[R] how to track a number in a row

[David Winsemius]

On Jan 11, 2010, at 10:16 PM, David Winsemius wrote:

>
> On Jan 11, 2010, at 9:38 PM, Márcio Resende wrote:
>
>>
>> Hi,
>> I have a 100x15 matrix and in each row a set of 15 random numbers  
>> out of 25.
>> for example:
>>
>> b <- c(1:25)
>> a <-matrix(0,10,15)
>> for (i in 1:10){
>> a[i,] <- sample(b,15,replace = FALSE)
>> }
>>
>> I would like to create another matrix (25x100), for example "d"  
>> with the
>> probability of each number from the first matrix
>> Therefore I need to track, for example, if number 1 is present in  
>> the first
>> row (d[1,1]) (which would give me an probability of 1 out of 1).
>> Then, track again if number 1 is present on the second row (d[2,1])  
>> (And if
>> not, the probability would be 1 out of 2 = 0.5)...and so on for all  
>> the 25
>> collumns (25 numbers) and all the 100 rows.
>>
>> Could anybody help how to do it??
>
> Maybe:
>
> > apply(a, 2, table)[[1]]
>
> 1  5  6  7 10 16 21 22 25
> 1  2  1  1  1  1  1  1  1
> > apply(a, 2, table)[[1]]/10
snipped out earlier intermediates

The reason the d matrix looks wrong is that I failed to "zero" it  
after an incorrect application of the loop logic. Ignore this column  
1. I think the "answer" will be what you asked for.

> > for(i in 1:15) {d[as.numeric(names(lapply(apply(a, 2, table), "/",  
> 10)[[i]])), i] <- lapply(apply(a, 2, table), "/", 10)[[i]]}
> > d
>      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]  
> [,13] [,14] [,15]
> [1,]  0.1  0.1  0.1  0.1  0.0  0.0  0.0  0.1  0.0   0.0   0.1    
> 0.1   0.1   0.0   0.0
> [2,]  0.1  0.1  0.1  0.0  0.1  0.0  0.0  0.0  0.0   0.0   0.1    
> 0.0   0.0   0.0   0.0
> [3,]  0.1  0.0  0.0  0.0  0.1  0.0  0.0  0.0  0.1   0.2   0.0    
> 0.1   0.0   0.0   0.0
> [4,]  0.1  0.0  0.0  0.2  0.0  0.0  0.2  0.0  0.0   0.0   0.0    
> 0.0   0.0   0.0   0.1
> [5,]  0.2  0.0  0.1  0.0  0.1  0.0  0.0  0.0  0.0   0.0   0.0    
> 0.0   0.0   0.0   0.3
snip
David Winsemius, MD
Heritage Laboratories
West Hartford, CT