R - Vector

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1 - About

The Vector in R contains elements of the same class.

A Vector with different class of objects is a list.

A vector (as every object) can also have names.

Almost all data in R is a vector or is based upon vectors:

The elements of a vector in R have an explicit order, and each element can be individually indexed. R's in-memory processing relies on this order of elements for many computations, e.g., computing quantiles and summaries for time series objects.

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3 - Syntax

3.1 - Constructor

vector(mode = "logical", length = 0)

where:

  • mode is the class
  • length is the number of element

Example of:

  • an empty vector (logical of length 1)
> v=vector()
> v
logical(0)
  • an integer vector of length 2
> x = vector(mode = "integer", length = 2)
> x
[1] 0 0
> str(x)
 int [1:2] 0 0

The [1] indicates that x is of the vector class

3.2 - Combine

myVector <- c(object,object,...)  

where c is the combine function. The default method combines its arguments to form a vector.

Example:

> c(1,2)
[1] 1 2
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3.3 - Sequence

s = seq(from=1,to=4)
> s
[1] 1 2 3 4

3.4 - Repeat

vector = rep(0,5)
[1] 0 0 0 0 0

4 - Atomic vector types

There are 6 basic/atomic vector types:

  • logical: a boolean value (for example: TRUE)
  • integer: an integer value (for example: 1)
  • numeric (double): a real number (for example: 1.5)
  • character: a character string (for example: “foobar”)
  • complex: a complex number (for example: 1+2i)
  • raw: bytes

5 - Class Hierarchy

The following class hierarchy occurs when creating an vector with several different object classes:

  1. NULL
  2. list
  3. expression

This operation is named: coercion.

Example:

> v = c(NULL, TRUE)
> class(v)
[1] "logical"
> v = c(TRUE, 2)
> class(v)
[1] "numeric"
> v = c(1, "Nico") 
> class(v)
[1] "character"
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6 - Attributes

6.1 - Names

> v = 1:2
> names(v)
NULL
> names(v)=c("Nic","o")
> names(v)
[1] "Nic" "o"  
> v
Nic   o 
  1   2 

7 - Operations

See R - (Mathematical|Logical) Operators

Many operations in R are vectorized.

> x=1:4;y=6:3
> x
[1] 1 2 3 4
> y
[1] 6 5 4 3
> z =2
> z
[1] 2
> w=c(2,4)
> w
[1] 2 4

7.1 - Addition

# Addition
> x+y
[1] 7 7 7 7
> x+z
[1] 3 4 5 6
> x+w
[1] 3 6 5 8

7.2 - Distinct / Unique

unique(x)

7.3 - Others

# Multiplication
> x*y
[1]  6 10 12 12
# Division
> x/y
[1] 0.1666667 0.4000000 0.7500000 1.3333333
# Power
> x^y
[1]  1 32 81 64
# Logical
> x>2
[1] FALSE FALSE  TRUE  TRUE
> x>=2
[1] FALSE  TRUE  TRUE  TRUE
> y==1
[1] FALSE FALSE FALSE FALSE

8 - How to

8.1 - Subset

> v=1:5
> v
[1] 1 2 3 4 5
  • Indexing
> v[2]
[1] 2
  • Slicing
> v[3:5]
[1] 3 4 5
> v[5:3]
[1] 5 4 3
  • Condition
> v[v>3]
[1] 4 5
> c=v>3
> c
[1] FALSE FALSE FALSE  TRUE  TRUE
> v[c]
[1] 4 5
  • Condition with replace
v=1:5
v[v<3]=0
v
[1] 0 0 3 4 5

8.2 - Remove missing values (NAs)

How to remove NAs value:

  • on one object
> v = c(1, 2, NA, 4, NA, 6)
> nas = is.na(v)
> nas
[1] FALSE FALSE  TRUE FALSE  TRUE FALSE
> v[nas]
[1] NA NA
> v[!nas]
[1] 1 2 4 6
  • with multiples objects where NA is not present in the column of all objects
> v = c(1, 2, NA, 4, NA, 6)
> v2 = c("Nico",NA,"Mad",NA,"Mel","Ri")
> notNa = complete.cases(v, v2)
> notNa
[1]  TRUE FALSE FALSE FALSE FALSE  TRUE
> v[notNa]
[1] 1 6
> v2[notNa]
[1] "Nico" "Ri"

9 - Function

9.1 - Length

> v <- c(1,-2,3.3,7,-3)
> length(v)
[1] 5

9.2 - Str

Data Structure

> v <- c(1,-2,3.3,7,-3)
> str(v)
 num [1:5] 1 -2 3.3 7 -3

where

  • num: indicates the numeric class
  • [1:5]: from one to 5 elements
  • 1 -2 3.3 7 -3: the elements
lang/r/vector.txt · Last modified: 2017/07/06 15:07 by gerardnico