plot3.R

# Generate a line graph for Date/Time vs Energy sub metering and store in plot3.png

# Read 'household_power_consumption.txt' file
data<-read.table("household_power_consumption.txt", sep=";", header=TRUE, stringsAsFactors=FALSE, nrows=1000000,
                 na.strings = "?")

# Convert to Date to Date type
data$Date<- as.Date(data$Date,format="%d/%m/%Y")

# Subset required data ie data from the dates 2007-02-01 and 2007-02-02
sub <- subset(data, data$Date==as.Date("2007-02-01","%Y-%m-%d")|data$Date==as.Date("2007-02-02","%Y-%m-%d"))

# Remove read data from memory as its no longer required
rm(data)

# Create a DateTime column which stores concantenated Date and Time
sub$DateTime <- strptime(paste(sub$Date,sub$Time), format="%Y-%m-%d %H:%M:%S")

# Open a PNG Graphics Device with width=480 px and height=480 px and file name plot3.png
png("plot3.png", width=480, height=480)

# Plot a line graph for Date/Time vs Energy sub metering for Sub_metering_1
plot(sub$DateTime, sub$Sub_metering_1,
     type="l",                                      # plot lines
     xlab="",                                       # X label
     ylab="Energy sub metering")                    # Y label
lines(sub$DateTime, sub$Sub_metering_2, col="red")  # line graph for Sub_metering_2 with red line color
lines(sub$DateTime, sub$Sub_metering_3, col="blue") # line graph for Sub_metering_3 with blue line color

# Legend at top right for all lines in graph
legend("topright", 
       lty=1,
       col=c("black","red","blue"),
       legend=c("Sub_metering_1","Sub_metering_2","Sub_metering_3"))

# Shutdown graphics device
dev.off()