Hello,
Inline.
Em 14-10-2013 18:01, David C. Howell escreveu:
I am having difficulty extracting specific results from the model
object. The following code shows where I am stuck.
I want to run resamplings of a data set. For each I want to extract a
particular F for the contrasts. If I run a very simple model
(e.g. model1 <- aov(time~group) ) I can get the relevant coefficients,
for example, by using "model1$coefficients". That's fine. But I don't
want the coefficients of the model, I want the contrasts. So I tried
model2=summary(model1, split = list(group = list("1&3 vs 2"=1, "1 vs 3"
= 2)))
This gives me the printout summary table that I want. i.e.
model2
Df Sum Sq Mean Sq F value Pr(>F)
group 2 4090 2045 8.081 0.000682 ***
group: 1&3 vs 2 1 1483 1484 5.863 0.017988 *
group: 1 vs 3 1 2606 2606 10.300 0.001987 **
Residuals 72 18219 253
That's the summary table that I want, but I want to extract, for example
the F value of 5.863.
Looking at the structure of that object I get
str(model2)
List of 1
$ :Classes ‘anova’ and 'data.frame': 4 obs. of 5 variables:
..$ Df : Named num [1:4] 2 1 1 72
.. ..- attr(*, "names")= chr [1:4] "" "1&3 vs 2" "1 vs 3" ""
..$ Sum Sq : Named num [1:4] 4090 1483 2606 18219
.. ..- attr(*, "names")= chr [1:4] "" "1&3 vs 2" "1 vs 3" ""
..$ Mean Sq: Named num [1:4] 2045 1483 2606 253
.. ..- attr(*, "names")= chr [1:4] "" "1&3 vs 2" "1 vs 3" ""
..$ F value: Named num [1:4] 8.08 5.86 10.3 NA
.. ..- attr(*, "names")= chr [1:4] "" "1&3 vs 2" "1 vs 3" ""
..$ Pr(>F) : Named num [1:4] 0.000682 0.017988 0.001987 NA
What I would like to do is to request result$"F value[2]"
but that just gives "NULL."
I note that if I request the structure for model 1, the first element is
$Df.
No, it's not. The first element is a data.frame, whose 4th column is the
column you want. Using the first example in ?aov,
sm <- summary(aov(yield ~ block + N*P*K, npk))
sm[[1]]$`F value` # note the backticks
# equivalent
sm[[1]][[4]]
Hope this helps,
Rui Barradas
But when I ask for the structure of model2, the first element is
..$Df. I assume that those two dots represent an ellipsis, but nothing
is ?str, ?attr, or other help screens tell me how to interpret and use
..Df or any of the other elements.
Any help?
Thanks,
Dave Howell
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and provide commented, minimal, self-contained, reproducible code.
