Plot4.R

plot4 <- function() {

  ## read data
  powerdata <- read.table("test1/household_power_consumption.txt", stringsAsFactors = FALSE, header = TRUE, sep =";"  )
  
  ## Create column in table with date and time merged together
  FullTimeDate <- strptime(paste(powerdata$Date, powerdata$Time, sep=" "), "%d/%m/%Y %H:%M:%S")
  powerdata <- cbind(powerdata, FullTimeDate)
  
  ## change class of all columns to correct class
  powerdata$Date <- as.Date(powerdata$Date, format="%d/%m/%Y")
  powerdata$Time <- format(powerdata$Time, format="%H:%M:%S")
  powerdata$Global_active_power <- as.numeric(powerdata$Global_active_power)
  powerdata$Global_reactive_power <- as.numeric(powerdata$Global_reactive_power)
  powerdata$Voltage <- as.numeric(powerdata$Voltage)
  powerdata$Global_intensity <- as.numeric(powerdata$Global_intensity)
  powerdata$Sub_metering_1 <- as.numeric(powerdata$Sub_metering_1)
  powerdata$Sub_metering_2 <- as.numeric(powerdata$Sub_metering_2)
  powerdata$Sub_metering_3 <- as.numeric(powerdata$Sub_metering_3)
  
  ## subset data from 2007-02-01 and 2007-02-02
  subsetdata <- subset(powerdata, Date == "2007-02-01" | Date =="2007-02-02")
  
  ## plot the 4 graphs
  png("plot4.png", width=480, height=480)
  par(mfrow=c(2,2))
  with(subsetdata, plot(FullTimeDate, Global_active_power, type="l", xlab="", ylab="Global Active Power"))
  with(subsetdata, plot(FullTimeDate, Voltage, type = "l", xlab="datetime", ylab="Voltage"))
  with(subsetdata, plot(FullTimeDate, Sub_metering_1, type="l", xlab="", ylab="Energy sub metering"))
  lines(subsetdata$FullTimeDate, subsetdata$Sub_metering_2,type="l", col= "red")
  lines(subsetdata$FullTimeDate, subsetdata$Sub_metering_3,type="l", col= "blue")
  legend(c("topright"), c("Sub_metering_1", "Sub_metering_2", "Sub_metering_3"), lty= 1, lwd=2, col = c("black", "red", "blue"))
  with(subsetdata, plot(FullTimeDate, Global_reactive_power, type="l", xlab="datetime", ylab="Global_reactive_power"))
  dev.off()
}