plot4.R

rawDataFileName <- "../household_power_consumption.txt"

# Read the data from the file.
# For now keep the date and time as a  character strings.
d <- read.table(rawDataFileName,
                header = TRUE,
                sep = ";",
                na.strings = "?",
                colClasses = c("character",
                               "character",
                               "numeric",
                               "numeric",
                               "numeric",
                               "numeric",
                               "numeric",
                               "numeric",
                               "numeric"
                ),
                comment.char = ""
)

# Keep only the needed dates.
# The dates appear to be in the D/M/YYYY format,
# without leading zeros.
d <- subset(d, Date %in% c("1/2/2007", "2/2/2007"))

# Convert the Date and Time character strings to a timestamp.
d$Timestamp <- as.POSIXct(paste(d$Date, d$Time, sep = " "),
                          format = "%d/%m/%Y %H:%M:%S"
)
# Drop the Date and Time character strings.
d <- d[, ! names(d) %in% c("Date", "Time")]

# Open the plot file
png("plot4.png")

# Set up a 2 by 2 matrix for the plots
par(mfcol = c(2, 2))

# Draw the Global_active_power over time.
plot(d$Timestamp, d$Global_active_power,
     type = "l",
     xlab = "",
     ylab = "Global Active Power"
)

# Draw the Sub_metering_[1-3] over time.
plot(d$Timestamp, d$Sub_metering_1,
     type = "l",
     col = "black",
     xlab = "",
     ylab = "Energy sub metering"
)
lines(d$Timestamp, d$Sub_metering_2,
      type = "l",
      col = "red"
)
lines(d$Timestamp, d$Sub_metering_3,
      type = "l",
      col = "blue"
)
legend("topright",
       legend = c("Sub_metering_1", "Sub_metering_2", "Sub_metering_3"),
       col = c("black", "red", "blue"),
       lty = 1,
       bty = "n"
)

# Draw the Voltage over time.
plot(d$Timestamp, d$Voltage,
     type = "l",
     xlab = "datetime",
     ylab = "Voltage"
)

# Draw the Global_reactive_power over time.
plot(d$Timestamp, d$Global_reactive_power,
     type = "l",
     xlab = "datetime",
     ylab = "Global_reactive_power"
)

# Close the plot file.
dev.off()