Calling variable in the loop by using assign and paste0 - r

Question

I have a variable named SAL_mean created like this (I want to make a loop once I figure this out):
watersheds <- c('ANE', 'SAL', 'CER')
assign(paste0(watersheds[1], '_mean'), read.csv(paste0(watersheds[1], '_mean.csv')))
now the next step should be something like this (which works):
cols_dont_want <- c('B1', 'B2', 'B3')
assign(paste0(watersheds[1], '_mean'), SAL_mean[, !names(SAL_mean) %in% cols_dont_want])
but I wanted to ask how to replace "SAL_mean" by using watersheds[1], because this line of code doesn't work:
assign(paste0(watersheds[1], '_mean'), paste0(watersheds[1], '_mean')[, !names(paste0(watersheds[1], '_mean')) %in% cols_dont_want])
I think it treats the "paste0(watersheds[2], '_mean')" as string and not as a name of variable but I haven't been able to find a solution (I tried for example "as.name" function but it gave me an error "object of type 'symbol' is not subsettable")

Answer 1

Keep dataframes in a list using ?lapply, then it gets easier to carry out same transformations on multiple dataframes in a list, something like:
# set vars
watersheds <- c('ANE', 'SAL', 'CER')
cols_dont_want <- c('B1', 'B2', 'B3')
# result, all dataframes in one list
myList <- lapply(watersheds, function(i){
# read the file
x <- read.csv(paste0(i, "_mean.csv"))
# exclude columns and return
x[, !colnames(x) %in% cols_dont_want]
} )

Answer 2

replace
paste0(watersheds[2], '_mean')
with
eval(parse(text = paste0(watersheds[2], '_mean')))
and it should work. Your guess is correct, paste0 just gives you a string but you need to call the variable which is done using eval()

Answer 3

Or you can do it in a for loop (some find the syntax more understandable). It's equivalent to zx8754's solution, except it assigns names to each dataframe as per the OP. It's trivial to modify zx8754's solution do do the same.
watersheds <- c('ANE', 'SAL', 'CER')
cols_dont_want <- c('B1', 'B2', 'B3')
ws.list <- list()
for (i in 1:length(watersheds)) {
ws.list[[i]] <- read.csv(paste0(watersheds[i], '_mean.csv'))
names(ws.list)[i] <- paste0(watersheds[i], '_mean')
ws.list[[i]] <- ws.list[[i]][!names(ws.list[[i]]) %in% cols_dont_want]
}
names(ws.list)
# "ANE_mean" "SAL_mean" "CER_mean"
# If you absolutely want to call the data.frames by their
# individual names, you can do so after you attach() the list.
attach(ws.list)
ANE_mean