invalid path argument in R - r

Question

I had tried to execute this function to find correlation between two elements in the excel files of directory "specdata",by passing in the command line corr("specdata"). But it shows " Error in list.files(directory, full.names = TRUE) : invalid 'path' argument ". I had checked the current working directory and it was correct. Any ideas for the reason of error ?
corr <- function(directory , threshold=0){
files_all <- list.files( directory , full.names = TRUE )
v <- c(mode = "numeric" , length = 0 )
for ( i in 1:length(files_all)) {
individual <- read.csv(files_all[i] , head = TRUE )
nobs <- sum(complete.cases(individual))
if ( nobs > threshold ) {
xSulfate <- individual[which(!is.na(individual$sulfate)),]
yPollutant <- xSulfate[which(!is.na(xSulfate$nitrate)),]
v <- c( v , cor(yPollutant$sulfate,yPollutant$nitrate))
}
}
return v
}

Answer 1

The corr() function in the Johns Hopkins University R Programming course assignment makes the assumption that the specdata directory is a subdirectory of the current R working directory.
One way to retrieve the list of files from this subdirectory is to retrieve the current directory with getwd() and use this to build the full path to use as an argument to list.files().
## obtain a list of all the CSV files in directory
theList <- list.files(paste0(getwd(),"/",directory))
Another approach is to combine ./ with the directory argument.
theList <- list.files(paste0("./",directory))
Did I unzip specdata correctly?
Students are given instructions to download the data file required for the assignment, specdata.zip and unzip it in the current R working directory. The zip file contains a directory, and the unzip process creates the directory and stores 332 pollution sensor data files in the subdirectory.
We can confirm the current R directory and whether specdata is a subdirectory from the working directory as follows.
# first, get working directory
getwd()
# second, confirm specdata is a subdirectory of this directory
dir.exists("./specdata")
...and the output:
> # first, get working directory
> getwd()
[1] "/Users/lgreski/gitrepos/datascience"
> # second, confirm specdata is a subdirectory of this directory
> dir.exists("./specdata")
[1] TRUE
>