[R] How to reference previous row?

[Carlos J. Gil Bellosta]

Hello,

The solution to problem will seem far easier if you think in a different
way. For instance, you may want to consider the extra dummy column

previous.first.value <- c( "NA", first[ - length(first) ] )

Then you can "horizontally" compare first with it's previous value.

Best regards,

Carlos J. Gil Bellosta
http://www.datanalytics.com


On Mon, 2009-01-12 at 18:57 +1100, Heston Capital wrote:
> I am trying to write some code where the factor references its
> previous value, but can't find a solution searching through the
> archive.
> 
> > X
>   first second	
> 1     A      1
> 2     A      2
> 3     B      3
> 4     B      4
> 5     B      5
> 6     C      6
> 7     C      7
> 
> I need a third column, in pseudo code-
>  If value of first=previous value of first:
> 	third=previous value of third
>  else third = second
> 
> So the third column would look like:
> 0
> 0
> 3
> 3
> 3
> 6
> 6
> 
> 
> Thanks!
> 
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