## (there are only two days, so date alone wouldn't produce sufficient data')

## we use a combination of date and time

## first convert character to date ...

data$Date <- strptime(data$Date, "%d/%m/%Y")

## ... then add time to it (using strptime does not work),

## creating a new combination Moments

data$Moments <- as.POSIXct(paste(data$Date, data$Time))

png("plot2.png", width=480, height= 480) # open png device

par(mfrow = c(2,2)) # 2x2 plots, row-wise

# row 1, col 1

plot(data$Moments,

data$Global_active_power,

type= "l",

ylab= "Global Active Power (kilowatts)",

xlab="")

# row 1, col 2

plot(data$Moments,

data$Voltage,

type= "l",

ylab= "Voltage",

xlab="datetime")

# row 2, col 1

plot(data$Moments,

data$Sub_metering_1,

type= "n",

ylab= "Energy sub metering",

xlab="")

points(data$Moments,

data$Sub_metering_1,

type= "l",

col="black")

points(data$Moments,

data$Sub_metering_2,

type= "l",

col="red")

points(data$Moments,

data$Sub_metering_3,

type= "l",

col="blue")

legend("topright",

c("Sub_metering_1","Sub_metering_2","Sub_metering_3"),

lty=c(1,1,1),

lwd=c(2.5,2.5,2.5),

col=c("black","red","blue"))

# row 2, col 2

plot(data$Moments,

data$Global_reactive_power,

type= "l",

ylab= "Global reactive power",

xlab="datetime")

dev.off() ## close device