R - Programming

 

Features Of R : 

1) R is a well-developed, simple and effective programming language which includes decision making , flow control, recursive, functions input and output methods

2) R has an effective data handling and storage facility which is important for statistical analysis.

3) R Provides a variety of operators for calculations on arrays, lists, vectors and matrices.

4) R provides a large, coherent and integrated collection of packages and tools for data analysis including mathematical symbols. Dynamic and interactive graphics are available through additional packages 

5) R and its libraries implement a wide variety of statistical and graphical techniques, including  linear and non linear modelling, classical statistical tests, time - series analysis, classification,clustering and others

6) R is easily extensible through function and extensions. R community is noted for its active contribution in terms of packages. For computationally intensive tasks, C, C++ and Fortran code van be linked and called at run time. Advanced users can write C/C++, Java , .NET or Python code to manipulate R objects directly

7) Since R was  inherited from a language called S , R has stronger objective-oriented programming facilities than  most statistical computation languages 

Identifiers:

The unique name given to variable like function or object is known as an identifier . Following are the rules for naming an identifier.

a)     Identifier can be a combination of letters, digits, period, and underscore(_).

b)     It must start with a letter or a period. If it starts with a period, it cannot be followed by a digit.

c)     Reserved word in R cannot be used as identifiers

Examples of some valid identifiers are: total, sum, .date, .date.of.birth,sum_of_two

Example of some invalid identifiers are : tot@l,2um, _prod, TRUE, .0wl

Earlier version of R used underscore  (_) as an assignment operator. So, the period (.) was used extensively in variable names having multiple words.

Constants :

Constants or literals, as the name suggest, are entities whose values cannot be altered. Basic type of constants are numeric and character constants. They are built-in constants also.  

All numbers fall under this category. They can be of type integer, double, or complex, We can check the type of constants by typeof() function.

Variables:

A variable provides us with named storage that our programs manipulate. A variable in R can store an atomic vector, group of atomic vectors or a combination of many R objects. A valid variable name consists of letters, numbers and the dot or underline characters. The rule for naming a variable is same as that of any identifiers which is already discussed above.

The variable can be assigned values leftward, rightward and equal to operator. The values of the variables can be printed using print () or cat ()function. The cat()  function combines multiple items into a continuous print output.

Operators :

R has several operator to perform tasks arithmetic, logical and bitwise operations. R provides following types of operators . They are

a)     Arithmetic operator

b)     Relational Operator

c)     Logical Operator

d)     Assignment Operator

e)     Miscellaneous Operator

Arithmetic operator:

These operators are used to carry out mathematical operations, like addition, subtraction, multiplication, division. The arithmetic operators are applied for vectors. Even if we give a single value, it is considered as a vector with length one.

 

  

Relational operator :

Relational operator are used to compare between values. Each element of the first vector is compared with the corresponding element of the second vector. The result of comparison is a Boolean value.

 

 

Logical operator :

 Logical operator are applicable only to vectors of type logical, numeric or complex. All numbers greater than 1 are considered as logical value TRUE. Each element of the first vector is compared with the corresponding element of the second vector. The result of comparison is Boolean value.

Operator	Description
!	Logical Not, Takes each element of the vector and gives the opposite logical value
&	Element wise logical And. It combines each element of the first vector with corresponding element of the second vector and gives an output TRUE if both the values are  TRUE.
&&	Logical AND. It takes first element of both the vectors and gives  TRUE only if both elements are TRUE
|	Element-wise logical OR. It combines each element of the first vector with the corresponding element of the second vector and gives an output TRUE if one of the elements is TRUE
||	Logical OR. It takes first element of both the vectors and gives an output TRUE if one of the element is TRUE

 

Assignment Operator :

These operators are used to assign values to variables or vectors. The operators <- and = can be used almost interchangeably to assign values to a variables in the same environment.

The <<- operator is used for assigning values to variables in the parent environments

Operators	Description
<-,<<-,=	Leftward assignment
->,->>	Rightward assignment

 

 

Miscellaneous operator :

These operator are used for specific purpose. They are not used for mathematical or logical computation.

Operators	Description
:	Colon. It creates a range of numbers in sequence for a vector.
%in%	This operator is used to check whether an element belongs to a vector or not. The result will be a Boolean value either TRUE or FLASE.
%*%	This operator is used to multiply a matrix with its transpose

 

 

Strings:

Strings are created in R by writing any value within a pair of single quote or double quotes. However, internally R stores every strings within  double quotes, even if we create them with single quote. The quotes at the beginning and end of a string should be both double quotes or both single quotes. They cannot be mixed. Another feature of string is that double quotes can be inserted into a string staring and ending with single quote. Similarly single quote can be inserted into a string a staring and ending with double quotes.

Reading String :

We can read string from keyboard using the readLines () function . It lets the user to enter one-line string at the terminal . The syntax as follows :

a <- readLines("stdin", n=1);