R: Accessing elements of a vector

You can access elements of vector using indexes.

> vector1 <- c("h", "e", "l", "l", "o", "vector")
> vector1[1]
[1] "h"
> vector1[2]
[1] "e"
> vector1[3]
[1] "l"
> vector1[4]
[1] "l"
> vector1[5]
[1] "o"
> vector1[6]
[1] "vector"

Unlike other languages, indexes in R start from 1.

Negative indexes

If the index is negative, then it return all the members, other than one member whose position has the same absolute value as the negative index.

> vector1
[1] "h"      "e"      "l"      "l"      "o"      "vector"
> vector1[-1]
[1] "e"      "l"      "l"      "o"      "vector"
> vector1[-2]
[1] "h"      "l"      "l"      "o"      "vector"
> vector1[-3]
[1] "h"      "e"      "l"      "o"      "vector"
> vector1[-4]
[1] "h"      "e"      "l"      "o"      "vector"
> vector1[-5]
[1] "h"      "e"      "l"      "l"      "vector"
> vector1[-6]
[1] "h" "e" "l" "l" "o"

Range index

You can retrieve the elements of vector, from start index to stop index.

Syntax

vectorName[start:stop]

Returns elements from start to stop (inclusive).

> vector1
[1] "h"      "e"      "l"      "l"      "o"      "vector"
> vector1[2:4]
[1] "e" "l" "l"
> vector1[1 : length(vector1)]
[1] "h"      "e"      "l"      "l"      "o"      "vector"

You can get a new vector, by using the specific indexes from given vector.

> vector1[1 : length(vector1)]
[1] "h"      "e"      "l"      "l"      "o"      "vector"
> 
> vector1[c(2, 5)]
[1] "e" "o"
> vector1[c(2, 1,5,6)]
[1] "e"      "h"      "o"      "vector"

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