If you need a set of random numbers, e.g., for simulations, this might be the right article for you. In this article, we explain several ways to create a vector with random numbers in R.
We discuss the most common R functions to generate random numbers, such as random integers, random numbers between 0 and 1, and random samples with(out) replacement.
How to Create a Vector with Random Integers
One of the most used samples in R are vectors with randomly generated integers (i.e., whole numbers). Generating such a sample is easy.
You create a vector with random integers with the sample() function. This native R function has two obligatory arguments, namely the integers from which you want to sample, and the number of samples you want to take. A third, optional argument, tells R to sample with or without replacement.
The first argument, the population from which R takes a sample, can have different forms. For examples:
- A continious list of integers, e.g., -5:5
- A discontinious list of integers, e.g. c(1, 3, 5)
- A combintion of the two list above, e.g., c(-5:0, 2, 4)
The second argument, the sample size, must be a positive whole number.
In the example below, we create a sample of 10 randomly generated integers between -5 and 5. We use the set.seed() function so that you can replicate the outcome.
set.seed(123)
x <- sample(-5:5, size = 10)
x
As the image shows, all of the generated numbers appear exactly once. This is because we’ve generated a sample without replacement. However, if needed, you can use the sample() function to create a sample with replacement.
You create a random sample with replacement using the replace=-option. By default, this option is set to False. However, if you use replace = TRUE, R samples with replacement, and hence your sample might contain a specific number more than once.
For example, in the R code below, we use the replace=-option to create a vector with random integers.
set.seed(123)
x <- sample(-5:5, size = 10, replace = TRUE)
xAs the outcome shows, the numbers 0 and 4 appear twice.
If you want to know how to create rounded random numbers (e.g., to 2 decimals places), please read this article.
Sample Error
A common error while using the sample() function is the following:
Error in sample.int(length(x), size, replace, prob): cannot take a sample larger than the population when 'replace = FALSE'
This error indicates that the desired sample size is larger than the population from which you take the sample. For example, below we try to take a sample of 100 integers from a population of 11 numbers (-5, -4, -3, -2, -1, 0 , 1, 2, 3, 4, 5).
Because we sample without replacement and the sample size is larger than the population size, R returns the error.
You can solve this error by:
- Increae the population size (first argument), or
- Decrease the sample size (second argument), or
- Add the replace-option to sample with replacement (third argument)
How to Create a Vector with Random Numbers between 0 and 1
Another frequently used sample is a set of random numbers between 0 and 1.
You create a vector with randomly generated numbers between 0 and 1 with the runif() function. This basic R function has three arguments:
- A positive integer that specifies the sample size.
- The minimum of the sample population. If you want to generate a sample with numbers between 0 and 1, you should set this argument to 0.
- The maximum of the sample population. If you want to genereate a sample with numbers between 0 and 1, you should set this argument to 1.
The R code below shows how to use the runif() function to create a sample of 10 observations with numbers between 0 and 1. We use the set.seed() function replicability.
set.seed(123)
x <- runif(10, min = 0, max = 1)
x
Although the runif() is frequently used to create samples with numbers between 0 and 1, you can use this function also to generate samples with other sample populations. For example, below we create a vector of 10 elements with random numbers between -5 and 5.
set.seed(123)
x <- runif(10, min = -5, max = 5)
x
How to Create a Vector with Random Numbers from the Normal Distribution
In R, you can also create a vector with a sample from a Normal Distribution.
To generate numbers from a Normal Distribution, you use the rnorm() function. This function has 3 arguments, namely the sample size, and the mean and standard deviation of the normal distribution.
In the example below, we use the rnorm() function to create a sample of 10 observations from the Standard Normal Distribution. That is to say, a normal distribution with a mean of 0 and a standard deviation of 1.
set.seed(123)
x <- rnorm(10, mean = 0, sd = 1)
x
We could’ve written the code above a bit shorter because we could’ve omitted the mean=-option and the sd=-option. If you don’t specify the mean and standard deviation, R automatically assumes that you want to create a sample from the standard normal distribution.
Likewise, you could also set the mean=-option and the sd=-option to other values to generate samples from another standard deviation. Below we generate 10 samples from the normal distribution with mean = 5 and standard deviation = 1.5.
set.seed(123)
x <- rnorm(10, mean = 5, sd = 1.5)
x
How to Create a Binary Vector
Another type of random sample is the binary sample. This sample contains only 0’s and 1’s.
You can create a binary sample with the sample() function. First, you specify the sample population (i.e., 0 and 1), followed by the sample size and the replacement argument.
Note that, if you want to create a binary vector with more than 2 observations, you need to set the replace=-option to True.
Below, we create a random binary vector of 10 observations.
set.seed(123)
x <- sample(0:1, size = 10, replace = TRUE)
x
How to Create a Vector with Random Characters
So far, we’ve discussed how to create vectors with random numbers. Instead of numbers, R can also generate vectors with random characters.
You create a sample of randomly selected characters with the sample() function. The sample() function has two mandatory arguments:
- A list of characters that serves as the sample population. For example, c(“A”, “B”, “C”).
- A positive integer that specifies the sample size.
In the example below, we create a sample of 3 characters from the letter A to E.
set.seed(123)
x <- sample(c("A", "B", "C", "D", "E"), size = 3)
x
If you want to take a sample of all 26 letters of the alphabet, but you don’t want to write them all out as the first argument, you can use the reserved word LETTERS. This reserved word contains all 26 letters of the alphabet in uppercase.
Below we use the reserved word LETTERS to generate efficiently a sample of 3 letters.
set.seed(123)
x <- sample(LETTERS, size = 3)
x
Note that, if you want to take a sample from the alphabet in lowercase, you can use the reserved word letters. You can also combine both reserved words to create a sample with lower- and uppercase letters (c(letters, LETTERS)).
How to Create a Vector with Random Strings
Above we have shown how to create a sample of random characters. If you want to generate random strings (i.e., a combination of multiple characters), then this method doesn’t work. However, there does exist an easy way to create random strings in R.
You create random strings in R with the stri_rand_strings function from the stringi packages. To create the strings, you must provide two arguments:
- A positive integer that indicates the number of strings you want to generate.
- A positive integer that indicates the length of each string.
In the example below, we use the sitri_rand_strings() function to generate 3 random strings of length 5.
if (!require("stringi")) install.packages("stringi")
set.seed(123)
x <- stri_rand_strings(3, 5)
x
As you can see, the stri_rand_strings() function generates strings that consist of letters (lower- and uppercase) and numbers. You can use the pattern=-option to specify the characters that can be part of the strings.
In the example below, we use the pattern=-option to generate strings that only contain letters (both lower- and uppercase).
if (!require("stringi")) install.packages("stringi")
set.seed(123)
x <- stri_rand_strings(3, 5, pattern = "[A-Za-z]")
x
