plot2.R

library(tibble)

## Checking if code was run before
if (file.exists("extrData.txt")) {
        extrData <- read.table("extrData.txt", header = T, sep = ";")
} else {
## Downloading and unzipping file if it does not exist
        if (!file.exists("household_power_consumption.zip") & 
        !file.exists("household_power_consumption.txt")) {
        myURL <- "https://d396qusza40orc.cloudfront.net/exdata%2Fdata%2Fhousehold_power_consumption.zip"
        download.file(myURL, destfile = "household_power_consumption.zip")
        unzip("household_power_consumption.zip")
        }

## Reading data
data <- read.table("household_power_consumption.txt", sep = ";", header = T,
                   na.strings = "?")
## Subseting required dates and removing stored data
extrData <- subset(data, data$Date == "1/2/2007" | data$Date == "2/2/2007")
rm(list = "data")

## Writing new table
write.table(extrData, file = "extrData.txt", row.names = F, sep = ";")
}

## Adding  date with time column
Date_Time <- paste(extrData$Date, extrData$Time, sep = " ") %>% 
        strptime(format = "%d/%m/%Y %H:%M:%S")
extrData <- add_column(extrData, Date_Time = Date_Time)
rm(list = "Date_Time")

## writing to png file "plot2.png"
png(file="plot2.png", width=480, height=480)
plot(extrData$Date_Time, extrData$Global_active_power, xlab = "", 
     ylab = "Energy sub metering", type = "l")
dev.off()