plot1.R

## This file is the solution for Course Proj 1

## Read the data content at dates 1 and 2/2/2007

# Use regular expression to search for the dates
# at the beginning of each line (^) 
# and output the text (value = TRUE)
f <- readLines("household_power_consumption.txt")
dayMatch <- grep("^[1,2]/2/2007", f, value = TRUE)

# Combine the text with col names, set sep and na.string
# also set colClasses and nrows for efficient read
data <- read.table(text = c(f[1],dayMatch),
                   header = TRUE,             
                   sep = ";",
                   na.strings = "?",
                   colClasses = c(rep("character", 2), rep("numeric", 7)),
                   nrows = length(dayMatch)+1)
data$Date <- as.Date(data$Date, "%d/%m/%Y")

# Plot 1
png(filename = "plot1.png",
    width = 480, height = 480, units = "px")
with(data, hist(Global_active_power, 
                col = "red", 
                main = "Global Active Power",
                xlab = "Global Active Power (kilowatts)"))
dev.off()