plot4.R

png(filename='plot4.png', height=480, width=480)
par(mfrow=c(2,2), mar=c(4,4,2,1), oma=c(0,0,2,0))
with(dtsub, {
  plot(Global_active_power~as.POSIXct(dtsub$Time), type="l", xlab="", ylab="Global Active Power (kilowatts)")
  plot(Voltage~as.POSIXct(dtsub$Time), type="l", xlab="", ylab="Voltage (volt)")
  plot(Sub_metering_1~as.POSIXct(dtsub$Time), type="l", xlab="", ylab="Global Active Power (kilowatts)")
  lines(Sub_metering_2~as.POSIXct(dtsub$Time),col='Red')
  lines(Sub_metering_3~as.POSIXct(dtsub$Time),col='Blue')
  legend(col=c("black", "red", "blue"), lty=1, lwd=2, bty="n", legend=c("Sub_metering_1", "Sub_metering_2", "Sub_metering_3"), "topright")
  plot(Global_reactive_power~as.POSIXct(dtsub$Time), type="l", xlab="", ylab="Global Rective Power (kilowatts)")
})
dev.off()