[R] using variable from for loop in naming new variables

[Joshua Wiley]

Dear Jim,

Just to follow up some of the great suggestions with some examples:

#########################################

# Initialize a list, length 4
lstuff <- vector(mode = "list", length = 4)
# store the results of your for loop in it
for (i in 1:4) {
  lstuff[[i]] <- 3 + i
}

# The assign() way
for(i in 1:4) {
  assign(x = paste("stuff", i, sep = ''),
         value = 3 + i, envir = .GlobalEnv)
}

# Now lets see about accessing the data
stuff1
lstuff[[1]]
lstuff # see all elements of the list at once

# So far, so good, but since they are named similarly
# maybe I want to do a similar operation on all of them

# Using the list

lstuff <- lapply(lstuff, '+', y = 3)

# Using the results of the for loop
# stuff1 <- stuff1 + 3
# for every single one, or...

for(i in 1:4) {
  assign(x = paste("stuff", i, sep = ''),
         value = get(paste("stuff", i, sep ='')) + 3,
         envir = .GlobalEnv)
}

# looking again

stuff1
lstuff[[1]]

# if you are concerned because the real thing is  more complex

lstuff[[1]] <- data.frame(A = 1:10, B = 11:20)
lstuff[[2]] <- matrix(rnorm(10))
# you can store much more complex objects in the list
# so no need to worry if "stuff" is actually going to be
# data frames or tables or ...

################################################

Cheers,

Josh

On Thu, Sep 16, 2010 at 8:44 AM, Maas James Dr (MED) <J.Maas at uea.ac.uk> wrote:
> Simple one here ... but can't get it to work ...
>
> for (i in 1:4){
>    paste("stuff",[i]),sep="") <- 3 + i
> }
>
> ls()
> rm(list=ls())
>
>
>
> I just want it to create 4 new variables called stuff1, stuff2, stuff3, stuff4 with the corresponding assignments.  I realise that there are more elegant functions but this is just a model of a bigger situation.
>
> Thanks
>
> Jim
>
>
> ===============================
> Dr. Jim Maas
> University of East Anglia
>
>
>        [[alternative HTML version deleted]]
>
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>



-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/