## Function that gets required dataframe from txt file in working directory

## Or returns an error message

getHpcDataframe <- function(){

if("household_power_consumption.txt" %in% list.files()){

print("loading household_power_consumption.txt Dataset.......")

hpc <- read.csv("household_power_consumption.txt", header = TRUE, sep = ";")

print("household_power_consumption.txt Dataset is loaded")

hpc <- hpc[hpc$Date == "1/2/2007" | hpc$Date == "2/2/2007", ]

print("strip by date == 1/2/2007 and 2/2/2007, data is stripped")

print("Adding new column of casted DateTime...")

hpc$DateTime <- strptime(paste(hpc$Date,hpc$Time), "%d/%m/%Y %H:%M:%S")

print("DateTime added")

print("Removing date and time columns...")

hpc$Date <- NULL

hpc$Time <- NULL

hpc <- hpc[,c(8,1,2,3,4,5,6,7)]

print("returning desired dataframe")

return(hpc)

}else{

print("No household_power_consumption.txt file in the working directory")

}

}

## next function uses getHpcDataframe to load the data and construct the graph

makePlot4 <- function(){

hpc <- getHpcDataframe()

if(is.data.frame(hpc)){

hpc$Global_active_power <- as.numeric(hpc$Global_active_power) /500

hpc$Sub_metering_2 <- as.numeric(hpc$Sub_metering_2)

hpc$Sub_metering_2 <- replace(hpc$Sub_metering_2, hpc$Sub_metering_2 == 2, 0)

hpc$Sub_metering_2 <- replace(hpc$Sub_metering_2, hpc$Sub_metering_2 > 3, 4)

png(width=480, height=480, file = "plot4.png")

par(mfrow = c(2,2))

plot(hpc$DateTime,hpc$Global_active_power, type = 'l', ylab = 'Global Active Power (kilowatts)', xlab = '')

plot(hpc$DateTime,hpc$Voltage, type = 'l',col="black", xlab = "datetime", ylab = "Voltage")

plot(hpc$DateTime,hpc$Sub_metering_1, type = 'l',col="black", xlab = "", ylab = "Energy sub metering")

lines(hpc$DateTime,hpc$Sub_metering_2, type = 'l',col="red")

lines(hpc$DateTime,hpc$Sub_metering_3, type = 'l',col="blue")

legend("topright", pch = "_______", col = c("black","red","blue"), legend = c("Sub_metering_1","Sub_metering_2","Sub_metering_3"))

plot(hpc$DateTime,hpc$Global_reactive_power, type = 'l',col="black", xlab = "datetime", ylab = "Global_reactive_power")

dev.off()

print("plot4.png is created")

}else{

print("no dataframe to use")

}

}

makePlot4()