Joining lists into a vector

Question

I want to create the following vector using a, b, c repeating each letter thrice:

BB<-c("a","a","a","b","b","b","c","c","c")

This is my code:

Alphabet<-c("a","b","c")
AA<-list()
for(i in 1:3){
  AA[[i]]<-rep(Alphabet[i],each=3)
}
BB<-do.call(rbind,AA)

But I am getting a dataframe:

    dput(BB)
structure(c("a", "b", "c", "a", "b", "c", "a", "b", "c"), .Dim = c(3L, 
3L))

What I am doing wrong?

Use the `each` argument `rep(Alphabet, each = 3)` – akrun Nov 15 '16 at 12:07 — akrun, Nov 15 '16 at 12:07

score 1 · Accepted Answer · answered Nov 15 '16 at 12:13

As Akrun mentioned we can use the same rep function create a vector which consists of letters a,b,c

A <- c("A","B","C")

Apply rep function for the same vector, use each as sub function

AA <- rep(A,each=3)

print(AA)

[1] "A" "A" "A" "B" "B" "B" "C" "C" "C"

score 1 · Answer 2 · answered Nov 15 '16 at 12:16

1

You should use c function to concatenate, not the rbind. This will give you vector.

Alphabet<-c("a","b","c")
AA<-list()
for(i in 1:3){
  AA[[i]]<-rep(Alphabet[i],each=3)
}
BB<-do.call(c,AA)

Akrun comment is also true, if thats what you want.

answered Nov 15 '16 at 12:16

Kumar Manglam

score 1 · Answer 3 · answered Nov 15 '16 at 12:27

1

You can also concatenate the rep function like so: BB <- c(rep("a", 3), rep("b", 3), rep("c", 3))

answered Nov 15 '16 at 12:27

ringgord

Thanks for response. +1 for the trick. Actually I had a long list containing names, and I wanted to create a vector repeating each one consecutively for a certain number of times. – runjumpfly Nov 15 '16 at 12:34

score 0 · Answer 4 · answered Nov 15 '16 at 12:12

0

Here is a solution but note this form or appending is not efficient for large input arrays

Alphabet <- c("a","b","c")
bb <- c()
for (i in 1:length(Alphabet)) {
  bb <- c(bb, rep(Alphabet[i], 3))
}

answered Nov 15 '16 at 12:12

Dirk Nachbar

Please, do not encourage newbies to use for loops in R whenthere are vectorized functions available, e.g, `rep(c("A","B","C"), each=3)` - Thank you. – Uwe Nov 15 '16 at 12:43

4 Answers4