Adding elements to a list in for loop in R

Question

I'm trying to add elements to a list in a for loop. How can I set the field name?

L <- list() 
    for(i in 1:N)
    {
        # Create object Ps...
        string <- paste("element", i, sep="")
        L$get(string) <- Ps
    }

I want every element of the list to have the field name dependent from i (for example, the second element should have "element2")

How to do this? I think that my error is the usage of get

Rich Scriven · Accepted Answer · 2015-08-14 22:44:10Z

26

It seems like you're looking for a construct like the following:

N <- 3
x <- list()
for(i in 1:N) {
    Ps <- i  ## where i is whatever your Ps is
    x[[paste0("element", i)]] <- Ps
}
x
# $element1
# [1] 1
#
# $element2
# [1] 2
#
# $element3
# [1] 3

Although, if you know N beforehand, then it is better practice and more efficient to allocate x and then fill it rather than adding to the existing list.

N <- 3
x <- vector("list", N)
for(i in 1:N) {
    Ps <- i  ## where i is whatever your Ps is
    x[[i]] <- Ps
}
setNames(x, paste0("element", 1:N))
# $element1
# [1] 1
#
# $element2
# [1] 2
#
# $element3
# [1] 3

edited Aug 14, 2015 at 22:44

answered Nov 26, 2014 at 15:59

Rich Scriven

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2 Comments

Darko Over a year ago

Ok. I will do it. N is greater than 900, code will be more efficient

rrs Over a year ago

@HaddE.Nuff do you have any suggestions for the case were you don't know the size in advance. e.g., say the size is stochastic.

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