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Purpose

In the course of partaking an online class regarding data analysis, in particular the class Exploratory Data Analysis, one assignment was a project with the purpose to demonstrate the student's ability to collect, work with, and plot a data set in various ways.

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Introduction

This assignment uses data from the UC Irvine Machine Learning Repository, a popular repository for machine learning datasets. In particular, we will be using the "Individual household electric power consumption Data Set" which have been made available on the [course web site][].

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Assignment

Create a set of R script which carry out the following steps:

1. Load the data;
2. Create four R scripts (plot1.R, plot2.R, plot3.R, plot4.R);
3. Create four plots by facilitating merely the base plotting system, and by executing each of the four aforementioned R scripts correspondingly;
4. Save each of these plots to a corresponding PNG file, each of size 480x480 pixels;
5. Submit the script and the generate PNG files to a GitHub repository.

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Quick start

1. Download the repository files to your local machine;
2. Open the R project file (course project 1.Rproj);
3. Open and run the main R script (plot.R).

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Project

The project comprises several directories and files, all of which are outlined below.

Directory structure

In the project directory you will find several subdirectories.

<project directory>/
  +- course project 1.Rproj
  +- data/
  |    +- exdata%2Fdata%2Fhousehold_power_consumption.zip
  |    +- household_power_consumption.txt
  |    +- reference-plot-1.png
  |    +- reference-plot-2.png
  |    +- reference-plot-3.png
  |    +- reference-plot-4.png
  +- doc/
  +- lib/
  |    +- bldurl.R
  |    +- chkdir.R
  |    +- chkurl.R
  |    +- dldat.R
  |    +- estuciepc.R
  |    +- plot1.R
  |    +- plot2.R
  |    +- plot3.R
  |    +- plot4.R
  |    +- rduciepc.R
  |    +- setusragnt.R
  |    +- sstuciepc.R
  +- plot.R
  +- publishing/
  +- README.md (GitHub compatible)
  +- README.Rmd

The data directory contains the downloaded data file, both as a compressed archive (zip), as well as the uncompress individual data files.

Any additional, supporting scripts or libraries are stored inside the lib directory.

Files

For reasons of readability, testing, profiling, benchmarking and re-usability, instead of creating one single script file, an approach of splitting the script into several functions, each put into a corresponding script file of its own, placed into the lib directory, has been taken.

plot.R

The main entry point, the main script, Upon which execution all required libraries and supporting scripts are getting loaded, as well as global variables and constants are defined.

Steps carried out by this script:

1. check for existence of the doc, data, and publishing directories, and create these if required;
2. download and uncompress data file (raw data) if not already available;
3. estimate the size of main memory required for loading the data set into the memory;
4. load the data set into a data.table dtInDat;
5. extract a subset of data.table dtInDat;
6. create the four plots (plot1.png, plot2.png, plot3.png, and plot4.png) by executing the corresponding scripts (lib/plot1.R, lib/plot2.R, lib/plot3.R, and lib/plot4.R).

lib/bldurl.R

Assemble an URL from individual parts by concatenating these, encode it and/or check it for existance if requested.

Parameter	Description
...	individual components of the URL
encURL	if TRUE, the URL gets encoded after assembly
chkURL	if TRUE, the URL's existance gets verified

Table: Input parameter

Result	Description
TRUE	success; URL has been assembled (and is existing)
FALSE	failure; URL couldn't be assembled (or is not existing)

Table: Output value

lib/chkdir.R

Check whether a specific directory is already existing, and if not create that directory.

Parameter	Description
dname	vector of directory names to check/create
mkdir	create directories if non-existing

Table: Input parameter

Result	Description
TRUE	success; directories are existing/have been created successfully
FALSE	failure; directories are not existing/cannot be created

Table: Output value

lib/chkurl.R

Check whether a specific URL is valid, and if it can be accessed.

Parameter	Description
valURLurl	vector of URLs to check/validate

Table: Input parameter

Result	Description
TRUE	success; vector; URLs are valid and accessible
FALSE	failure: vector; URLs are not existing/cannot be accessed

Table: Output value

lib/dldat.R

Download data into indicated directory, expand if requested, and rename as specified.

Parameter	Description
dlname	vector of files to downloads
dldir	vector of directories files to download to
fname	local filenames of downloaded files
exp	expand downloaded files?
redl	re-download files?

Table: Input parameter

Result	Description
TRUE	success; directory is existing/has been created successfully
FALSE	failure; directory does not exist/cannot be created

Table: Output value

Note
Case #1) dlname, dldir, fname have to be of identical length, -or-
Case #2) dlname and fname have to be of identical length, and dldir has to be of length 1.

lib/estuciepc.R

Estimate the aount of memory required to load and store the read raw data.

Parameter	Description
basedir	base directory to read files from
fname	file to read
unts	unit of size returned ("b", "k", "m", "g")

Table: Input parameter

Result	Description
estimated memory size	success; rough estimate of the memory required to store the raw data
NULL	failure

Table: Output value

Note

• both--baseDir and fname--have to be provided, and set to a non-NULL value;
• "b" = bytes; "k" = kilo bytes, "m" = mega bytes, "g" = giga bytes.

lib/plot1.R

Plot the data provided both to the screen as well as a file (format png) by facilitating the R base plot system only

Plot specification:

• histogram;
• global active power (x-axis);
• frequency (y-axis).

Parameter	Description
dtPlt	data table containing the data to plot
fname	name of the file the plot has to sent to
imgSize	size/dimension (xx) of the plot generated and written to file

Table: Input parameter

Result	Description
TRUE	success; data have been plot both the screen as well as the file
FALSE	failure

Table: Output value

Note
All of dtPlt, fname, and imgSize have to be provided, and set to a non-NULL value.

lib/plot2.R

Plot the data provided both to the screen as well as a file (format png) by facilitating the R base plot system only

Plot specification:

• "time series";
• date & time of day (x-axis);
• global active power (y-axis).

Parameter	Description
dtPlt	data table containing the data to plot
fname	name of the file the plot has to sent to
imgSize	size/dimension (xx) of the plot generated and written to file

Table: Input parameter

Result	Description
TRUE	success; data have been plot both the screen as well as the file
FALSE	failure

Table: Output value

Note
All of dtPlt, fname, and imgSize have to be provided, and set to a non-NULL value.

lib/plot3.R

Plot the data provided both to the screen as well as a file (format png) by facilitating the R base plot system only

Plot specification:

• "time series";
• date & time of day (x-axis);
• sub metering 1, sub metering 2, sub metering 3 (y-axis).

Parameter	Description
dtPlt	data table containing the data to plot
fname	name of the file the plot has to sent to
imgSize	size/dimension (xx) of the plot generated and written to file

Table: Input parameter

Result	Description
TRUE	success; data have been plot both the screen as well as the file
FALSE	failure

Table: Output value

Note
All of dtPlt, fname, and imgSize have to be provided, and set to a non-NULL value.

lib/plot4.R

Plot the data provided both to the screen as well as a file (format png) by facilitating the R base plot system only

Plot specification:

• four plots (2x2) on one single page;
• "time series";
• plot #1 (top left):
  • date & time of day (x-axis);
  • global active power (y-axis);
• plot #2 (top right):
  • date & time of day (x-axis);
  • voltage (y-axis);
• plot #3 (bottom left):
  • date & time of day (x-axis);
  • sub metering 1, sub metering 2, sub metering 3 (y-axis);
• plot #4 (bottom right):
  • date & time of day (x-axis);
  • global re-active power (y-axis).

Parameter	Description
dtPlt	data table containing the data to plot
fname	name of the file the plot has to sent to
imgSize	size/dimension (xx) of the plot generated and written to file

Table: Input parameter

Result	Description
TRUE	success; data have been plot both the screen as well as the file
FALSE	failure

Table: Output value

Note
All of dtPlt, fname, and imgSize have to be provided, and set to a non-NULL value.

lib/rduciepc.R

Read raw data (electric power consumption imported from the UC Irvine Machine Learning Repository) into a corresponding data structure.

The variable Date is getting converted into class POSIXct, and an additional variable DateTime time is created by executing

rc[, DateTime := dmy_hms(paste(Date, Time))]
rc[, Date := dmy(Date)]

(dmy_hms and dmy are provided by the lubridate package)

Parameter	Description
basedir	base directory to read files from
fname	file to read

Table: Input parameter

Result	Description
data table	success; data table containing the read raw data
NULL	failure

Table: Output value

Note

• both--baseDir and fname--have to be provided, and set to a non-NULL value.

lib/setusragnt.R

Set user agent to a "real" browser (instead of pointing to the R environment/session).

Parameter	Description
NONE

Table: Input parameter

Result	Description
NONE

Table: Output value

lib/sstuciepc.R

Extract a subset of the read raw data (electric power consumption imported from the UC Irvine Machine Learning Repository).

Parameter	Description
dtAll	data table containing the original data to be subsetted
fromDate	subset dtAll with Date >= fromDate
toDate	subset dtAll with Date <= toDate

Table: Input parameter

Result	Description
data table	success; data table containing the requested subset of the raw data
NULL	failure

Table: Output value

Note:

• all of dtAll, fromDate, toDate have to be provided, and set to a non-NULL value;
• fromDate and toDate are getting swapped in case fromDate is greater/later than toDate;
• fromDate and toDate have to be provided in the format year month day (with or without separators in between).

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