# [R] Can the by() function return a single column?

David Winsemius dwinsemius at comcast.net
Wed Dec 15 19:43:38 CET 2010

```On Dec 15, 2010, at 11:19 AM, Gerrit Eichner wrote:

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

THere is also the scale function which can be called with the
parameters set to center but not scale the results:

with( test.df, ave( vector, factor, FUN=scale, scale=FALSE))  #
center=TRUE is default.

--
David.
>
> -- 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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>> and provide commented, minimal, self-contained, reproducible code.
>
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