plot4.R

# read data file
consumption <- read.csv("household_power_consumption.txt", sep=";", stringsAsFactors = F)

# subset for dates 01-02-2007 and 02-02-2007
consumption <- subset(consumption, consumption$Date  == "1/2/2007" | consumption$Date  == "2/2/2007")

# create new field joining date & time
consumption$datetime <- strptime(paste(consumption$Date, consumption$Time, sep=" "), "%d/%m/%Y %H:%M:%S")

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

# Draw plot in png file
par(mfrow = c(2,2), mar=c(6, 4, 3, 2)) 
# plot 1, 1
with(consumption, plot(consumption$datetime, as.numeric(consumption$Global_active_power ), type="n", ylab="Global Active Power", xlab=""))
lines(consumption$datetime, as.numeric(consumption$Global_active_power))

# plot 1, 2
with(consumption, plot(consumption$datetime, as.numeric(consumption$Voltage ), type="n", ylab="Voltage", xlab="datetime"))
lines(consumption$datetime, as.numeric(consumption$Voltage))

par(mar=c(5, 4, 3, 2)) 

# plot 2, 1
with(consumption, plot(consumption$datetime, as.numeric(consumption$Sub_metering_1 ), type="n", ylab="Energy sub metering", xlab=""))
lines(consumption$datetime, as.numeric(consumption$Sub_metering_1), col="black")
lines(consumption$datetime, as.numeric(consumption$Sub_metering_2), col="red")
lines(consumption$datetime, as.numeric(consumption$Sub_metering_3), col="blue")
legend("topright", lty=c(1,1), col = c("black", "red", "blue"), legend= c("Sub_metering_1", "Sub_metering_2", "Sub_metering_3"), bty = "n")

# plot 2, 2
with(consumption, plot(consumption$datetime, as.numeric(consumption$Global_reactive_power ), type="n", ylab="Global_reactive_power", xlab="datetime"))
lines(consumption$datetime, as.numeric(consumption$Global_reactive_power))

# close file
dev.off()