Summary Statistics

Given a vector, we can find several quantities:

mean(x) finds the mean,
min(x) finds the minimum coordinate
max(x) finds the maximum coordinate
median(x) finds the median
var(x) finds the sample variance (divides over n-1).
range(x) finds the max(a)-min(a).
sum(x) finds the sum of all coordinates.
prod(x) finds the product of all coordinates
length(x) finds the number of coordinates
summary(x) finds the mean and the quartiles
quantile(x) finds the quartiles
quantile(x,p) finds the p-th quartiles, p is argument, between 0 and 1.

When there are missing values in the data, the functions max(), min(), range(), mean(), and median() return NA, and the functions var(), cor(), and quantile() return an error message. Using the command with the argument na.rm=T, forces Splus to remove any missing values from the vector x and to return the maximum value in x.

> x_c(1,2,3,3,3,4,7,8,9,NA)  
> max(x, na.rm=T)
[1] 9                         
> mean(x, na.rm=T)
[1]  4.444444
> var(x[!is.na(x)])
[1] 8.027778 
> y_c(1,2,3,4,5,6,7,8,9,10)
> cor(x[!is.na(x)],y[!is.na(x)]
[1] 0.9504597

We can find trimmed means. the argument trim takes any value between 0 and 0.5 inclusive to be trimmed from each end of the ordered data

       
> mean(x, trim=0.2, na.rm=T)
[1]  4.285714

The function quantile() returns the quantiles of x specified in the argument "probs"

  
> quantile(x, probs=c(0,0.1,0.9), na.rm=T)
  0% 10% 90%                  
   1 1.8 8.2

These functions may also be used on matrices; they will not be applied to the rows or columns individually but rather will find the max, min, etc. of the whole matrix