CODEWITHSUNDEEP
r
Kei
Kei

Reputation: 45

How do I add vectors of different lengths?

I am trying to add two vectors.

I tried just simply doing this

c <- a + b

The answer came out as 69, 10, 44, 6. I am guessing it reused a?

I want c to be 69, 10, 3, 1 after adding a and b together.

I have no experience with R at all so please keep the solution simple. Thanks in advance!

Upvotes: 2

Views: 818

Answers (3)

Juan Carlos Ramirez
Juan Carlos Ramirez

Reputation: 2129

When you add two vectors of different sizes, R recycles the one of shorter length. See: https://cran.r-project.org/doc/manuals/r-release/R-lang.html#Recycling-rules. One solution is to pad out the shorter one with zeros as in tmfmnk's answer.

Upvotes: 0

tmfmnk
tmfmnk

Reputation: 39858

Another possibility could be:

c(a, rep(0, length(b) - length(a))) + b

[1] 69 10  3  1

Upvotes: 3

akrun
akrun

Reputation: 887118

It is due to recycling. We can prevent it by keeping the lengths same, but adding 0's

a1 <- `length<-`(a, length(b))
replace(a1, is.na(a1), 0) + b
#[1] 69 10  3  1

Or if there are multiple vectors, place it in a list, set the length programmatically and use rowSums which also have the na.rm parameter

lst1 <- list(a, b)
rowSums(sapply(lst1, `length<-`, max(lengths(lst1))), na.rm = TRUE)
#[1] 69 10  3  1

Upvotes: 3

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