## plot3.png

## Below is just reference URL if needed for later; data file is now in my working directory.

## fileUrl <- "https://d396qusza40orc.cloudfront.net/exdata%2Fdata%2Fhousehold_power_consumption.zip"

## download.file(fileUrl, destfile = "./household_power_consumption.txt", method = "curl")

## Apply TA Astrego's suggestion on forum to use skip/nrows to grab only data for 2/1/2007

## and 2/2/2007, and add in column names afterward.

## First I calculated the number of rows to be skipped as:

## 1(header)+396(12/16/2006 instances)+66240(12/17/2006-1/31/2007 instances)=66637 rows

## I calculated we must then read (60min/hr)*(24hr/day)*(2days)=2880 rows for 2/1/2007-2/2/2007.

## I then added header row names with col.names in read.table below.

hpcData <- read.table("./household_power_consumption.txt", header=FALSE,

sep=";", fill=FALSE, strip.white=TRUE,stringsAsFactors=FALSE,

na.strings="?", skip=66637, nrows=2880,

col.names=c("Date","Time","Global_active_power","Global_reactive_power",

"Voltage","Global_intensity","Sub_metering_1","Sub_metering_2",

"Sub_metering_3"))

## Grab only rows that do not have missing values

data <- hpcData[complete.cases(hpcData), ]

## Change Date column format

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

## Add column indicating abbreviated weekday

data$Weekday <- weekdays(data$Date, abbreviate=TRUE)

## Merge date and time

datestring <- paste(as.character(data$Date),data$Time)

data$DateTime <- strptime(datestring, "%Y-%m-%d %H:%M:%S")

## Make plot3.png

png(file = "plot3.png") ## Open PNG device; create 'plot3.png' in my working directory

## Create plot and send to a file (no plot appears on screen)

par(mar=c(4,4,2,1)) ## Set plot margins

plot(data$DateTime,data$Sub_metering_1, main=NULL,

xlab='', ylab="Energy sub metering", type="n")

lines(data$DateTime,data$Sub_metering_1, type="l",col="black")

lines(data$DateTime,data$Sub_metering_2, type="l",col="red")

lines(data$DateTime,data$Sub_metering_3, type="l",col="blue")

legend("topright",lty=1, lwd=2, col=c("black","red","blue"),

legend=c("Sub_metering_1","Sub_metering_2","Sub_metering_3"))

dev.off() ## Close the PNG file device