Vector in R programming.
Vectors in R
The term vector might sound intimidating. In R programming,
a vector is the most-used data object. Like its counterpart in C++, it is a
dynamic array of elements, each of the same data type. Another way to think of
a vector is that it is a list of values, such as ratings, names, scores,
prices, etc.
Another important property of a
vector is its length. This is the number of elements in the vector and can be
checked with the function length().
How to Create Vector in R?
Vectors are generally created
using the c() function.
Since, a vector must have
elements of the same type, this function will try and coerce elements to the
same type, if they are different.
Coercion is from lower to
higher types from logical to integer to double to character.
>
x <- c(1, 5, 4, 9, 0)
>
typeof(x)
[1]
"double"
>
length(x)
[1]
5
>
x <- c(1, 5.4, TRUE, "hello")
>
x
[1]
"1" "5.4" "TRUE" "hello"
>
typeof(x)
[1]
"character"
How to access
Elements of a Vector?
Elements of a vector can be accessed using vector
indexing. The vector used for indexing can be logical, integer or character
vector.
Using integer vector as index
Vector index in R starts from 1, unlike most programming
languages where index start from 0.
We can use a vector of integers as index to access
specific elements.
We can also use negative integers to return all elements
except that those specified.
But we cannot mix positive and negative integers while
indexing and real numbers, if used, are truncated to integers.
> x[1] 0 2 4 6 8 10> x[3] # access 3rd element[1] 4> x[c(2, 4)] # access 2nd and 4th element[1] 2 6> x[-1] # access all but 1st element[1] 2 4 6 8 10> x[c(2, -4)] # cannot mix positive and negative integersError in x[c(2, -4)] : only 0's may be mixed with negative subscripts> x[c(2.4, 3.54)] # real numbers are truncated to integers[1] 2 4
Using logical vector as index
When we use a logical vector for indexing, the position
where the logical vector is
TRUE is returned.
This useful feature helps us in filtering of vector as
shown below.
> x[c(TRUE, FALSE, FALSE, TRUE)][1] -3 3> x[x < 0] # filtering vectors based on conditions[1] -3 -1> x[x > 0][1] 3
In the above example, the expression
x>0 will
yield a logical vector (FALSE, FALSE, FALSE, TRUE) which
is then used for indexing.
Using character vector as index
This type of indexing is useful when dealing with named
vectors. We can name each elements of a vector.
> x <- c("first"=3, "second"=0, "third"=9)> names(x)[1] "first" "second" "third" > x["second"]second 0 > x[c("first", "third")]first third 3 9
How to modify a
vector in R?
We can modify a vector using the assignment operator.
We can use the techniques discussed above to access
specific elements and modify them.
If we want to truncate the elements, we can use
reassignments.
> x[1] -3 -2 -1 0 1 2> x[2] <- 0; x # modify 2nd element[1] -3 0 -1 0 1 2> x[x<0] <- 5; x # modify elements less than 0[1] 5 0 5 0 1 2> x <- x[1:4]; x # truncate x to first 4 elements[1] 5 0 5 0
How to delete a
Vector?
We can delete a vector by simply assigning a
NULL to
it.> x[1] -3 -2 -1 0 1 2> x <- NULL> xNULL> x[4]NULL
Thank You,
Er. Shrikant Shejwal.
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