On 2010-09-18 13:14, Joshua Wiley wrote:
Hello Ben,
I believe the problem is not strictly update() in the for loop, but
the formula being passed to update(). The value of "i" changes, but
its symbol does not, so the second time through its like you overwrite
the first. Here is one way around it that works for me:
mdat<- matrix(c(1,2,3, 11,23,13, 12,4,8), nrow = 3, ncol=3, byrow=TRUE)
reg<- lm(mdat[7:9]~1)
for(i in 1:2) {
x<- paste(". ~ . + mdat[", ((i-1)*3 + 1), ":", (i * 3), "]", sep ="")
print(x) # just to see it
reg<- update(reg, x) #update reg twice
}
reg
I am guessing this is a simpler example of what you are really trying
to do, but ff you are not interested in doing anything with reg
between updates, you might consider just update()ing it once with the
full model.
Hope that helps,
Josh
P.S. I really tried to implement a suggestion for a better way to
create formulae by Douglas Bates (see
http://groups.google.com/group/ggplot2/msg/3169aee8708e5e0c? ), but
was spectacularly unsuccessful.
Ben is making strange use of mdat in lm(); I would use a data frame.
At least, we should name the columns.
mdat <- matrix(c(1,2,3, 11,23,13, 12,4,8),
nrow = 3, ncol=3, byrow=TRUE)
colnames(mdat) <- paste("x", 1:3, sep="")
dat <- as.data.frame(mdat)
Then see if the following gives a suitable hint:
reg <- lm(x3 ~ 1, data = dat) ## or: reg <- lm(mdat[,"x3"] ~ 1)
(fo <- formula(reg))
for(i in 1:2) {
x <- as.name(colnames(dat)[i])
fo <- update(fo, bquote(~ . + .(x)))
print(fo)
}
(using update.formula() as illustration)
-Peter Ehlers
On Sat, Sep 18, 2010 at 9:30 AM, Benjamin Godlove<bgodl...@oberlin.edu> wrote:
Hi,
First let me say I am a big fan of R and appreciate all your time and
effort.
The update() function does not seem to work in a for loop. Consider the
following:
mdat<- matrix(c(1,2,3, 11,23,13, 12,4,8), nrow = 3, ncol=3, byrow=TRUE)
reg<- lm(mdat[7:9]~1)
for(i in 1:2) {
reg<- update(reg,.~.+mdat[((i-1)*3 + 1):(i*3)]) #update reg twice
}
reg # reg should have two independent variables, but it only has one
The update() function in conjunction with a for loop will only consider the
last update, and not save all the previous ones. Is there a way around
this?
I appreciate your time.
- Ben Godlove
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