plot4.R

# Read in the Electric power consumption data
power <- read.table('household_power_consumption.txt', sep = ';', header = TRUE)

# Subset the data to the dates 2007-02-01 and 2007-02-02
power <- power[power$Date %in% c('1/2/2007', '2/2/2007'), ]

# Convert the Date and Time variables to a Date.Time POSIXlt class variable
power$Time <- paste(power$Date, power$Time, sep = ' ')
power$Time <- strptime(power$Time, format = '%d/%m/%Y %H:%M:%S')
power <- power[, 2:dim(power)[2]]
colnames(power)[1] <- 'Date.Time'

# Convert the data to numeric
power$Global_active_power <- as.numeric(as.character(power$Global_active_power))
power$Voltage <- as.numeric(as.character(power$Voltage))
power$Sub_metering_1 <- as.numeric(as.character(power$Sub_metering_1))
power$Sub_metering_2 <- as.numeric(as.character(power$Sub_metering_2))
power$Sub_metering_3 <- as.numeric(as.character(power$Sub_metering_3))
power$Global_reactive_power <- as.numeric(as.character(power$Global_reactive_power))

# Plot the Global active power, Voltage, Energy sub metering and Global reactive power
# as a function of the date in 4 graphs

png('plot4.png', width = 480, height = 480)
par(mfrow = c(2, 2))

# Plot of Global active power
plot(power$Date.Time, power$Global_active_power, type = 'l', ann = FALSE)
title(ylab = 'Global Active Power (kilowatts)')

# Plot of Voltage
plot(power$Date.Time, power$Voltage, type = 'l', ann = FALSE)
title(xlab = 'datetime', ylab = 'Voltage')

# Plot of Energy sub metering
plot(power$Date.Time, power$Sub_metering_1, type = 'l', ann = FALSE)
lines(power$Date.Time, power$Sub_metering_2, type = 'l', col = 'red')
lines(power$Date.Time, power$Sub_metering_3, type = 'l', col = 'blue')
title(ylab = 'Energy sub metering')
legend('topright', legend = c('Sub_metering_1', 'Sub_metering_2', 'Sub_metering_3'), 
       col = c('black', 'red', 'blue'), lty = c(1, 1, 1))

# Plot of Global reactive power
plot(power$Date.Time, power$Global_reactive_power, type = 'l', ann = FALSE)
title(xlab = 'datetime', ylab = 'Global_reactive_power')
dev.off()