R - Add Column w/ File Name on For Loop - r

Question

I use assing in a for loop to batch read in all the .csv files in a working directory. I then use substr to clean the names of the files. I would like to add a column to each of the files with the file name for better analysis later in the code. However, I am having trouble referencing the file in the for loopafter the file names have been cleaned to add a column.
#read in all files in folder
files <- list.files(pattern = "*.csv")
for (i in 1:length(files)){
assign(substr(files[i], start = 11, stop = nchar(files[i])-4), #clean file names
read.csv(files[i], stringsAsFactors = FALSE))
substr(files[i], start = 11, stop = nchar(files[i])-4)['FileFrom'] <- files[i]
}

Answer 1

assign does not seem to be the right function here, I think you need to use eval(parse()) on a string cmd that you set up. The inline notes explain more:
# read in all files in folder
files <- list.files(pattern = "*.csv")
# loop through the files
for (i in 1:length(files)){
# save the clean filename as a char var because it will be called again
fnClean = substr(files[i], start = 1, stop = nchar(files[i])-4)
# create a cmd as a string to be parsed and evaluated on-the-fly
# the point here is that you can use the 'fnClean' var in the string
# without knowing what it is - assign is expecting an inline string
# ...not a string saved as a var, so it can't be used in this case
loadFileCMD = paste0(fnClean,' = read.csv(files[i], stringsAsFactors =
FALSE)')
print(loadFileCMD) # check the cmd
eval(parse(text=loadFileCMD))
# create another string command to be evaluated to insert the file name
# to the 'FileFrom' field
addFnCMD = paste0(fnClean,'$FileFrom = files[i]')
print(addFnCMD) # check the cmd
eval(parse(text=addFnCMD))
}

Answer 2

Would this work?
#read in all files in folder
files <- list.files(pattern = "*.csv")
filesCopy <- files
for (i in 1:length(files)){
assign(substr(files[i], start = 11, stop = nchar(files[i])-4), #clean file names
read.csv(files[i], stringsAsFactors = FALSE))
substr(files[i], start = 11, stop = nchar(files[i])-4)['FileFrom'] <- filesCopy[i]
}