pollutantmean.R

pollutantmean <- function(directory, pollutant, id = 1:332) {
  
    ## 'directory' is a character vector of length 1 indicating
    ## the location of the CSV files
    
    ## 'pollutant' is a character vector of length 1 indicating
    ## the name of the pollutant for which we will calculate the
    ## mean; either "sulfate" or "nitrate".
    
    ## 'id' is an integer vector indicating the monitor ID numbers
    ## to be used
    
    ## Returns the mean of the pollutant across all monitors list
    ## in the 'id' vector (ignoring NA values)
    
    files <- (Sys.glob("specdata//*.csv"))[id];
    
    combined_data <- c()
    
    for (file in files) {
        file_data <- read.csv(file, sep = ",");
        pollutant_data <- file_data[,pollutant];
        pollutant_data <- pollutant_data[!is.na(pollutant_data)]
        combined_data <- c(combined_data, pollutant_data)
    }
    
    return(mean(combined_data));
}