#Assigment 2

getwd()

setwd("C:/Users/aurquhart/Documents/Github/R_Programming_Assignment2")

#Point and download zip

dataset_url <- "https://d396qusza40orc.cloudfront.net/rprog%2Fdata%2Fspecdata.zip"

download.file(dataset_url, "specdata.zip")

#unzip file

unzip("specdata.zip", exdir = "specdata")

#check files

list.files("specdata//specdata")

#So we're going to write a function to calculate the mean of

#a field in the files - sulfate or nitrate

#Step 1 - test the loop to consolodate files

files <- list.files("specdata//specdata")

directory <- "specdata//specdata"

files_list <- list.files(directory, full.names=TRUE) #creates a list of files

dat <- data.frame() #creates an empty data frame

number_of_files <- length(files)

for (i in 1:number_of_files) { #loops through the files, rbinding them together

dat <- rbind(dat, read.csv(files_list[i]))

}

#Now need to test that I can calculate the mean of the 2 fields

mean(dat[, "sulfate"], na.rm=TRUE) #identifies the mean weight

mean(dat[, "nitrate"], na.rm=TRUE) #identifies the mean weight

#head(dat)

#Now put it all into a function

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

## Return the mean of the pollutant across all monitors list

## in the 'id' vector (ignoring NA values)

dat <- data.frame() #creates an empty data frame

files_list <- list.files(directory, full.names=TRUE) #creates a list of files

for (i in id) { #loops through the files, rbinding them together

dat <- rbind(dat, read.csv(files_list[i]))

}

mean(dat[, pollutant], na.rm=TRUE)

}

pollutantmean("specdata","sulfate",id=1:5)