[R] Re turn values < 0 from Matrix

[David Winsemius]

I still remember my public spanking from Ben Bolker on the unnecessary  
use of "which" in this instance.

 > MM <- matrix(c(1:10,sample(-10:10,10)),nrow=10)
 > MM
       [,1] [,2]
  [1,]    1   -1
  [2,]    2    5
  [3,]    3   -2
  [4,]    4   -3
  [5,]    5    0
  [6,]    6    7
  [7,]    7   -9
  [8,]    8    1
  [9,]    9    6
[10,]   10    4

 > MM[MM[,2]<0, ]
      [,1] [,2]
[1,]    1   -1
[2,]    3   -2
[3,]    4   -3
[4,]    7   -9

 > MM[MM[,2]>0, ]
      [,1] [,2]
[1,]    2    5
[2,]    6    7
[3,]    8    1
[4,]    9    6
[5,]   10    4

-- 
David Winsemius
On Feb 9, 2009, at 9:46 AM, Ian Fiske wrote:

>
> If your matrix is called mat, how about
>
> mat[which(mat[,2] > 0), ]
>
>
> mat[which(mat[,2] < 0), ]
>
>
> -Ian
>
>
> mentor_ wrote:
>>
>> Hi,
>>
>> I have a matrix with negative and positiv values.
>> How can I get either the negative or positive values from the matrix?
>>
>> Matrix:
>>     [,1] [,2]
>> [1,]    1   -3
>> [2,]    2   -2
>> [3,]    3    5
>> [4,]    4   -2
>> [5,]    5    9
>> [6,]    6    8
>> [7,]    7   -2
>>
>> What I want to have is:
>>
>>     [,1] [,2]
>> [1,]    1   -3
>> [2,]    2   -2
>> [3,]    4   -2
>> [4,]    7   -2
>>
>> and:
>>
>>     [,1] [,2]
>> [1,]    3    5
>> [2,]    5    9
>> [3,]    6    8
>>
>>
>> Regards
>>
>
> -- 
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