[R] modifying patterns in a matrix

[David Winsemius]

On Sep 17, 2008, at 3:50 PM, Stacey Burrows wrote:

> Dear R-users,
>
> I have some very simple data where 1's represent events and zeroes  
> non-events, e.g.
> temp <- rbind(c(0,1,0,0,1,1,1,0), c(0,0,0,1,0,0,0,0))
>
> For each row in the matrix, I would like to replace a singelton  
> event by a 0. That is, any 1 surrounded by zeroes (010) should be  
> replaced by a zero (000). Sequences of 1's should be left unchanged.
>
> So the modified matrix shoud look like this:
> 00001110
> 00000000

I had some success in identifying the non-singletons using filter(x,  
c(1,1,1) and applying a test for that value being greater than 1. You  
would need to disambiguate  what should be happening at the end of the  
series since filter() would be NA there. Adding 0 to a logical vector  
returns 0's and 1's

 > t(apply(temp,1, function(x) filter(x, c(1,1,1)) ) )
      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
[1,]   NA    1    1    1    2    3    2   NA
[2,]   NA    0    1    1    1    0    0   NA

  t(apply(temp,1, function(x) (filter(x, c(1,1,1)) >1)+0 ) )
      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
[1,]   NA    0    0    0    1    1    1   NA
[2,]   NA    0    0    0    0    0    0   NA

-- 
David Winsemius


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