plot4.R

##############################################################################
# 
# 1. This is a standalone file to produce Plot 4 from Assignment 1
# 2. The steps are as follows:
#         - Step 1. Download raw zipped data from the web if it has not been 
#                   downloaded yet
#         - Step 2. Reading data into data.frame (as part of assignment)
#         - Step 3. Converting Date/Time columns to POSIXt class
#         - Step 4. Subsetting to 2007-02-01:2007-02-02
#         - Step 5. Making plot on screen
#         - Step 6. Exporting to png
#         (Steps 1-4 are the same for all plots; only 5-6 differ)
# 3. The code was run on:
#          OS: UBUNTU 12.04.4 x64
#         IDE: RStudio 0.98.953
#           R: 3.1.1
#
##############################################################################

# Step 1. Download raw zipped data from the web if it has not been downloaded yet

if (!file.exists("tmP.zip")) {
        url <- "https://d396qusza40orc.cloudfront.net/exdata%2Fdata%2Fhousehold_power_consumption.zip"
        download.file(url = url,
                      destfile = "tmP.zip",
                      method = "curl")
        dateDownloaded <- Sys.time()
}
dateDownloaded

# Step 2. Reading data into data.frame (as part of assignment)

con <- unz("tmP.zip", "household_power_consumption.txt")
powerConsumption <- read.table(file = con,
                               header = T,
                               sep = ";",
                               stringsAsFactors = F,
                               na.strings = "?")

# Step 3. Converting Date/Time columns to POSIXt class

powerConsumption$DateTime <- paste(powerConsumption$Date, powerConsumption$Time)
head(powerConsumption$Date)
powerConsumption$DateTime <- strptime(powerConsumption$DateTime, 
                                      "%d/%m/%Y %H:%M:%S",
                                      tz = "GMT")


# Step 4. Subsetting to 2007-02-01:2007-02-02

begin <- as.POSIXlt("2007-02-01", "%Y-%m-%d", tz = "GMT")
end <- as.POSIXlt("2007-02-03", "%Y-%m-%d", tz = "GMT")
plottingDataSubset <- powerConsumption[powerConsumption$DateTime >= begin & powerConsumption$DateTime < end, ]

# Step 5. Make plot 4 on screen
par(mfrow=c(2,2))
with(plottingDataSubset, {
        #plot1
        plot(x=DateTime,
             y=Global_active_power,
             type="l",
             xlab="",
             ylab="Global Active Power")
        #plot2
        plot(x=DateTime,
             y=Voltage,
             type="l",
             xlab="datetime",
             ylab="Voltage")
        #plot3
        plot(x = DateTime,
             y = Sub_metering_1,
             type="n",
             xlab="",
             ylab="Energy sub metering")
        
        lines(x=DateTime,
              y=Sub_metering_1,
              col="black")
        
        lines(x=DateTime,
              y=Sub_metering_2,
              col="red")
        
        lines(x=DateTime,
              y=Sub_metering_3,
              col="blue")
        
        legend("topright",
               bty="n",
               lwd=1, 
               col = c("black", "red", "blue"), 
               legend = c("Sub_metering_1", "Sub_metering_2", "Sub_metering_3"),
               cex=0.5)
        #plot4
        plot(x=DateTime,
             y=Global_reactive_power,
             type="l",
             xlab="datetime",
             ylab="Global_reactive_power")
        
})


# Step 6. Export to png
dev.copy(png,
         file = "plot4.png",
         height = 480,
         width = 480,
         unit = "px")
dev.off()

# END