Vectors in R Programming

Though I’m new to the language, it is obvious that understanding vectors in R programming is an essential part of learning the language. This post is going to touch on some of the basics of vector implementation in R and examples of useful functions such as c(), seq(), rep().

Official documentation on basic vectors in R can be found here

All Variables in R are Vectors

Basically, all variables in R are vectors. This is validated by using the is.vector() function:

OneLenVec <- 99

With the code above, the result printed in the final statement is TRUE:

All variables are vectors.

The Combine Function

A simple way to create a vector is using the combine function.

> NumericVector <- c(78, 99, 1, -55, 22)
> print(NumericVector)
[1] 78 99 1 -55 22
> is.numeric(NumericVector)
[1] TRUE
> is.double(NumericVector)
[1] TRUE

Also seen above are some other new “is.XYZ” functions where the data type can be checked.

Vector Data Types are Homogeneous

Previously, the examples of vectors are obviously the same. However, a good example of how R handles mixed data types is vectors is seen below:

R simply converted all vector elements to be character strings because one of the elements was a character string.

Creating Vectors with Seq and Rep

When I first saw the “X:Y” syntax in for loops, I immediately thought of Python. Previous notes on for loops are captured in this blog post. However, the “X:Y” syntax does not support a third value to specify step as is seen in Python. However, the seq() function also can be used to create vectors, and it does support the step option.

The basic use of the sequence function is as follows:

basic_sequence <- seq(1, 10)
[1] 1 2 3 4 5 6 7 8 9 10
seq_with_step <- seq(1, 10, 3)
[1] 1 4 7 10

The rep() function is used to replicate vectors. First, remember that all variables are vectors, so the rep() function can be used as shown below:

single_char <- “a”
ten_chars <- rep(single_char, 10)
[1] “a” “a” “a” “a” “a” “a” “a” “a” “a” “a”

The function behaves, such that, it replicates the entire vector:

message <- c(“Replicate”, “me”)
print(rep(message, 3))
[1] “Replicate” “me” “Replicate” “me” “Replicate” “me”

Accessing Vector Elements

Vectors are indexed starting at 1 instead of 0 as in most other modern programming languages. That takes me back to Visual Basic.

Using the previous vector, MixedOrNot, I can get the second element as follows:

[1] “3943”

Another observation is the use of negative indexing. In Python, for example, imagine the following code:

python_array = [1, 2, 3, 4, 5, 6]

That will print the “negative 3rd indexed” item, which is 4.

In R, this actually removes the third item from the vector:

R vector with negative index

As expected, the “X:Y” syntax is supported (e.g. using r_vector) from the last screen shot:

[1] 1 2 3

There are some other creative ways to selectively pull elements from the vector. To, for example, pull the first, third, and fifth element of a vector one could:

print(r_vector[c(1, 3, 5)])
[1] 1 3 5

These combinations of “X:Y”, combine c(), and variations thereof provide a variety of ways to access elements of the vector.

This concludes the basic overview of vectors in R programming.

Categories: R Programming

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