1

I simply used a for loop. Perhaps checking if the vector length can be split into groups of 2 and 3 elements before with an if conditional may improve this...