[R] sample unique pairs from a matrix

[jos matejus]

Dear All,

Many thanks for all your useful suggestions. Much appreciated.

Jos

2009/5/28 David Winsemius <dwinsemius at comcast.net>:
> Your last step will either be a single number (not really a sampling
> operation) or a
> non-positive number. So at best you really only have an number that depends
> entirely on the prior sequence of draws.
>
> --
> David.
>
> On May 28, 2009, at 8:21 AM, jos matejus wrote:
>
>> Dear Ritchie and David,
>>
>> Thanks very much for your advice. I had thought of this potential
>> solution, however it doesn't really fullfill my second criteria which
>> is that once a particular cell has been sampled, the row and column of
>> that cell can't be sampled from subsequently. In other words, the next
>> sample would be taken from a 5x5 matrix, and then a 4x4 matrix and so
>> on until I have my 6 values.
>>
>> I will keep thinking!
>> Cheers
>> Jos
>>
>> 2009/5/28 David Winsemius <dwinsemius at comcast.net>:
>>>
>>> On May 28, 2009, at 6:33 AM, jos matejus wrote:
>>>
>>>> Dear R users,
>>>>
>>>> I have a matrix of both negative and positive values that I would like
>>>> to randomly sample with the following 2 conditions:
>>>>
>>>> 1. only sample positive values
>>>> 2. once a cell in the matrix has been sampled the row and column of
>>>> that cell cannot be sampled from again.
>>>>
>>>> #some dummy data
>>>> set.seed(101)
>>>> dataf <- matrix(rnorm(36,1,2), nrow=6)
>>>>
>>>> I can do this quite simply if all the values are positive by using the
>>>> sample function without replacement on the column and row indices.
>>>>
>>>> samrow <- sample(6,replace=F)
>>>> samcol <- sample(6,replace=F)
>>>> values <- numeric(6)
>>>> for(i in 1:6){
>>>>       values[i] <- dataf[samrow[i], samcol[i]]
>>>> }
>>>>
>>>> However, I am not sure how to include the logical condition to only
>>>> include postitive values
>>>> Any help would be gratefully received.
>>>> Jos
>>>
>>>> M <- matrix(rnorm(36),nrow=6)
>>>
>>>> M[M[,]>0]
>>>
>>>  [1] 1.65619781 0.56182830 0.23812890 0.81493915 1.01279243 1.29188874
>>> 0.64252343 0.53748655 0.31503112
>>> [10] 0.37245358 0.07942883 0.56834586 0.62200056 0.39478167 0.02374574
>>> 0.04974857 0.56219171 0.52901658
>>>
>>>
>>>> sample(M[M[,]>0],6,replace=F)
>>>
>>> [1] 0.56834586 0.07942883 0.31503112 0.62200056 0.02374574 0.64252343
>>>
>>> --
>>> David Winsemius, MD
>>> Heritage Laboratories
>>> West Hartford, CT
>>>
>>>
>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
>