plot4.R

## Multiple plots 

# read data (please save file household_power_consumption.txt in "./data")
 data <- read.csv("./data/household_power_consumption.txt", sep=";", stringsAsFactors=FALSE)

#what is the memory size used by data? 
object.size(data)

#filter data by date and save it in new data frame df
df<-data[data$Date=="1/2/2007"|data$Date=="2/2/2007",]

#what is the memory size used by df?
object.size(df)

#remove the object data to free memory
rm(data)

# Concatenate Date and Time and convert the resulting vector DT to class "POSIXlt"
df$DT<-strptime(paste(df$Date, df$Time, sep=" "), format = "%d/%m/%Y %H:%M:%S")

#My locale is non-english therefore I set LC_TIME for US
Sys.setlocale("LC_TIME", "US")

#plot graphic and save it in png-file
png(filename="plot4.png")
par(mfrow=c(2,2))
with(df,{
     plot(DT,as.numeric(Global_active_power), type="l", xlab="", ylab="Global active power")
     plot(DT,as.numeric(Voltage), type="l", xlab="datetime", ylab="Voltage" )
     plot(DT,as.numeric(Sub_metering_1), type="l", xlab="", ylab="Energy sub metering" )
     legend("topright", lty=1, col=c("black","red", "blue"),legend=c("Sub_metering_1","Sub_metering_2","Sub_metering_3"), bty='n')
     lines(DT,as.numeric(Sub_metering_2), type="l", col="red")
     lines(DT,as.numeric(Sub_metering_3), type="l", col="blue")
     plot(DT,as.numeric(Global_reactive_power), type="l", xlab="datetime", ylab="Global_reactive_power" )
})
dev.off()

#restore my locale
Sys.setlocale("LC_TIME", "")