plot4.R

# Please make sure that the "Read_Data.R" file is also in your R working repository
source('Read_Data.R')

png('plot4.png')
par(mfcol=c(2,2),pty='m')

#---- Draw Top Left plot ------------------------------------

with(dat, plot(DateTime,Global_active_power, type="l",
     xlab="",ylab="Global Active Power"))

#---- Draw Lower Left plot ------------------------------------

with(dat,  plot(DateTime,Sub_metering_1, type="l", col="black", xlab="",ylab="Energy sub metering"))
with(dat,points(DateTime,Sub_metering_2, type="l", col="red"))
with(dat,points(DateTime,Sub_metering_3, type="l", col="blue"))
legend('topright',lty='solid',col=c('black','red','blue'), bty='n',
       legend=c('Sub_metering_1','Sub_metering_2','Sub_metering_3'))

#---- Draw Top Right plot ------------------------------------

with(dat, plot(DateTime,Voltage, type="l",
               xlab="datetime",ylab="Voltage"))

#---- Draw Lower Right plot ------------------------------------

with(dat, plot(DateTime,Global_reactive_power, type="l",
               xlab="datetime",ylab="Global_reactive_power"))

dev.off()