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Variance of Values in an R Column (Step by Step)

The R programming language comes with a number of helpful functions to work with the data stored in data structures like vectors, lists, dataframes, etc. In this tutorial, we will look at one such function that helps us get the variance of the values in a column of an R dataframe.

How to get the variance of values in an R dataframe column?

variance of a column in R

You can use the built-in var() function in R to compute the variance of values in a dataframe column. Pass the column values as an argument to the function.

The following is the syntax –

var(dataframe[[column_name]])

Pass na.rm=TRUE to avoid the NA values when computing the variance.

It returns the variance of the passed vector.

Steps to compute the variance of values in an R column

Let’s now look at a step-by-step example of using the above syntax to compute the variance of a numeric column in R.

Step 1 – Create a dataframe

First, we will create an R dataframe that we will be using throughout this tutorial.

# create a dataframe
employees_df = data.frame(
  "Name"= c("Jim", "Dwight", "Angela", "Tobi", "Kevin"),
  "Age"= c(26, 28, 29, 32, 30)
)
# display the dataframe
print(employees_df)

Output:

  Team_A Team_B
1     70     65
2     80     95
3     90     91

We now have a dataframe containing information about some employees in an office. The dataframe has two columns – “Name” and “Age”.

Step 2 – Calculate the variance of values in the column using the var() function

To calculate the variance of values in a column, pass the column values as an argument to the var() function. You can use the [[]] notation to access the values of a column.

Let’s compute the variance in the “Age” column.

# variance in "Age" column
var_age = var(employees_df[["Age"]])
# display the variance
print(var_age)

Output:

[1] 5

We get the variance in the “Age” column 5.

Variance of a column with NA values in R

What if there are NA values in a column?

Let’s find out.

# create a dataframe
employees_df = data.frame(
  "Name"= c("Jim", "Dwight", "Angela", "Tobi", "Kevin"),
  "Age"= c(26, 28, NA, 32, 30)
)
# display the dataframe
print(employees_df)

Output:

    Name Age
1    Jim  26
2 Dwight  28
3 Angela  NA
4   Tobi  32
5  Kevin  30

Here, we created a new dataframe such that the “Age” column now contains some NA values.

Now, let’s apply the var() function to the “Age” column.

# variance in "Age" column
var_age = var(employees_df[["Age"]])
# display the variance
print(var_age)

Output:

[1] NA

We get NA as the variance for the “Age” column. This happened because performing any mathematical operation with NA results in an NA in R.

If you want to compute the variance of a column with NA values, pass na.rm=TRUE to the var() function to skip the NA values when computing the variance.

# variance in "Age" column
var_age = var(employees_df[["Age"]], na.rm=TRUE)
# display the variance
print(var_age)

Output:

[1] 6.666667

We now get the variance of the “Age” column excluding the NA values.

Summary – Variance of Column Values in R

In this tutorial, we looked at how to compute the sum of values in a column of an R dataframe. The following is a short summary of the steps –

  1. Create a dataframe (skip this step if you already have a dataframe on which you want to operate).
  2. Use the var() function to compute the variance of column values. Pass the column values vector as an argument.
  3. If your column contains any NA values, pass na.rm=TRUE to the var() function to calculate the variance excluding the NA values in the column.

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Author

  • Piyush is a data scientist passionate about using data to understand things better and make informed decisions. In the past, he's worked as a Data Scientist for ZS and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.

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