a vector or matrix of numerical values.
A character vector of three values: the minimum, the mean, the maximum.
On Aug 5, 2019, the dimension was dropped as the fourth column, and
this function returned to the original intention (revealed by its
name). Another change is that the function now returns numerical
results, leaving the task of setting the number of digits to
library(oce) threenum(1:10)#>  1.0 5.5 10.0