plot4.R

# load data 
data <- read.table("household_power_consumption.txt", header=TRUE, sep=";", na.strings="?")

# filter data
shortdata <- subset(data,as.Date(data$Date,format="%d/%m/%Y") >= as.Date("2007-02-01")  & as.Date(data$Date,format="%d/%m/%Y") <= as.Date("2007-02-02")) 


# draw histogram
png(filename="plot4.png",width=480,height=480,units="px")
par(mfrow = c(2, 2), mar = c(4, 4, 2, 1), oma = c(0, 0, 2, 0))

#plot 1
plot(strptime(as.character(paste(shortdata$Date,shortdata$Time)), format="%d/%m/%Y %H:%M:%S"),shortdata$Global_active_power, type="l",xlab="",ylab="Global Active Power")
#plot 2
plot(strptime(as.character(paste(shortdata$Date,shortdata$Time)), format="%d/%m/%Y %H:%M:%S"),shortdata$Voltage, type="l",xlab="datetime",ylab="Voltage")
#plot 3
plot(strptime(as.character(paste(shortdata$Date,shortdata$Time)), format="%d/%m/%Y %H:%M:%S"),shortdata$Sub_metering_1, type="l",xlab="",ylab="Energy sub metering")
lines(strptime(as.character(paste(shortdata$Date,shortdata$Time)), format="%d/%m/%Y %H:%M:%S"),shortdata$Sub_metering_2,col="red")
lines(strptime(as.character(paste(shortdata$Date,shortdata$Time)), format="%d/%m/%Y %H:%M:%S"),shortdata$Sub_metering_3,col="blue")
legend("topright", "(x,y)",c("Sub_metering_1", "Sub_metering_2","Sub_metering_3"),  lty=1, col = c("black","blue","red"))
#plot 4
plot(strptime(as.character(paste(shortdata$Date,shortdata$Time)), format="%d/%m/%Y %H:%M:%S"),shortdata$Global_reactive_power, type="l",xlab="datetime",ylab="global_reactive_power")


dev.off()