R Error in for loop

Question

I would like to make several lists of numbers and then concatenate them i.e.

list 1 = 1, 1, 1, 1

list 2 = 2, 2, 2, 2

list 3 = 3, 3, 3, 3

final list = 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3

I tried the following to create lists 1 to 3

ageseq <- c(1,2,3)
n <- 3
n2 <- 4

for (i in 1:n){
  for (j in 1:n){
    age[i] <- c(rep(ageseq[j],n2))
  }  
}

which produces the following error,

In age[i] <- c(rep(ageseq[j], n2)) :
  number of items to replace is not a multiple of replacement length

as age1, age2 and age3 do not exist.

What in my code is missing? In reality I need to concatenate over 70 lists of numbers.

The age object should be a list of length n2. I would then like to concatenate these n lists of length n2 to form a list of length 3n2. In reality n2 = >30 and n>70. — user2568648
– user2568648, Commented Oct 2, 2015 at 16:01
Thanks nicola. So simple! I had previously tried rep(1:3,4) and did not know about each. — user2568648
– user2568648, Commented Oct 2, 2015 at 16:04

JCollerton · Accepted Answer · 2015-10-02 16:34:51Z

3

So the problem is that you are replacing an element of length one (age[i]) with an element of length four (rep(ageseq[j], n2)). You aren't concatenating the lists, you're trying to replace the number i element with a list of numbers, which leads to the warnings.

If you want to do it the way you've specified, you need to use the loop:

ageseq <- c(1,2,3)
n <- 3
n2 <- 4
age <- c()

for (j in 1:n){
  age <- c(age, rep(ageseq[j],n2))
}

Which will concatenate the separate lists into one as you wanted. Another option as someone put before is to use: age <- rep(1:3,each=4). To create the separate lists you could use the loop:

ageseq <- c(1,2,3)
n <- 3
n2 <- 4
age_list <- list()

for (j in 1:n){
  age_list[[j]] <- rep(ageseq[j],n2)
}

Then age_list[[1]] will be a list of ones, age_list[[2]] will be a list of twos etc.

answered Oct 2, 2015 at 16:34

JCollerton

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cd1 · Accepted Answer · 2015-10-02 17:44:28Z

0

You can try:

unlist(lapply(1:3, rep, 4))

answered Oct 2, 2015 at 17:44

cd1

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