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?

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:

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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 –

- Create a dataframe (skip this step if you already have a dataframe on which you want to operate).
- Use the
`var()`

function to compute the variance of column values. Pass the column values vector as an argument. - 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.

You might also be interested in –

- How to Add a Column to a Dataframe in R?
- Rename Column Name in R Dataframe
- Select One or More Columns From R Dataframe

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