Week2Assignment1.R

pollutantmean <- function(directory, pollutant, id = 1:332) {
  files <- sprintf("%s/%03d.csv", directory, id)
  measurements <- c()
  for (file in files) {
    frame <- read.csv(file)
    file_measurements <- frame[[pollutant]]
    measurements <- c(measurements, file_measurements)
  }
  mean(measurements, na.rm = TRUE)
}

complete <- function(directory, id = 1:332){
  counts <- data.frame("id","nobs")
  colnames(counts) <- c("id", "nobs")
  for (i in id) {
    file <- sprintf("%s/%03d.csv", directory, i)
    frame <- read.csv(file)
    count <- length(frame[!is.na(frame$sulfate) & !is.na(frame$nitrate),]$ID)
    print(count)
    counts[id,]$id <- id
    counts[id,]$nobs <- count
    ## need to figure out how to append a row to a data frame
  }
  counts
}

corr <- function(directory, threshold = 0) {
  files <- list.files(directory, full.names = TRUE)
  corrs <- c()
  for (file in files) {
    frame <- read.csv(file)
    complete <- frame[!is.na(frame$sulfate) & !is.na(frame$nitrate),]
    count <- length(complete$ID)
    if (count > threshold){
      corrs <- c(corrs, cor(complete$nitrate, complete$sulfate))
    }
  }
  corrs
}