Friday, 10 August 2018

Data Management : Vector indexing in R Language

A vector of positive integers (letters, and Letters return the 26 lowercase and uppercase letters, respectively).

> letters [1 : 3]
 [1] "a"  "b"  "c"

> letters [c(2,4,6) ]
 [1]  "b"  "d"  "f'"

> LETTERS [1 : 3]
  [1]  "A"  "B"  "C"

> LETTERS [ c(2,4,6) ]
  [1]  "B"  "D"  "E"

> letters
 [1]  "a"  "b"  "c"  "d"  "e"  "f"  "g"  "h"  "i"  "j"  "k"  "l"  "m"  
[14] "n"  "o"  "p"  "q"  "r"  "s"  "t"  "u"  "v" "w"  "x"  "y"  "z" 
>
> LETTERS
 [1]  "A"  "B"  "C"  "D"  "E"  "F"  "G"  "H"  "I"  "J"  "K"  "L"  "M"
[14]  "N"  "O"  "P"  "Q"  "R"  "S"  "T"  "U"  "V"  "W"  "X"  "Y"  "Z"
>
> letters [1] 
 [1]  "a" 
>
> letters [14]
 [1]  "n"
>  Letters [1]
  [1]  "A"
> LETTERS [14]
 [1]  "N"
> letters [c(12,20,26) ]
 [1]  "1"  "t"  "z"


String vector
→ The elements of a vector can be named.
      Using these names, we can access the vector elements.

names is used for functions to get or set the names of an object.
> z <- list (al = 1, a2 = "c" , a3 = 1 :3)
> z
$al
 [1]  1
$a2
 [1]  "c"
$a3
 [1] 1 2 3

> names (z)
[1]  "a1"  "a2"  "a3"

Matrices created from Lists

List can be heterogeneous (mixed modes).
We can start with a heterogeneous list, give it dimensions, and thus create a heterogeneous matrix that is a mixture of numeric and character data:
Example
> ab  <- list (1, 2, 3, "x", "y" , "z")
> dim(ab)  <- c(2,3)
> print(ab)
      [,1]  [,2]  [,3]
[1,]   1     3      "y"
[2,]   2    "x"    "z"




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