Randomly remove condition-selected rows from a matrix

I believe this does what you want:

m[-sample(which(m[,1]<8 & m[,2]>12),2),]

Analysis:

Get a boolean vector of rows fitting criteria:
    m[,1]<8 & m[,2]>12

What are their indexes?
    which(...)

Choose two among those indexes:
     sample(...,2)

Choose all except the selected rows from the original:
     m[- ... , ]

          -s

On Tue, Dec 30, 2008 at 9:59 AM, Guillaume Chapron

m <- matrix(1:20, nrow = 10, ncol = 2)
        [,1] [,2]
 [1,]    1   11
 [2,]    2   12
 [3,]    3   13
 [4,]    4   14
 [5,]    5   15
 [6,]    6   16
 [7,]    7   17
 [8,]    8   18
 [9,]    9   19
[10,]   10   20

Then, I want to remove randomly 2 rows among the ones where m[,1]<8 and
m[,2]>12