## Saturday, 13 January 2018

### What is Vector Indexing in R Programming and How to form a SubVector

How to form a SubVector with Vector Indexing in R Programming
One of the most important and frequently used operations in R is that of indexing vectors, in which we form a SubVector by picking elements of the given vector for specific indices or index positions. The format is Vector1[Vector2], with the result that we select those elements of Vector1 whose indices are given in Vector2.
Example :
> y <- c(1.2, 3.9, 0.4, 0.12)
> y
[1] 1.20 3.90 0.40 0.12

# Extracting elements 1 and 3 of y
> y[c(1,3)]
[1] 1.2 0.4

# Extracting elements 3 and 4 of y
> y <- c(1.2, 3.9, 0.4, 0.12)
> v <- 3:4
> y[v]

[1] 0.40 0.12
> y[3:4]
[1] 0.40 0.12

#Please Note that the duplicates are also allowed in SubVector.
> x <- c(4,2,17,5)
> y <- x[c(1,1,3)]
> y
[1] 4 4 17

Negative Subscripts
Negative subscripts mean that we want to exclude the given elements in our output.
> z <- c(5,12,13)
> z
[1]  5 12 13
# excluding a element in output.
> z[-2]
[1]  5 13

#Please note that the Elements will exclude only in Output but not from the actual source Vector.
> z
[1]  5 12 13

To exclude elements, it is often useful to use the length() function. For instance, suppose we wish to pick up all elements of a vector z except for the last. The following code will do just that:
> z <- c(5,12,13)
> z[1:(length(z)-1)]
[1] 5 12
or you can write simply as below, where we passing the length of z as negative index z[-3] .
> z[-length(z)]
[1] 5 12

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