How to Create and Manipulate Variables and Vectors in R
What is a Variable and what is a Vector
Definition of a variable Variables are objects in R that you can use to store values. It can consist of a single value, basic or complex arithmetic operations, or even be more complex such as a column in a data matrix or a data frame. We will see these complex forms in the following steps of this course. Definition of a vector A vector is substantially a list of variables, and the simplest data structure in R. A vector consists of a collection of numbers, arithmetic expressions, logical values or character strings for example. However, each vector must have all components of the same mode, that are called numeric, logical, character, complex, raw.How to create and manipulate Variables
Step 1. We recommend you to work in the same working subdirectory that you created previously for analyses conducted with R. If the subdirectory is not created yet or mistakenly removed, please do it again, and launch R$ mkdir exerciseR
$ cd exerciseR
$ R
$ R
> setwd("/Users/imac/Desktop/exerciseR")
> getwd()
[1] "/Users/imac/Desktop/exerciseR"
> x < 3 * 4 + 2 * 5 + 3
> x = 3 * 4 + 2 * 5 + 3
> x
[1] 25
> y < x^4  4*x + 5
> x
[1] 390530

 Variable names can contain letters, numbers, underscores and periods

 Variable names cannot start with a number or an underscore

 Variable names cannot contain spaces at all
> x.length < 3*2
> x.length
[1] 6
> _x.length < 3*2
Error : unexpected input in "_"
> 3x.length < 3*2
Error : unexpected symbol in "3x.length"

 Periods to separate words: x.y.z

 Underscores to separate words: x_y_z

 Camel Case to separate words: XxYyZz
> x.length < 3*2
> x.length
[1] 6
> x_length < 3*2
> x_length
[1] 6
> xLength < 3*2
> xLength
[1] 6
How to create and manipulate Vectors
Step 1. A vector can be created using an inbuilt function in R called c(). Elements must be commaseparated.> c(10, 20, 30)
[1] 10 20 30
> c(1.1, 2.2, 3.5) # numeric
[1] 1.1 2.2 3.5
>
> c(FALSE, TRUE, FALSE) # logical
[1] FALSE TRUE FALSE
>
> c("Darth Vader", "Luke Skywalker", "Han Solo") # character
[1] "Darth Vader" "Luke Skywalker" "Han Solo"
> assign("x", c(10, 20, 30))
> x
[1] 10 20 30
>
> x < c(10, 20, 30)
> x
[1] 10 20 30
>
> x = c(10, 20, 30)
> x
[1] 10 20 30
>
> c(10, 20, 30) > x
> x
[1] 10 20 30
> v < numeric()
> w < character()
> mode(x)
[1] "numeric"
> mode(v)
[1] "numeric"
> mode(w)
[1] "character"
>
> length(x)
[1] 3
> x < c(10, 20, 30)
> x
[1] 10 20 30
> 1/x
[1] 0.10000000 0.05000000 0.03333333
> x < c(10, 20, 30)
> y < x*3+4
> y
[1] 34 64 94
> z < c(x, 0, 0, 0, x)
> z
[1] 10 20 30 0 0 0 10 20 30
> w < 2*x + y + z
> w
[1] 64 124 184 54 104 154 64 124 184
> mean(x)
[1] 20
> var(x)
[1] 100
> sort(z)
[1] 0 0 0 10 10 20 20 30 30
> a < c(1:10)
> a
[1] 1 2 3 4 5 6 7 8 9 10
> b < rep(a, times=2)
> b
[1] 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10
> b < rep(a, each=2)
> b
[1] 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10
> c < seq(2, 2, by=.5)
> c
[1] 2.0 1.5 1.0 0.5 0.0 0.5 1.0 1.5 2.0
> x==x
[1] TRUE TRUE TRUE
> x==y
[1] FALSE FALSE FALSE
> x!=y
[1] TRUE TRUE TRUE
> x
[1] 10 20 30
> x[3]
[1] 30
> x[3] < 50
> x
[1] 10 20 50
> length(x)
[1] 3
> dairy < c(10, 20, 1, 40)
> names(dairy) < c("milk", "butter", "cream", "yogurt")
> breakfast < dairy[c("milk","yogurt")]
> breakfast
milk yogurt
10 40
Discussion
Now try it yourself and discuss in the comment area below: Question 1. Did you manage to create and manipulate Variables? Question 2. Did you manage to create and manipulate Vectors?Exercise
Let’s try it ! Question 1. Could you create 3 vectors: a vector x containing the numbers 3, 10 and 30 a vector m containing the content of x repeated twice a vector n containing two copies of x separated by a 0 Question 2. Is the content of m equal to the content of n? Question 3. Note that you should also obtain a warning message because the 2 vectors are not of the same length. How can you check the length of both vectors?Bioinformatics for Biologists: An Introduction to Linux, Bash Scripting, and R
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