plot2.R

plot2 <- function(){
        ## Aim of this function is to 
        ## 1. read the household_power_consumption.txt file
        ## 2. subset for data taken from 2 days: 2007-02-01 and 2007-02-02
        ## 3. generate a plot of global active power vs. time
        
        ## Parameters: none
        ## Assumes household_power_consumption.txt file located in working dir
        
        ## read data
        powerdata <- read.table("./household_power_consumption.txt", stringsAsFactors = FALSE, header = TRUE, sep =";"  )
        
        ## Create column in table with date and time merged together
        FullTimeDate <- strptime(paste(powerdata$Date, powerdata$Time, sep=" "), "%d/%m/%Y %H:%M:%S")
        powerdata <- cbind(powerdata, FullTimeDate)
        
        ## change class of all columns to correct class
        powerdata$Date <- as.Date(powerdata$Date, format="%d/%m/%Y")
        powerdata$Time <- format(powerdata$Time, format="%H:%M:%S")
        powerdata$Global_active_power <- as.numeric(powerdata$Global_active_power)
        powerdata$Global_reactive_power <- as.numeric(powerdata$Global_reactive_power)
        powerdata$Voltage <- as.numeric(powerdata$Voltage)
        powerdata$Global_intensity <- as.numeric(powerdata$Global_intensity)
        powerdata$Sub_metering_1 <- as.numeric(powerdata$Sub_metering_1)
        powerdata$Sub_metering_2 <- as.numeric(powerdata$Sub_metering_2)
        powerdata$Sub_metering_3 <- as.numeric(powerdata$Sub_metering_3)
        
        ## subset data from 2007-02-01 and 2007-02-02
        subsetdata <- subset(powerdata, Date == "2007-02-01" | Date =="2007-02-02")
        
        ## plot globalactivepower vs date&time
        png("plot2.png", width=480, height=480)
        with(subsetdata, plot(FullTimeDate, Global_active_power, type="l", xlab="Day", ylab="Global Active Power (kilowatts)"))
        dev.off()
}