R - get values from multiple variables in the environment - r

Question

I have some variables in my current R environment:
ls()
[1] "clt.list" "commands.list" "dirs.list" "eq" "hurs.list" "mlist" "prec.list" "temp.list" "vars"
[10] "vars.list" "wind.list"
where each one of the variables "clt.list", "hurs.list", "prec.list", "temp.list" and "wind.list" is a (huge) list of strings.
For example:
clt.list[1:20]
[1] "clt_Amon_ACCESS1-0_historical_r1i1p1_185001-200512.nc" "clt_Amon_ACCESS1-3_historical_r1i1p1_185001-200512.nc"
[3] "clt_Amon_bcc-csm1-1_historical_r1i1p1_185001-201212.nc" "clt_Amon_bcc-csm1-1-m_historical_r1i1p1_185001-201212.nc"
[5] "clt_Amon_BNU-ESM_historical_r1i1p1_185001-200512.nc" "clt_Amon_CanESM2_historical_r1i1p1_185001-200512.nc"
[7] "clt_Amon_CCSM4_historical_r1i1p1_185001-200512.nc" "clt_Amon_CESM1-BGC_historical_r1i1p1_185001-200512.nc"
[9] "clt_Amon_CESM1-CAM5_historical_r1i1p1_185001-200512.nc" "clt_Amon_CESM1-CAM5-1-FV2_historical_r1i1p1_185001-200512.nc"
[11] "clt_Amon_CESM1-FASTCHEM_historical_r1i1p1_185001-200512.nc" "clt_Amon_CESM1-WACCM_historical_r1i1p1_185001-200512.nc"
[13] "clt_Amon_CMCC-CESM_historical_r1i1p1_190001-190412.nc" "clt_Amon_CMCC-CESM_historical_r1i1p1_190001-200512.nc"
[15] "clt_Amon_CMCC-CESM_historical_r1i1p1_190501-190912.nc" "clt_Amon_CMCC-CESM_historical_r1i1p1_191001-191412.nc"
[17] "clt_Amon_CMCC-CESM_historical_r1i1p1_191501-191912.nc" "clt_Amon_CMCC-CESM_historical_r1i1p1_192001-192412.nc"
[19] "clt_Amon_CMCC-CESM_historical_r1i1p1_192501-192912.nc" "clt_Amon_CMCC-CESM_historical_r1i1p1_193001-193412.nc"
What I need to do is extract the subset of the string that is between "Amon_" and "_historical".
I can do this for a single variable, as shown here:
levels(as.factor(sub(".*?Amon_(.*?)_historical.*", "\\1", clt.list[1:20])))
[1] "ACCESS1-0" "ACCESS1-3" "bcc-csm1-1" "bcc-csm1-1-m" "BNU-ESM" "CanESM2" "CCSM4"
[8] "CESM1-BGC" "CESM1-CAM5" "CESM1-CAM5-1-FV2" "CESM1-FASTCHEM" "CESM1-WACCM" "CMCC-CESM"
However, what I'd like to do is to run the command above for all the five variables at once. Instead of using just "ctl.list" as argument in the command above, I'd like to use all variables "clt.list", "hurs.list", "prec.list", "temp.list" and "wind.list" at once.
How can I do that?
Many thanks in advance!

Answer 1

You can put your operation into a function and then iterate over it:
get_my_substr <- function(vecname)
levels(as.factor(sub(".*?Amon_(.*?)_historical.*", "\\1", get(vecname))))
lapply(my_vecnames,get_my_substr)
lapply acts like a loop. You can create your list of vector names with
my_vecnames <- ls(pattern=".list$")
It is generally good practice to post a reproducible example in your question. Since none was provided here, I tested this approach with...
# example-maker
prestr <- "grr_Amon_"
posstr <- "_historical_zzz"
make_ex <- function()
replicate(
sample(10,1),
paste0(prestr,paste0(sample(LETTERS,sample(5,1)),collapse=""),posstr)
)
# make a couple examples
set.seed(1)
m01 <- make_ex()
m02 <- make_ex()
# test result
lapply(ls(pattern="^m[0-9][0-9]$"),get_my_substr)

Answer 2

One solution would be to create a vector containing the variable names that you want extract the data from, for example:
var.names <- c("clt.list", "commands.list", "dirs.list")
Then to access the value of each variable from the name:
for (var.name in var.names) {
var.value <- as.list(environment())[[var.name]]
# Do something with var.value
}