CODEWITHSUNDEEP
rmatchsubsetdata-manipulation
John L. Godlee
John L. Godlee

Reputation: 601

Create new vector from row index of two matching columns

I have a data frame:

a <- c(1,2,3,4,5,6)

b <- c(1,2,1,2,1,4)

c <- c("A", "B", "C", "D", "E", "F")

df <- data.frame(a,b,c)

What I want to do, is create another vector d, which contains the value of c in the row of a which matches each value of b

So my new vector would look like this:

d <- c("A", "B", "A", "B", "A", "D")

As an example, the final value of b is 4, which matches with the 4th row of a, so the value of d is the 4th row of c, which is "D".

Upvotes: 2

Views: 46

Answers (2)

MKR
MKR

Reputation: 20095

Another option is to convert to factor and use it as:

factor(a, labels = c)[b]
#[1] A B A B A D

OR

as.character(factor(a, labels = c)[b])
#[1] "A" "B" "A" "B" "A" "D"

data

a <- c(1,2,3,4,5,6)

b <- c(1,2,1,2,1,4)

c <- c("A", "B", "C", "D", "E", "F")

Upvotes: 0

jasbner
jasbner

Reputation: 2283

If a and b are both lists with integer values you can use them directly.

d <- c[b[a]]
d
[1] "A" "B" "A" "B" "A" "D"

if a is a regular integer sequence along c you can simply call c from b.

c[b]
[1] "A" "B" "A" "B" "A" "D"

Upvotes: 8

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