plot4.r

# Function for loading a smaller interval from a dataset in a CSV.
# The csv must contain columns "Date" and "Time"
# in the following format: %d/%m/%Y and %H:%M:%S
loadIntervalCSV <- function (pathToCsv, firstDay, nDays = 1) {
  # Load first row
  firstRow <- read.csv(pathToCsv, sep=";", nrows=1)
  
  # Epoch of the first record
  epochFirstRow <- as.integer(
    as.POSIXct(paste(firstRow$Date, firstRow$Time), format="%d/%m/%Y %H:%M:%S")
  )
  
  # Epoch of the first minute of a given day
  epochStart <- as.integer(
    as.POSIXct(paste(firstDay, "00:00:00"), format="%d/%m/%Y %H:%M:%S")
  )
  
  # Number of minutes between of the first record to be read i.e. rows to skip
  skipRows = (epochStart - epochFirstRow) / 60
  
  # Number of minutes in n days
  minutes2days = 24 * 60 * nDays
  
  # Load data
  dataSet <- read.csv("household_power_consumption.txt", sep=";", 
                      skip=skipRows, nrows=minutes2days)
  
  # Set colnames in dataSet
  colnames(dataSet) <- colnames(firstRow)

  return(dataSet)
}

# Load 2007-02-01 and 2007-02-02
dataSet <- loadIntervalCSV("household_power_consumption.txt", "01/02/2007", nDays = 2)

# Start device
png(file = "plot4.png")

# Adjust Locale
#Sys.setlocale("LC_TIME", "en_US.utf8")

# Creates a Datetime column in dataset
dataSet$Datetime = as.POSIXct(paste(dataSet$Date, dataSet$Time), 
                              format = "%d/%m/%Y %H:%M:%S"))

# Let plot region to allow 4 graphs and set bg color
par(mfcol = c(2,2), bg = "transparent")

# Plot top-left
with(dataSet, 
  # Draw plot 1
  plot(Global_active_power ~ Datetime, type="l", xlab="",
       ylab="Global Active Power")
)

# Plot bottom-left
with(dataSet, {
  plot(Sub_metering_1 ~ Datetime,
       ylab = "Energy sub metering",
       xlab = "",
       type = "l",
       col  = "black")
  lines(Sub_metering_2 ~ Datetime, col = "red")
  lines(Sub_metering_3 ~ Datetime, col = "blue")
  legend("topright", lty = "solid", col = c("black", "red", "blue"), 
       legend = c("Sub_metering_1", "Sub_metering_2", "Sub_metering_3"),
       box.lwd = 0)
})

# Plot top-right
with(dataSet, {
  plot(Voltage ~ Datetime,
       ylab="Voltage",
       xlab="datetime",
       type="l")
})

# Plot bottom-right
with(dataSet, {
  plot(Global_reactive_power ~ Datetime,
       ylab="Global_reactive_power",
       xlab="datetime",
       type="l")
})


# Close the device
dev.off()