How to Use Mean() In R with Examples

mean() can be used to calculate mean in R. The following is the basic statement.

mean(x, trim = 0, na.rm = FALSE)

  • x: It is an R object. 
  • trim: It is in the range of (0 to 0.5). The number indicates the percentage of observations to be trimmed from each end of sorted x, before the mean is computed. The default value is 0.
  • na.rm: It is a logical value indicating whether NA values should be stripped before the computation proceeds. The default value is FALSE.

Example 1: Basic format

x <- c(4,5,8,44,32,22,45,3,8,99,100,120)
mean(x)

Output:

> x <- c(4,5,8,44,32,22,45,3,8,99,100,120)
> mean(x)
[1] 40.83333

Example 2: With trim

Example 2 shows how to use trim in mean(). trim will remove the percentage of observations on both ends in the sorted vector.

x <- c(4,5,8,44,32,22,45,3,8,99,100,120)
mean(x, trim=0.1)

Output:

> x <- c(4,5,8,44,32,22,45,3,8,99,100,120)
> mean(x, trim=0.1)
[1] 36.7

We can sort the vector and remove both end to see whether we can get the exactly same result.

# create a vector in R
x <- c(4,5,8,44,32,22,45,3,8,99,100,120)

# sort the vector
sort(x, decreasing = FALSE)

# calculate the number of the observations
print(length(x))

# calculate the number of observations we need to remove on both ends
print(length(x)*0.1)

Output:

> sort(x, decreasing = FALSE)
 [1]   3   4   5   8   8  22  32  44  45  99 100 120

> length(x)
[1] 12

> 12*0.1
[1] 1.2

Based on the output above, we know that we need to remove 1 observations (1.2 ≈ 1). Based on the sorted vector, we know that we need to remove 3 and 120 from both ends. Thus, we can manually calculate the mean to see whether we get the same mean of 36.7 shown above. 

# manually calculate the mean
(sum(x)-3-120)/10

Output:

> (sum(x)-3-120)/10
[1] 36.7

Example 3: with NA

The following vector has NA in the vector. We can see that the NA will make the mean as NA. 

x <- c(4,5,8,44,32,22,45,3,8,99,100,120,NA)
mean(x)

Output:

> x <- c(4,5,8,44,32,22,45,3,8,99,100,120,NA)
> mean(x)
[1] NA

# create a vector in R
x <- c(4,5,8,44,32,22,45,3,8,99,100,120,NA)

# add na.rm=TRUE in mean()
mean(x,na.rm = TRUE)

Output:

> x <- c(4,5,8,44,32,22,45,3,8,99,100,120,NA)
> mean(x,na.rm = TRUE)
[1] 40.83333

Further Reading