plot2.R

library(data.table)

# Read the whole dataset into pc_data. 
# Keep only the following two dates, "1/2/2007" and "2/2/2007".
# Convert the Date column to IDate class and Time column to ITime class.
pc_data <- fread("household_power_consumption.txt", sep = ";",
                 na.strings = "?")
pc_data <- subset(pc_data, Date %in% c("1/2/2007", "2/2/2007"))
pc_data[,Date:=as.IDate(Date, format = "%d/%m/%Y")]
pc_data[,Time:=as.ITime(Time, format = "%H:%M:%S")]

# Add DateTime colume that combines Date and Time column. Useful for plotting
pc_data[, DateTime:=as.POSIXct(Time, tz = "UTC", date = Date)]

# Plot "Global_active_power" vs "Datetime" and save to a png file.
png("plot2.png", bg = "transparent")
with(pc_data, 
     plot(DateTime, Global_active_power,
          type = "l", main = "", xlab = "",
          ylab = "Global Active Power (kilowatts)")
)
dev.off()