How to sum vector elements with the same name in R?

Question

Most solutions I found were for data frames or lists, not for vectors.

From: myvec = c(A=2, B=2, A=2)

To: desiredvec = c(A=4, B=2)

Answer 1

You can use tapply

> tapply(myvec, names(myvec), sum)
A B
4 2

or xtabs

> xtabs(myvec~names(myvec))
names(myvec)
A B
4 2

Answer 2

You can use rowsum :

rowsum(myvec, names(myvec))
#  [,1]
#A    4
#B    2

rowsum returns a matrix. If you need a vector.

rowsum(myvec, names(myvec))[, 1]
#A B 
#4 2 

Answer 3

Define:

splitbyitsnames <- function(namedVec) { # split a list by its names
  stopif(is.null(names(namedVec)), message = "NO NAMES")
  split(namedVec, f = names(namedVec))
}

unlapply <- function (...) { unlist(lapply(...)) } # lapply, then unlist

sumBySameName <- function(namedVec) { # Sum up vector elements with the same name
  unlapply(splitbyitsnames(namedVec), sum)
}

From CodeAndRoll

Call:

> sumBySameName(myvec)
A B 
4 2 

Please add if there is a better solution

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Answer 4

Using aggregate/stack

aggregate(values ~ ., stack(myvec), sum)