plot3.R

data <- read.csv('household_power_consumption.txt', sep=';',
                 colClasses='character')
data <- data[data$Date %in% c('1/2/2007', '2/2/2007'),]
data <- within(data, {
    Sub_metering_1 <- as.numeric(Sub_metering_1)
    Sub_metering_2 <- as.numeric(Sub_metering_2)
    Sub_metering_3 <- as.numeric(Sub_metering_3)
    t <- strptime(paste(Date, Time), '%d/%m/%Y %H:%M:%S')
})

png(filename = "plot3.png", width = 480, height = 480)
with(data, {
     plot(t, Sub_metering_1, type='l', xlab='',
          ylab='Energy sub metering')
     lines(t, Sub_metering_2, col='red')
     lines(t, Sub_metering_3, col='blue')
     legend('topright', lwd=1, col=c('black', 'red', 'blue'),
            legend=c('Sub_metering_1', 'Sub_metering_2', 'Sub_metering_3'))
})
dev.off()