plot2.R

#Plot2

#Prepare data for plotting. 
#First, work out what lines to read

line1 <- strptime("2006-12-16 17:24:00", "%Y-%m-%d %H:%M:%S")
dataStart <- strptime("2007-02-01 00:01:00", "%Y-%m-%d %H:%M:%S")
dataStartLine <- as.numeric(dataStart - line1) * 24 * 60 
numLines <- 48 * 60 # total number of rows to read in

#Read in relevant lines of data - assuming working directory contains household_power_consumption.txt
houseData <- read.csv("household_power_consumption.txt", header=FALSE, sep=";", skip=dataStartLine,nrows=numLines)
head(houseData)

#Build on screen
plot.new()
par(mar=c(4,4,2,2), cex.axis=0.8,cex.lab=0.8)
#Column 3 is global active power
plot(houseData$V3, type="l", xaxt = "n", xlab="", ylab="Global Active Power (kilowatts)")
axis(1, at=c(1,numLines/2,numLines), labels=c("Thu", "Fri", "Sat"))

dev.copy(png, file = "plot2.png") ## Copy to png file 
dev.off()