[R] count value changes in a column [EDIT]

[Justin]

Justin Haynes <jtor14 <at> gmail.com> writes:

> 
> is there a way to look for value changes in a column?
> 
> df<-data.frame(state=sample(rep(1:5,200),1000))
> 
> any of the five states are acceptable.  however if, for example,
> states 4 or 5 follow state 3, i want to overwrite them with 3.
> changes from 1 to any value and 2 to any value are acceptable as are
> changes from any value to 1 or 2.
> 
> By way of an example:
> 
> the sequence 1 3 3 5 5 3 2 4 2 1 5 3 3 5
> 
> should read   1 3 3 3 3 3 2 4 2 1 5 5 5 5
> 

Additionally, can i count the number of times my vector changes to a number?  
in my previous example i would like to see
state count

1    2
2    2
3    1
4    1
5    1

> Thanks for the help!
> 
> Justin
> 
>