# how to exclude max and min when finding mean?

Hi. How to find the mean, median excluding the maximum and minimum variables from the given list (column) of numbers? Thanks.

Suppose the column of interest is named `t` in the data frame named `df`.

Then, one way of doing this will be `mean(x = sort(x = df\$t)[-c(1, length(x = df\$t))])`.

``````df <- data.frame(r = rnorm(n = 10),
s = rnorm(n = 10),
t = rnorm(n = 10))

df
#>              r          s           t
#> 1  -1.83591079 -0.1826240  1.45745501
#> 2   1.60511929 -0.7182501 -1.14194643
#> 3   0.39539556  0.3468794 -1.28876245
#> 4   2.25208190 -0.9199469 -2.22691378
#> 5   0.70405190  0.8550220  0.00532131
#> 6  -0.13380410  1.3264477  0.28501685
#> 7  -0.33047812  0.2084321  0.49404108
#> 8   1.34002246  1.4510729 -1.06143957
#> 9   0.47653311 -0.3784250  0.48697362
#> 10  0.03415973 -0.8906984  0.26499137

mean(x = sort(x = df\$t)[-c(1, length(x = df\$t))]) # what you want
#>  -0.2444755

mean(x = df\$t) # mean based on all observations
#>  -0.2725263
``````

Created on 2019-03-18 by the reprex package (v0.2.1)

Do you have any particular reason to remove just 1 observation from both sides instead of trimming a `p` proportion?

1 Like

For complementing Anirban´s answer, this would be a way to do it for all your variables at once

``````set.seed(123)
df <- data.frame(r = rnorm(n = 10),
s = rnorm(n = 10),
t = rnorm(n = 10))
library(dplyr)

df %>%
summarise_each(~ mean(.[!. %in% c(min(.), max(.))]))
#>            r         s          t
#> 1 0.03703159 0.2832405 -0.4765888
``````

Created on 2019-03-18 by the reprex package (v0.2.1)
Also, I agree with his observation about the use of a trimmed mean instead of this approach e.g. `mean(df\$t, trim = 0.10)`

2 Likes

thanks very much:) It works perfectly

Thank you. This way is far easier.

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