# [R] means and variances of several groups in the matrix

kathie kathryn.lord2000 at gmail.com
Mon Apr 21 09:03:30 CEST 2008

```Dear R users,

I have 32 observations in data x.  After sorting this, I want to compute
means and variances of 3 groups divided by "nr".

Actually, the number of groups is flexible.  Any suggestion will be greatly
appreciated.

Kathryn Lord

---------------------------------------------------------------------------
x=rnorm(32)
y=sort(x)

nr=matrix(c(12,11,10,10,10,11),2,3)
> nr
[,1] [,2] [,3]
[1,]   12   10   10    -> sum=32
[2,]   11   10   11    -> sum=32

For the 1st row in "nr", index of y = (1,..,12,   13,...,23,   24,...32)

I want to compute means and variances for 3 groups

(1st group is 1 through 12; 2nd group is 13-23; 3rd group is 24-32)

For the 2nd row in "nr", index of y = (1,..,11,   12,...,22,   23,...32)

also, I want to compute means and variances for 3 groups

(1st group is 1 through 11; 2nd group is 12-22; 3rd group is 23-32)

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