R help - Oct 2008 - subsetting dataframe by rownames to be excluded

Is there a way to select a subset of a dataframe consisting of all  
those rows with rownames *except* from a subset of rownames to be  
excluded?  Example:

 > a <- data.frame(x=1:10,y=10:1)
 > a <- a[order(a$y),] # to make rownames differ visually

 > a[8,]
   x y
3 3 8

 > a["8",]
   x y
8 8 3

 > a[-8,]
     x  y
10 10  1
9   9  2
8   8  3
7   7  4
6   6  5
5   5  6
4   4  7
2   2  9
1   1 10

 > a[-"8",]
Error in -"8" : invalid argument to unary operator

-- is there a similar exclusion operator or simple way?  So far the  
best I can do is

 > a[setdiff(rownames(a),"8"),]
     x  y
10 10  1
9   9  2
7   7  4
6   6  5
5   5  6
4   4  7
3   3  8
2   2  9
1   1 10

Cheers,
Alexy

On Sat, 11 Oct 2008, Alexy Khrabrov wrote:
> Is there a way to select a subset of a dataframe consisting of all those
rows
> with rownames *except* from a subset of rownames to be excluded?  Example:
Yes: DF[is.na(match(row.names(DF), exclude_me)), ]
>
>> a <- data.frame(x=1:10,y=10:1)
>> a <- a[order(a$y),] # to make rownames differ visually
>
>> a[8,]
> x y
> 3 3 8
>
>> a["8",]
> x y
> 8 8 3
>
>> a[-8,]
>   x  y
> 10 10  1
> 9   9  2
> 8   8  3
> 7   7  4
> 6   6  5
> 5   5  6
> 4   4  7
> 2   2  9
> 1   1 10
>
>> a[-"8",]
> Error in -"8" : invalid argument to unary operator
>
> -- is there a similar exclusion operator or simple way?  So far the best I 
> can do is
>
>> a[setdiff(rownames(a),"8"),]
>   x  y
> 10 10  1
> 9   9  2
> 7   7  4
> 6   6  5
> 5   5  6
> 4   4  7
> 3   3  8
> 2   2  9
> 1   1 10
>
> Cheers,
> Alexy
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

Prof Brian Ripley <ripley <at> stats.ox.ac.uk> writes:
> Yes: DF[is.na(match(row.names(DF), exclude_me)), ]
Assuming everything is possible in R: would it be possible to make the below
work without breaking existing code?


a <- data.frame(x=1:10)
rownames(a) = letters[1:10]
exclude = c("a","c")
a[is.na(match(row.names(a), exclude)), ] # not really that easy to remember

a[-c(1,3),]
# In analogy....
a[-c(exclude),]   #invalid argument to unary operator
 

Dieter