plot3.R

## This file is the solution for Course Proj 1

## Read the data content at dates 1 and 2/2/2007

# Use regular expression to search for the dates
# at the beginning of each line (^) 
# and output the text (value = TRUE)
f <- readLines("household_power_consumption.txt")
dayMatch <- grep("^[1,2]/2/2007", f, value = TRUE)

# Combine the text with col names, set sep and na.string
# also set colClasses and nrows for efficient read
data <- read.table(text = c(f[1],dayMatch),
                   header = TRUE,             
                   sep = ";",
                   na.strings = "?",
                   colClasses = c(rep("character", 2), rep("numeric", 7)),
                   nrows = length(dayMatch)+1)
data$Date <- as.Date(data$Date, "%d/%m/%Y")

# Plot 3
png(filename = "plot3.png",
    width = 480, height = 480, units = "px")
yrange <- with(data, range(c(Sub_metering_1,Sub_metering_2,Sub_metering_3)))
with(data, plot(Sub_metering_1, xaxt = "n", ylim = yrange, type = "l", xlab = "", ylab = ""))
par(new=T)
with(data, plot(Sub_metering_2, xaxt = "n", ylim = yrange, type = "l", xlab = "", ylab = "", col = "red"))
par(new=T)
with(data, plot(Sub_metering_3, xaxt = "n", ylim = yrange, type = "l", xlab = "", ylab = "", col = "blue"))
par(new=F)
axis(side = 1, at = c(1,2880/2,2880), 
     labels = c("Thu", "Fri", "Sat"))
title(ylab = "Energy sub metering")
legend("topright", lty = c(1,1,1), lwd = c(2.5, 2.5, 2.5), col = c("black", "blue", "red"),
       legend = c("Sub_metering_1", "Sub_metering_2", "Sub_metering_3"))
dev.off()