Add two vectors by name

I have two named vectors

v1 <- 1:4
v2 <- 3:5
names(v1) <- c("a","b","c","d")
names(v2) <- c("c","e","d")

I want to add names to them, that is, the expected result is

> v3  
a b c d e   
1 2 6 9 4

Is there any way to do this programmatically in R? Note that the name may not necessarily be the sort order, such as v2. 0 above

Solution

Just combine the vectors (for example, use C) and use auto fill:

v3 <- c(v1,v2)
tapply(v3,names(v3),sum)
# a b c d e 
# 1 2 6 9 4

Or, for fun (because you're just doing summation), continue "V3":

xtabs(v3 ~ names(v3))
# names(v3)
# a b c d e 
# 1 2 6 9 4

I think you can also use "data. Table":

library(data.table)
as.data.table(Reduce(c,mget(ls(pattern = "v\\d"))),keep.rownames = TRUE)[,list(V2 = sum(V2)),by = V1]
#    V1 V2
# 1:  a  1
# 2:  b  2
# 3:  c  6
# 4:  d  9
# 5:  e  4

(what I share is not "data. Table", but an automated way to capture vectors of interest.)