A trimmed mean is the mean of a dataset that has been calculated after removing a specific percentage of the smallest and largest values from the dataset.

For example, a 10% trimmed mean would represent the mean of a dataset after the 10% smallest values and 10% largest values have been removed.

The easiest way to calculate a trimmed mean in R is to use the following basic syntax:

#calculate 10% trimmed mean
mean(x, trim=0.1)

The following examples show how to use this function to calculate a trimmed mean in practice.

Example 1: Calculate Trimmed Mean of Vector

The following code shows how to calculate a 10% trimmed mean for a vector of data:

#define data
data = c(22, 25, 29, 11, 14, 18, 13, 13, 17, 11, 8, 8, 7, 12, 15, 6, 8, 7, 9, 12)

#calculate 10% trimmed mean
mean(data, trim=0.1)

[1] 12.375

The 10% trimmed mean is 12.375.

This is the mean of the dataset after the smallest 10% and largest 10% of values have been removed from the dataset.

Example 2: Calculate Trimmed Mean of Column in Data Frame

The following code shows how to calculate a 5% trimmed mean for a specific column in a data frame:

#create data frame
df = data.frame(points=c(25, 12, 15, 14, 19, 23, 25, 29),
                assists=c(5, 7, 7, 9, 12, 9, 9, 4),
                rebounds=c(11, 8, 10, 6, 6, 5, 9, 12))

#calculate 5% trimmed mean of points
mean(df$points, trim=0.05)

[1] 20.25

The 5% trimmed mean of the values in the ‘points’ column is 20.25.

This is the mean of the ‘points’ column after the smallest 5% and largest 5% of values have been removed.

Example 3: Calculate Trimmed Mean of Multiple Columns

The following code shows how to calculate a 5% trimmed mean for multiple columns in a data frame:

#create data frame
df = data.frame(points=c(25, 12, 15, 14, 19, 23, 25, 29),
                assists=c(5, 7, 7, 9, 12, 9, 9, 4),
                rebounds=c(11, 8, 10, 6, 6, 5, 9, 12))

#calculate 5% trimmed mean of points and assists
sapply(df[c('points', 'assists')], function(x) mean(x, trim=0.05))

 points assists 
  20.25    7.75 

From the output we can see:

• The 5% trimmed mean of the ‘points’ column is 20.25.
• The 5% trimmed mean of the ‘assists’ column is 7.75.

The following tutorials provide additional information about trimmed means: