1. Programming For Big Data
Darren Redmond

2. Programming with R
R is programming language and integrated suite of software with facilities for data manipulation, calculation and graphical display
R is widely used for statistical software development and data analysis
R is based on “S” programming language
Try R -

3. Introduction
It runs on a variety of platforms including Windows, Mac OS and Linux
It contains advanced statistical routines
It has a large, coherent, integrated collection of intermediate tools for data analysis
R is highly extensible through the use of packages
Powerful graphics capabilities

4. Hello World Hello World!
Very simple to implement a Hello World! program with R:
print(“Hello World”)

5. R Expressions & Operators
An expression may also be a single literal or variable
Assignment
In R we assign a value to a variable using the assignment operators
<- =
->

6. R Operators Operator Description Example Result + Addition 2 + 3 5 -
Subtration (binary operator)
3 - 2 1
Negation (unary operator) -3 *
Multiplication
7*5 35 /
Division
5/3 %%
Modulus
34 %% 2
%/%
Integer Division
6%/%4
^ or **
Exponentiation
2^3 8

7. Precedence and Conversions
Operator precedence in R from highest to lowest
^ exponentiation (right to left)
- + unary minus and plus
%any% special operators (including %% and %/%)
* / multiply, divide
+ - (binary) add, subtract
Data Type Conversions
Use is.foo to test for data type foo. Returns TRUE or FALSE Use as.foo to explicitly convert it.
is.numeric(), is.character(), is.vector(), etc. as.numeric(), as.character(), as.vector(), etc.

8. Statements Sequence Statements
Instructions given in a sequence
Have a begin and an end point
In Class Example – transform from Celsius To Fahrenheit
celciusInput <- readline("please enter a Celcius value:")
celciusNumeric <- as.numeric(celciusInput)
fahrResults <- ((9/5)*celciusNumeric)+32
fahrString <- sprintf("%.2f", fahrResults)
message <- paste("the result is", fahrString, sep=" ")
print(message)

9. The simple if statement
R syntax
Program control: if the condition is true then the expr is executed otherwise the expr is skipped.
Python vs. R example
The if-else statement
Program control: if the condition is true then the expr1 is executed, otherwise the expr2 is executed.

10. Repetition Statements
A repetition statement tells the program to execute the program repeatedly
The while statement
R syntax
while (loop) expression
Program control: while the loop-continuation-condition is true the expr is executed
Example:
The for statement
Is a counter-controlled loop => you know how many times the loop will execute
for (count in c(1, 2, 3)) {
print(count) }
Program control: the expr are repeated for each item in the sequence

11. Datatypes in R atomic types Vectors List Factor data.frame
Numeric, Integer, complex, logical, character
Vectors
sequence of data elements of the same basic type
mutable (i.e., their values can change once created)
List
generic vector containing other objects
Factor
vector augmented with information about the possible categories, called the levels of the factor
data.frame
a table-like structure
experimental results often collected in this form

12. Functions
A sequence of reusable statements that performs a desired operation
Contains a header and a body
R syntax without a return value
functionName <-function(list of parameters){
funtionStatementblock }
R syntax with a return value
return(Expression)

13. Function Implementation
factorial <- function(n) {
if (n == 0) {
return(1)
} else {
return(n * factorial(n - 1)) }
average <- function(number1, number2) {
return ((number1 + number2) / 2)

14. Function Calling Local vs. global variables >average(5, 6) 5.5
Variables declared inside the function are local variables and cannot be used outside the function
Global variables can be accessed anywhere in the program including inside functions
>average(5, 6)
5.5
>factorial(5)
120

15. File Input / Output File open File close
myfile = file(“cities.txt”, open = “w”)
myfile
File close
close(myfile)

16. File Modes Open Mode Description “r” or “rt”
Opens a file for reading in text mode
“w” or “wt”
Opens a file for writing in text mode
“a” or “at”
Opens a file for appending data the end of the file
“rb”
Opens a file for reading binary data
“wb”
Opens a file for writing binary data
“r+”
Opens a file for reading and writing in text mode

17. Summary Introduction Expressions Statements Data types & Structures
Functions
File Input Output
22/04/2019