sd, mean with a frequency distribution matrix

Hi,

  Just learned another way to calculate sd for a frequency distribution
matrix:

p <- matrix(c(10,3,20,4,30,5),ncol=2,byrow=TRUE)
p

[,1] [,2]
[1,]   10    3
[2,]   20    4
[3,]   30    5

rep(p[,1],p[,2])

[1] 10 10 10 20 20 20 20 30 30 30 30 30

sd(rep(p[,1],p[,2]))

[1] 8.348471



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