plot3.R

## Read the data file, account for na, set decimal point and header
household_power_consumption <- read.table('data/household_power_consumption.txt',
                                header=TRUE, dec=".", sep=";", na.strings = "?")
## Convert the Date column to date format
household_power_consumption$Date <-  as.Date(household_power_consumption$Date, 
                                             format="%d/%m/%Y")

## subset the dataset to two days of interest
data <- subset(household_power_consumption,  
               Date == as.Date('2007-02-01') | Date == as.Date('2007-02-02'))

# get the range for the x and y axis
xrange <- c(1,length(data$Date))
yrange <- range(data$Sub_metering_1) 

# set up the plot
plot3 <- plot(xrange, yrange, type="n", xlab="",
     ylab="Energy sub metering", xaxt="n") 
lines(data$Sub_metering_1) 
lines(data$Sub_metering_2, col="red") 
lines(data$Sub_metering_3, col="blue") 
axis(1, at=c(0,1440,2880), labels=c("Thu", "Fri", "Sat"))
legend("topright", c("Sub_metering_1", "Sub_metering_2", "Sub_metering_3"), cex=0.6, col=c("black", "red", "blue"),
       lty=c(1, 1, 1))


## copy my plot to a PNG file
dev.copy(png, file="plot3.png", width=480, height=480)

## close PNG device
dev.off()