gistfile1.txt

pollutantmean <- function(directory, pollutant, id = 1:332) {
        data.files <- list.files(directory, full.names = T)
          alldata <- data.frame()
            for(i in 1:332) {
              alldata <- rbind(alldata, read.csv(data.files[i]))            
  }
          datasubset <- subset(alldata[,"sulfate"] == pollutant && alldata[,"nitrate"] == pollutant && alldata[,"ID"] = id )
          mean(datasubset$pollutant, na.rm = T)
  
}