Wednesday 5 September 2018

Basics Calculations: Matrix Operations in R Language

In R, a 4 ๐—‘ 2-matrix X can be created with a following command:

> x <-  matrix (nrow=4,   ncol=2,  data=c(1,2,3,4,5,6,7,8)  )

> x
                [,1]       [,2]
[1,]             1          5
[2,]             2          6
[3,]             3          7
[4,]             4          8

Properties of a Matrix

We can get specific properties of a matrix:


> dim (x)         # tells the
[1]   4   2             dimension of matrix

> nrow (x)       # tells
[1]  4                    the number of rows

> ncol (x)        # tells 
[1]  2                  the number of columns

> mode (x)      # Informs the type or storage mode of an object, e.g., numerical, logical etc.
[1]   "numeric"
attributes provides all the attributes of an object

> attributes (x)    # Informs the dimension of matrix 
$dim   [1]    4   2

Help on the Object "Matrix"

To know more about these important objects, we use R-help on "matrix".
> help ("matrix")
matrix     package:base            R Documentation
Matrices
Description :
'matrix'  creates a matrix from the given set of values.
'as.matrix' attempts to turn its argument into a matrix.
'is.matrix'  tests if its argument is a (strict) matrix. It is generic: you can write methods to handle specific classes of objects, see Internal Methods.

Then we get an overview on how a matrix can be created and what parameters are available:

Usage :
   matrix(data  [= NA, nrow = 1 , ncol = 1, byrow = FALSE, dimension = NULL)
  as.matrix (x)
  is. matrix (x)

Arguments :
  data: an optional data vector.
  nrow: the desired number of rows
  ncol: the desired number of columns
  byrow: logical. If 'FALSE' (the default) the matrix is filled by columns, otherwise the matrix is filled by rows.

dimnames:  A 'dimnames'  attribute for the matrix: a 'list' of length 2.
        x: an R object.

Finally, references and cross-references are displayed...
References :
  Becker, R. A.,  Chambers, J. M. and wilks, A.
  R. (1988)  _The New S Language_. wadsworth & Books/Cole.

See Also:
  'data.matrix' , which attempts to convert to a numeric matrix.
.... as well as an example:

Examples :
  is.matrix (as.matrix (1 : 10) )
  data (warpbreaks)
  ! is.matrix(warpbreaks) #  data.frame, NOT matrix!
  warpbreaks [1 : 10,]
  as.matrix(warpbreaks[1 : 10,])  #using
      as.matrix.data.frame(.) method


Matrix Operations 

Assigning a specified number to all matrix elements:

> x  <-  matrix (nrow=4, ncol=2, data=2 )
> x 
             [,1]    [,2]
[1,]         2        2
[2,]         2        2
[3,]         2        2
[4,]         2        2

Construction of a diagonal matrix, here the identity matrix of a dimension 2:

> d  <-  diag (1,  nrow=2,  ncol=2)
> d
        [,1]   [,2]
[1,]    1       0
[2,]    0       1




Transpose of a matrix x:  x'

>  x  <- matrix (nrow=4, ncol=2, data=1:8,  byrow=T )
>  x
                [,1]      [,2]
[1,]             1          2
[2,]             3          4
[3,]             5          6
[4,]             7          8

Multiplication of a matrix with a constant



0 Comments:

Post a Comment

Popular Posts

Categories

AI (31) Android (24) AngularJS (1) Assembly Language (2) aws (17) Azure (7) BI (10) book (4) Books (146) C (77) C# (12) C++ (82) Course (67) Coursera (195) Cybersecurity (24) data management (11) Data Science (106) Data Strucures (8) Deep Learning (11) Django (14) Downloads (3) edx (2) Engineering (14) Excel (13) Factorial (1) Finance (6) flask (3) flutter (1) FPL (17) Google (20) Hadoop (3) HTML&CSS (47) IBM (25) IoT (1) IS (25) Java (93) Leet Code (4) Machine Learning (46) Meta (18) MICHIGAN (5) microsoft (4) Pandas (3) PHP (20) Projects (29) Python (876) Python Coding Challenge (281) Questions (2) R (70) React (6) Scripting (1) security (3) Selenium Webdriver (2) Software (17) SQL (42) UX Research (1) web application (8)

Followers

Person climbing a staircase. Learn Data Science from Scratch: online program with 21 courses