R help - Dec 2010 - Can the by() function return a single column?

I would like to de-mean the 'vector' column of the following dataframe
by
factor:

set.seed(5444)
vector	<- rnorm(1:10)
factor	<- rep(1:2,5)
test.df	<- data.frame(factor, vector)

which is:

   factor     vector
1       1 -0.4963935
2       2 -2.0768182
3       1 -1.5822224
4       2  0.8025474
5       1  0.3504199
6       2  0.2358464
7       1 -0.3989443
8       2 -0.3692544
9       1 -0.3174586
10      2  1.4305431

Using the by() command, I get:
> by(test.df$vector, test.df$factor, function(x) {x - mean(x)})
test.df$factor: 1
[1] -0.007473699 -1.093302612  0.839339673  0.089975488  0.171461151
--------------------------------------------------------------------------------------------------
test.df$factor: 2
[1] -2.0813911  0.7979745  0.2312735 -0.3738272 
1.4259702
> 
My question is: Is there a way to have this output put back to the
dataframe? I.e to make by(), or some other command, return me a vector of
length 10 whose values x' correspond to x'_1 = x_1 - mean(x | factor1),
x'_2
= x_2 - mean(x | factor2),...

Thanks in advance for the help, and apologies for the poor notation. 

Vassilis

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Hello, Vassilis,

maybe
> with( test.df, ave( vector, factor, FUN = function( x) x - mean( x)))
does what you want.


-- Gerrit


On Wed, 15 Dec 2010, Vassilis wrote:
>
> I would like to de-mean the 'vector' column of the following
dataframe by
> factor:
>
> set.seed(5444)
> vector	<- rnorm(1:10)
> factor	<- rep(1:2,5)
> test.df	<- data.frame(factor, vector)
>
> which is:
>
>   factor     vector
> 1       1 -0.4963935
> 2       2 -2.0768182
> 3       1 -1.5822224
> 4       2  0.8025474
> 5       1  0.3504199
> 6       2  0.2358464
> 7       1 -0.3989443
> 8       2 -0.3692544
> 9       1 -0.3174586
> 10      2  1.4305431
>
> Using the by() command, I get:
>
>> by(test.df$vector, test.df$factor, function(x) {x - mean(x)})
> test.df$factor: 1
> [1] -0.007473699 -1.093302612  0.839339673  0.089975488  0.171461151
>
--------------------------------------------------------------------------------------------------
> test.df$factor: 2
> [1] -2.0813911  0.7979745  0.2312735 -0.3738272  1.4259702
>>
>
> My question is: Is there a way to have this output put back to the
> dataframe? I.e to make by(), or some other command, return me a vector of
> length 10 whose values x' correspond to x'_1 = x_1 - mean(x |
factor1), x'_2
> = x_2 - mean(x | factor2),...
>
> Thanks in advance for the help, and apologies for the poor notation.
>
> Vassilis
>
> -- 
> View this message in context:
http://r.789695.n4.nabble.com/Can-the-by-function-return-a-single-column-tp3089231p3089231.html
> Sent from the R help mailing list archive at Nabble.com.
>
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.

Hi Gerrit, 

This does exactly what I want, thank you very much! 

Even more, I notice that ave() uses the split/unsplit functions under the
hood, which are very useful tools as they allow to apply even more
complicated functions on a factor-by-factor basis. 

best,

Vassilis
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