Coursera course - R Programming week two practical assignment part 3

This assignment requires use of the cor() function to get sulfate/nitrate correlations for files which have at least the threshold number of rows with complete data. My solution is below. Note that the test data given on the website is given to 5 decimal places for the head() cases but to only four decimal places for the summary() cases. I have kept all results accurate to 5 decimal places so there are some differences between my summary cases and those given on the Coursera site.

cr <- function(threshold=0){
  filenames <- paste(sprintf("%03d",1:332),".csv",sep="")
  result <- numeric(0)
  for (file in filenames){
    tmp <- read.csv(file, header=TRUE)
    tmp$Date <- NULL
    tmp$ID <- NULL
    tmp <- tmp[complete.cases(tmp),]
    if(nrow(tmp) >= threshold){
      res <- cor(tmp$sulfate,tmp$nitrate)
      res <- round(res, digits = 5)
      result <- append(result,res)
      rm(res)
    }   
    rm(tmp)  
  } 
  return(result)
}

Test Output:

> wa <- cr(150)
> head(wa)
[1] -0.01896 -0.14051 -0.04390 -0.06816 -0.12351 -0.07589
> summary(wa)
    Min.  1st Qu.   Median     Mean  3rd Qu.     Max. 
-0.21060 -0.05146  0.09333  0.12400  0.26840  0.76310 
> wb <- cr(400)
> head(wb)
[1] -0.01896 -0.04390 -0.06816 -0.07589  0.76313 -0.15783
> summary(wb)
    Min.  1st Qu.   Median     Mean  3rd Qu.     Max. 
-0.17620 -0.03109  0.10020  0.13970  0.26850  0.76310 
> qa <- cr(5000)
> summary(qa)
   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
                                                
> length(qa)
[1] 0
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