Vectors

Feeling a bit limited in what you can do so far? No worries, let's level up our programming skills. You probably heard about vectors in high-school, probably in Physics and Mathematics. Remember, this arrow having a length and a direction? Well, forget about it :). Vectors in R have nothing to do with this. What is nice is that they are more simple, much more simple!

Vocabulary: A vector is the simplest R data structure consisting of a collection of numeric or character values (there are other types of vectors but that will not be covered here).

In the examples below, you will see different manners to create vectors and to access their elements.

> ## A first way to declare numeric vector
> vector("numeric", 10)
> ## And character vectors
> vector("character", 5)

Maybe you would like to control what is inside your vector:

> ## Generate a serie of numbers from 5 to 15
> 5:15
> ## Generate letters from A to D
> ## The function LETTERS generate A-Z
> LETTERS
> ## Now subselect the first four letters
> LETTERS[1:4]
> ## Generate vectors with combine
> c(1,2,3)
> c("A", "B", "C")

Question: What would happen if you mix numbers and characters when creating a vector?

Exercise 4:

• Create two vectors with 'combine' and affect the results to two variables
• Use the created variables to combine them in a third one!
• Create a vector with values from 11 to 25 (use the symbole ':') and store the result in a new variable
• Access the first element of the vector
• Modify the value of the fifth element

Finally, let' see how to combine numbers and characters:

> genes <- c(100,205,348,345)
> names(genes) <- c("CHD8","MALAT1","HoxC","Nanog")
> genes
> genes[2]
> genes["HoxC"]

Question: What would happen if you give more names than values?

'names()' is a function. This is the first one that we see!