[R] Random subset

[Marc Schwartz]

on 07/30/2008 01:28 PM Marc Schwartz wrote:
> on 07/30/2008 01:18 PM Alessandro wrote:
>> Hi all,
>>  
>> I wish to do a random subset (i.e. 200 or 300 points) from a dataset, 
>> but I
>> don't find the right code in R.
> 
> 
> See ?sample.
> 
> Randomly select 10 elements from a 30 element vector:
> 
> Vec <- 1:30
> 
>  > sample(Vec, 10)
>  [1] 16  5 10 29 27 30 21  1 12 28
> 
> 
> Randomly select 5 rows from a 10 row matrix:
> 
> MAT <- matrix(1:20, 10, 2)
> 
>  > MAT
>       [,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
> 
> 
>  > MAT[sample(5), ]
>      [,1] [,2]
> [1,]    5   15
> [2,]    3   13
> [3,]    4   14
> [4,]    1   11
> [5,]    2   12


Sorry, correction, that should be:

 > MAT[sample(10, 5), ]
      [,1] [,2]
[1,]    8   18
[2,]   10   20
[3,]    1   11
[4,]    6   16
[5,]    3   13


Fingers too fast there...

Marc