R help - May 2005 - loop

Rather than using a loop, how can I remove all consequentially
repeated values as in this example?
I am guessing using diff would help but not quite sure how.
> get
> s
        date          f  
1 1999-01-01 1
2 1999-01-02 1
3 1999-01-03 1
4 1999-01-04 2
5 1999-01-05 2
> v <- s[1,'f']; for (i in 2:nrow(s)) { if (s[i,'f'] == v)
s[i,'f'] <- NA else v <- s[i,'f'] }
> s <- s[!is.na(s$f),]
> s
        date          f
1 1999-01-01 1
4 1999-01-04 2

On Wed, 18 May 2005, Omar Lakkis wrote:
> Rather than using a loop, how can I remove all consequentially
> repeated values as in this example?
> I am guessing using diff would help but not quite sure how.
>
>> get
>> s
>        date          f
> 1 1999-01-01 1
> 2 1999-01-02 1
> 3 1999-01-03 1
> 4 1999-01-04 2
> 5 1999-01-05 2
>
>> v <- s[1,'f']; for (i in 2:nrow(s)) { if (s[i,'f']
== v) s[i,'f'] <- NA else v <- s[i,'f'] }
>> s <- s[!is.na(s$f),]
>> s
>        date          f
> 1 1999-01-01 1
> 4 1999-01-04 2
I am not sure I see the pattern, but it might be one of

s[!duplicated(s$f), ]

s[diff(c(0, s$f)) != 0, ]

(which differ).

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
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