plot4.R

# creates plot4.png file 480*480 pixels
# 

# read data
power <- read.table("data\\household_power_consumption.txt", header=TRUE, sep=";", as.is = TRUE)

# filter and transform
power12 <- power[power$Date == "1/2/2007" | power$Date == "2/2/2007", ]
power12 <- transform(power12,
                     Global_active_power = as.numeric(Global_active_power),
                     Global_reactive_power = as.numeric(Global_reactive_power),
                     Voltage = as.numeric(Voltage),
                     Sub_metering_1 = as.numeric(Sub_metering_1), 
                     Sub_metering_2 = as.numeric(Sub_metering_2),
                     Sub_metering_3 = as.numeric(Sub_metering_3),
                     datetime = strptime(paste(Date, Time), "%d/%m/%Y %H:%M:%S")
                    )

# global settings for plot
par(mfrow = c(2, 2), mar = c(4,4,2,1))

# plotting
with(power12, 
     {
        plot(datetime, Global_active_power, type = "l", main = NULL, xlab = "",
                ylab = "Global Active Power (kilowatts)")

        plot(datetime, Voltage, type = "l", main = NULL)

        plot(datetime, Sub_metering_1, type = "l", main = NULL, xlab = "", 
                ylab = "Energy Sub Metering")
        lines(datetime, Sub_metering_2, col = "Red")
        lines(datetime, Sub_metering_3, col = "Blue")
        legend("topright", lty = 1, bty = "n", col = c("black", "blue", "red"), inset = c(.24, 0),
                legend = c("Sub_metering_1", "Sub_metering_2", "Sub_metering_3"))

        plot(datetime, Global_reactive_power, type = "l", main = NULL)
     })

# copy to png file
dev.copy(png, file = "plot4.png", width = 480, height = 480)  
dev.off()