plot4.R

## Read data

url <- "https://d396qusza40orc.cloudfront.net/exdata%2Fdata%2Fhousehold_power_consumption.zip"
temp <- tempfile()
download.file(url,temp)
data <- read.table(unz(temp, "household_power_consumption.txt"),sep = ";", header = TRUE)
unlink(temp)

## Subset data based on desired dates

data$Date <- as.Date(data$Date,"%d/%m/%Y")
data <- data[data$Date >= "2007/02/01" & data$Date <= "2007/02/02",]

## Create a PosixLT value and add it to the data

data <- tidyr::unite(data, DateTime, Date, Time, sep = ' ', na.rm = TRUE, remove = FALSE) 

## Coerce Datetime and Numeric Data to the right class

data$DateTime <- with(data, as.POSIXct(DateTime, format = "%Y-%m-%d %H:%M:%OS"))
data[,4:10] <- sapply(data[,4:10],as.numeric)

## GRAPH 4
png(file="./plot4.png", width=480, height=480)

par(mfrow = c(2, 2))
with(data, {
        plot(DateTime, Global_active_power, type = "l", ylab = "Global Active Power", xlab = "")
        plot(DateTime, Voltage, type = "l", xlab = "datetime")
        plot(DateTime, Sub_metering_1, type = "l", ylab = "Energy Sub Metering", xlab = "")
        lines(data$DateTime, data$Sub_metering_2, col="red")
        lines(data$DateTime, data$Sub_metering_3, col="blue")
        legend("topright", lty = 1, col = c("black", "red", "blue"), 
               legend = c("Sub_Metering_1", "Sub_Metering_2", "Sub_Metering_3"))
        plot(DateTime, Global_reactive_power, type = "l")
        })

dev.off()