# How to Find Standard deviation in R [Using Real-life DataSet]

The standard deviation is a measure that tells you how spread out data are in a dataset. It is a measurement of the dispersion of the values.

Picture this: You and your friends live near each other and daily walk to the school. If you count the total number of steps you and your friend take, it will be roughly the same, and the standard deviation will be low because you both live near each other. If there is a huge difference between you and your friend’s steps, then that means the standard deviation is high.

If the standard deviation is higher, then the spread of values is wider.

If the standard deviation is lower, then the spread of values is narrower.

It shows the central tendency, which is helpful in any type of data analysis.

To calculate the standard deviation in R language, use the “sd()” function.

## Syntax

``sd(x, na.rm = FALSE)``

## Parameters

 Name Description x It could be a vector of numbers or a column from a data frame. na.rm It stands for NA remove. If FALSE, NA values will be included in the calculation. If TRUE, NA values won’t be included in the calculation.

## Return value

The sd() function returns a numeric value representing the standard deviation.

## Example 1: Finding the standard deviation of a numeric vector

The above figure shows the standard deviation of a vector containing five elements.

``````# Create a numeric vector using c() function
vec <- c(11, 21, 19, 46, 50)

# Find the standard deviation of the vector using sd() function
stddev <- sd(vec)

# Print the standard deviation using the print() function
print(stddev)``````

Output

``[1] 17.4442``

## Example 2: Using Array

In the above figure, we found the sd of an array.

``````rv <- c(19, 21)
rv2 <- c(46, 4)

arr <- array(c(rv, rv2), dim = c(2, 2, 2))

cat("The standard deviation of array is", "\n")

sd(arr)``````

Output

``````The standard deviation of array is
[1] 16.11565``````

## Example 3: Using Matrix

In the above figure, we are finding the sd of the whole matrix.

``````mat <- matrix(1:9, ncol = 3)

sd(mat)
``````

Output

``````[1] 2.738613
``````

To calculate the standard deviation of each column, you need to use the “apply()” function in combination with the sd() function.

In the above figure, we calculated the standard deviation of each matrix column.

``````mat <- matrix(1:9, ncol = 3)

apply(mat, 2, sd)``````

Output

``````[1] 1 1 1
``````

## Example 4: Handling NA values

Pass the na.rm = TRUE argument within the sd() function to handle NA values in the data frame. This argument tells R to remove NA values before performing the calculation.

``````df <- data.frame(
col1 = c(1, NA, 3),
col2 = c(NA, 5, 6),
col3 = c(7, 8, NA)
)

sds <- apply(df, 2, sd, na.rm = TRUE)

sds
``````

Output

``````  col1       col2       col3
1.4142136  0.7071068   0.7071068
``````

## Example 5: Using Real Dataset with Visualization

Use the read_csv() method to import the real-world dataset in R.

For this tutorial, we will use Kaggle’s StudentPerformance.csv file as a dataset and find the standard deviation of the “math score” column.

### Step 1: Install the required libraries

You need to install tidyverse and ggplot2 libraries if you have not already!

``````install.packages("tidyverse")

install.packages("ggplot2")``````

### Step 2: Load the dataset

``````library(tidyverse)
library(ggplot2)

data <- read_csv("./DataSets/StudentsPerformance.csv")

head(data)``````

### Step 3: Finding Standard Deviation

Let’s focus on the “math score” column for understanding standard deviation.

``````# Using built-in R function for verification
std_dev <- sd(data\$`math score`)

print(std_dev)
``````

Output

``````[1] 15.16308
``````

### Step 4: Visualization

We will create a histogram to visualize the distribution of math scores.

On top of this histogram, we will overlay vertical lines to represent the mean and the standard deviations.

``````# Plot histogram
p <- ggplot(data, aes(x = `math score`))
+ geom_histogram(aes(y = ..density..),
binwidth = 5,
fill = "blue", alpha = 0.7
)
+ geom_density(alpha = 0.2, color = "red") + # Adding a density plot
# Add vertical line for mean
geom_vline(aes(xintercept = mean_math),
color = "green", linetype = "dashed", size = 1
) +

# Add vertical lines for standard deviations
geom_vline(aes(xintercept = (mean_math - std_dev_math_builtin)),
color = "purple", linetype = "dotted", size = 0.8
) +
geom_vline(aes(xintercept = (mean_math + std_dev_math_builtin)),
color = "purple", linetype = "dotted", size = 0.8
) +
geom_vline(aes(xintercept = (mean_math - 2 * std_dev_math_builtin)),
color = "orange", linetype = "dotted", size = 0.8
) +
geom_vline(aes(xintercept = (mean_math + 2 * std_dev_math_builtin)),
color = "orange", linetype = "dotted", size = 0.8
) +
geom_vline(aes(xintercept = (mean_math - 3 * std_dev_math_builtin)),
color = "yellow", linetype = "dotted", size = 0.8
) +
geom_vline(aes(xintercept = (mean_math + 3 * std_dev_math_builtin)),
color = "yellow", linetype = "dotted", size = 0.8
) +

# Add labels and title
labs(
title = "Distribution of Math Scores with Mean & Standard Deviations",
x = "Math Score", y = "Density"
) +
theme_minimal()

# Display the plot
p``````

Output

The green dashed line represents the mean.

The purple, orange, and yellow dotted lines represent 1, 2, and 3 standard deviations away from the mean, respectively.