R: Cannot Open File : No such file or directory - r

Question

I have script as below:
setwd ("I:/prep/Coord/RData/test")
#load .csv files
a.files <- grep("^Whirr", dir(), value=TRUE) #pattern matching
b.files <- paste0("Files_", a.files)
for(i in length(a.files)){
a <- read.table(a.files[i], header=T, sep=",", row.names=1) #read files start with Whirr_
b <- read.table(b.files[i], header=T, sep=",", row.names=1) #read files start with Files_
a
b
cr <- as.matrix(a) %*% as.matrix(t(a)
cr
diag(cr)<-0
cr
#write to file
write.csv(cr, paste0("CR_", a.files[i], ".csv"))
}
Basically, what I want to do is to compare two files which have similar filename at the end of file name, and do the calculation, and write the result to file.
When I tried to print a.files and b.files, the output seems ok for me. The output as below:
> a.files <- grep("^Whirr", dir(), value=TRUE) #pattern matching
> b.files <- paste0("Files_", a.files, sep="")
Error: could not find function "paste0"
> a.files
[1] "Whirr_127.csv" "Whirr_128.csv"
> b.files
[1] "Files_ Whirr_127.csv" "Files_ Whirr_128.csv"
>
I tried to feed the script with multiple files, but I got an error msg as below:
Error in file(file, "rt") : cannot open the connection
In addition: Warning message:
In file(file, "rt") : cannot open file 'Files_ Whirr_128.csv': No such file or directory
So, I tried to use file.choose, but it also doesn't work for me.
Appreciate help from the expert

Answer 1

Change the line:
b.files <- paste0("Files_", a.files)
to:
b.files <- paste("Files_", a.files, sep="")
You are using a version of R that does not have paste0 (I see that code was given to you in an earlier answer). This means you were keeping an earlier version of b.files, perhaps one that had been constructed using paste.
One important lesson about this is that whenever you get an error message about a line, such as Error: could not find function "paste0", that means the line did not happen! You have to fix that error before you paste the code, or tell us about the error when you do- otherwise we assume the b.files <- paste0("Files_", a.files) line works.