plot4.R

# download data file
if (!file.exists("household_power_consumption.zip"))
{
  download.file(
    url="https://d396qusza40orc.cloudfront.net/exdata%2Fdata%2Fhousehold_power_consumption.zip",
    destfile="household_power_consumption.zip"
  )
}
#read in data file
household_power_consumption <- read.csv(
  unz(description="household_power_consumption.zip", filename="household_power_consumption.txt"), 
  sep=";", 
  na.strings="?")

#format dates
household_power_consumption$Date <-as.Date(household_power_consumption$Date, format="%d/%m/%Y")

#subset to only the two days
days <- c(as.Date("2007-02-01"), as.Date("2007-02-02"))



household_power_consumption <- subset(household_power_consumption,
                                      household_power_consumption$Date %in% days)
#add DateTime column for X axis
household_power_consumption$DateTime <- as.POSIXlt(paste(strftime(household_power_consumption$Date, format="%Y-%m-%d"), household_power_consumption$Time))


# create png file
png(filename = "plot4.png",
    width = 480, height = 480)

par(mfcol=c(2, 2))

#graph 1- same as plot2.png
plot(household_power_consumption$DateTime
     , household_power_consumption$Global_active_power,
     xlab="", ylab="Global Active Power (kilowatts)", type="n"
)
lines(household_power_consumption$DateTime , household_power_consumption$Global_active_power)


#graph 2- same as plot3.png
plot(household_power_consumption$DateTime, household_power_consumption$Sub_metering_1, type="n", xlab="", ylab="Energy sub metering")
lines(household_power_consumption$DateTime, household_power_consumption$Sub_metering_1, col="black")
lines(household_power_consumption$DateTime, household_power_consumption$Sub_metering_2, col="red")
lines(household_power_consumption$DateTime, household_power_consumption$Sub_metering_3, col="blue")
legend("topright", c("Sub_metering_1", legend="Sub_metering_2", "Sub_metering_3"), col=c("black", "red", "blue"), lty = c(1,1))

# graph 3
plot(household_power_consumption$DateTime, household_power_consumption$Voltage, xlab="datetime", ylab="Voltage" ,type="n")
lines(household_power_consumption$DateTime, household_power_consumption$Voltage)

# graph 4
plot(household_power_consumption$DateTime, household_power_consumption$Global_reactive_power, xlab="datetime", ylab="Global_reactive_power" ,type="n")
lines(household_power_consumption$DateTime, household_power_consumption$Global_reactive_power)

dev.off()