[R] select element from each row of the matrix

[David Winsemius]

On Jul 20, 2011, at 4:23 PM, gallon li wrote:

> I have a 5 column matrix like
>
> 12 10 8 6 3
> 10 9 8 7 5
> 14 NA 4 NA NA NA
> 15 NA 10 NA 5
> ...

Probably something along the lines of

aapply(mtx, 1, function(x) { c( x[ which(x <= 5)[1] ], # first row are  
the values
                                 which(x <= 5)[1])  } ) # second row  
the positions

-- 
David.

>
> I want to select the position of the first entry for each row <=5
>
> for example, for the first row, I want to select the last element  
> and return
> its position as 5;
> for th e third row, I want to select the third element and return its
> position as 3;
> similarly for the 4th row, I want to select the fifth element and  
> return its
> position 5.
>
> I am wondering how to do this fast? Thanks a lot!
>
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>
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David Winsemius, MD
West Hartford, CT