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You can use the following syntax to calculate a conditional mean in R:

mean(df[df$team == 'A', 'points'])

This calculates the mean of the â€˜pointsâ€™ column for every row in the data frame where the â€˜teamâ€™ column is equal to â€˜A.â€™

The following examples show how to use this syntax in practice with the following data frame:

#create data frame df frame(team=c('A', 'A', 'A', 'B', 'B', 'B'), points=c(99, 90, 93, 86, 88, 82), assists=c(33, 28, 31, 39, 34, 30)) #view data frame df team points assists 1 A 99 33 2 A 90 28 3 A 93 31 4 B 86 39 5 B 88 34 6 B 82 30

**Example 1: Calculate Conditional Mean for Categorical Variable**

The following code shows how to calculate the mean of the â€˜pointsâ€™ column for only the rows in the data frame where the â€˜teamâ€™ column has a value of â€˜A.â€™

#calculate mean of 'points' column for rows where team equals 'A' mean(df[df$team == 'A', 'points']) [1] 94

The mean value in the â€˜pointsâ€™ column for the rows where â€˜teamâ€™ is equal to â€˜Aâ€™ is **94**.

We can manually verify this by calculating the average of the points values for only the rows where â€˜teamâ€™ is equal to â€˜Aâ€™:

- Average of Points: (99 + 90 + 93) / 3 =
**94**

**Example 2: Calculate Conditional Mean for Numeric Variable**

The following code shows how to calculate the mean of the â€˜assistsâ€™ column for only the rows in the data frame where the â€˜pointsâ€™ column has a value greater than or equal to 90.

#calculate mean of 'assists' column for rows where 'points' >= 90 mean(df[df$points >= 90, 'assists']) [1] 30.66667

The mean value in the â€˜assistsâ€™ column for the rows where â€˜pointsâ€™ is greater than or equal to 90 is **30.66667**.

We can manually verify this by calculating the average of the assists values for only the rows where points is greater than or equal to 90:

- Average of Assists: (33 + 28 + 31) / 3 =
**30.66667**

**Additional Resources**

The following tutorials explain how to calculate other mean values in R:

How to Calculate a Trimmed Mean in R

How to Calculate Geometric Mean in R

How to Calculate a Weighted Mean in R