Re: [R] Random subset

From: Marc Schwartz <marc_schwartz_at_comcast.net>
Date: Wed, 30 Jul 2008 13:33:07 -0500

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



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