corr.R

corr <- function(directory, threshold = 0) {
        ## 'directory' is a character vector of length 1 indicating
        ## the location of the CSV files

        ## 'threshold' is a numeric vector of length 1 indicating the
        ## number of completely observed observations (on all
        ## variables) required to compute the correlation between
        ## nitrate and sulfate; the default is 0

        ## Return a numeric vector of correlations
       comp.data <- complete(directory)
       k <- subset(comp.data, comp.data$nobs > threshold)
       obj.id <-c(k[,1])
       L<-length(obj.id)
     j<- vector("numeric", length = 0)
       for (i in obj.id) {
       	raw.data <- getmonitor(i, directory)
       	a <- na.omit(raw.data)
       	b <- cor(a$sulfate, a$nitrate)
        j <- append(j, b, after= length(j))
       }
      c(j)
      j
    }