R help - Feb 2011 - how to read the "Sum Sq" - column from summary.aov()

Dear R-Users,

I have a trivial problem, but extensive googling and ??'ing did not solve
it: I want to obtain the sums of squares from a summary.aov() object for later
use. Example:
> DV <- rnorm(100)
> IV1 <- as.factor(rep(c("male", "female"), times =
50))
> IV2 <- as.factor(rep(c("young", "old"), times = 50))
> 
> summary(aov(DV ~ IV1 * IV2))
            Df Sum Sq Mean Sq F value Pr(>F)
IV1          1  0.215 0.21499  0.2277 0.6343
Residuals   98 92.523 0.94411               

How can I store the sums of squares in a variable for later use? Like this:
>some.magic.command()
[1]  0.215  92.523

Thank you,
Bertolt

-- 
Dr. Bertolt Meyer
Senior research and teaching associate
Social Psychology, Institute of Psychology, University of Zurich
Binzmuehlestrasse 14, Box 15
CH-8050 Zurich
Switzerland

bmeyer at sozpsy.uzh.ch

On 2011-02-03 04:30, Bertolt Meyer wrote:
> Dear R-Users,
>
> I have a trivial problem, but extensive googling and ??'ing did not
solve it: I want to obtain the sums of squares from a summary.aov() object for
later use. Example:
>
>> DV<- rnorm(100)
>> IV1<- as.factor(rep(c("male", "female"), times =
50))
>> IV2<- as.factor(rep(c("young", "old"), times =
50))
>>
>> summary(aov(DV ~ IV1 * IV2))
>
>              Df Sum Sq Mean Sq F value Pr(>F)
> IV1          1  0.215 0.21499  0.2277 0.6343
> Residuals   98 92.523 0.94411
>
> How can I store the sums of squares in a variable for later use? Like this:
>
>> some.magic.command()
> [1]  0.215  92.523
str() is your friend.

  str( summary(aov(DV ~ IV1 * IV2)) )

shows that the summary is a list containing a data.frame.
Use

  summary(aov(DV ~ IV1 * IV2))[[1]]

to extract the data.frame and any one of

  summary(aov(DV ~ IV1 * IV2))[[1]][, 2]
  summary(aov(DV ~ IV1 * IV2))[[1]][, 'Sum Sq']
  summary(aov(DV ~ IV1 * IV2))[[1]]$'Sum Sq'

to extract the sum-of-squares vector.

Peter Ehlers
>
> Thank you,
> Bertolt
>

Hi,

If you do
test <- summary(aov(DV ~ IV1 * IV2))
str(test)
you will see that
test[[1]][2]
gives you what you want.

Reading more on indexing will also probably help you. str() is a very 
useful function, to use without moderation!

HTH,
Ivan

Le 2/3/2011 13:30, Bertolt Meyer a ?crit :
> summary(aov(DV ~ IV1 * IV2))
-- 
Ivan CALANDRA
PhD Student
University of Hamburg
Biozentrum Grindel und Zoologisches Museum
Abt. S?ugetiere
Martin-Luther-King-Platz 3
D-20146 Hamburg, GERMANY
+49(0)40 42838 6231
ivan.calandra at uni-hamburg.de

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