How to Use runif in R (Practical Examples)

Renesh Bedre    3 minute read

runif() function from R generates random numbers from uniform distribution.

In uniform distribution, every value within the given range is equally likely to occur. Uniform distribution is mostly used in the generation of random numbers.

The general syntax of runif() looks like this:

runif(n, min = 0, max = 1)

Where,

Parameter Description
n number of random numbers to generate
min minimum value for the random numbers (default is 0)
max maximum value for the random numbers (default is 1)

The following examples demonstrate how to use the runif() (random uniform) function to generate random numbers.

Example 1: Generate random numbers between 0 and 1

By default, the runif() function generates random numbers between 0 to 1 from a uniform distribution.

The following example shows how to generate 10 random numbers between 0 and 1 using runif().

If you run the runif() function multiple times, you may see different results every time. To get reproducible random results every time, you should use set.seed() function.

# for reproducible random result
set.seed(1)

# generate 10 random values between 0 to 1
runif(10)

# output
 [1] 0.62911404 0.06178627 0.20597457 0.17655675 0.68702285 0.38410372 0.76984142 0.49769924
 [9] 0.71761851 0.99190609

You can see that the 10 random values between 0 and 1 are generated from the uniform distribution.

Example 2: Generate random numbers between 1 and 100

The following example shows how to generate 10 random numbers between 1 and 100 from uniform distribution using runif().

# for reproducible random result
set.seed(1)

# generate 10 random values between 1 to 100
runif(10, 1, 100)

# output
[1] 38.623483 77.967077 93.535818 22.002110 65.515703 13.429955 27.454846 39.225295
 [9]  2.325643 38.856408

You can see that the 10 random values between 1 and 100 are generated from the uniform distribution.

Example 3: Generate random integer numbers between 1 and 100

From the above examples, you have seen that runif() function generates floating numbers.

You can use either round (gives nearest integer) or floor (rounds down to nearest integer) to get the integer values from a uniform distribution

# for reproducible random result
set.seed(1)

# generate 10 random integer values between 1 to 100 using round
round(runif(10, 1, 100))

# output
[1] 27 38 58 91 21 90 95 66 63  7

set.seed(1)
# generate 10 random integer values between 1 to 100 using floor
floor(runif(10, 1, 100))

# output
[1] 27 37 57 90 20 89 94 66 63  7

You can see that the 10 random integer values between 1 and 100 are generated from the uniform distribution.

Example 4: Generate histogram from uniform distribution

You can also runif() function to generate random numbers and plot a histogram of uniform distribution (rectangular distribution).

The following example generates 1000 random numbers and plots a histogram,

# for reproducible random result
set.seed(1)

# generate 1000 random integer values between 1 to 10 using round
x <- runif(1000, 1, 10)

# Create a histogram to visualize uniform distribution
library(ggplot2)  
ggplot() + aes(x)+ geom_histogram(color="darkblue", fill="lightblue") + 
    xlab("Random values") + 
    ylab("Frequency count") + 
    ggtitle("Uniform Distribution")

runif uniform distribution histogram

The above histogram visualizes the distribution of 1000 random numbers generated using the runif() function.

Related: random.uniform(): runif() Equivalent Function in Python

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