[R] GLM question

[Joshua Wiley]

Hi Andra,

There are several problems with what you are doing (by the way, I
point them out so you can learn and improve, not to be harsh or rude).
 The good news is there is a solution (#3) that is easier than what
you are doing right now!

1) glm.fit() is a function so it is a good idea not to use it as a variable

2) You are looping through your variables, when you could avoid the
loop and use:
  paste(x, collapse = " + ")

for example with the first ten letters of the alphabet:

> paste(LETTERS[1:10], collapse = " + ")
[1] "A + B + C + D + E + F + G + H + I + J"

3) If you store your data in a data frame like:

dat <- as.data.frame(cbind(Y = y, x))

you do not need to do anything other than:

glm(Y ~ ., data = dat, family = binomial)

because R will expand the "." to be every variable in the dataset that
is not the outcome.  This would be my recommendation.

4) If you really wanted to use your pasted string, try it like this:

f <- "mpg ~ hp" # create formula as string
lm(as.formula(f), data = mtcars) # convert to formula and use in model

although there are many variants of this some of which may be better.
Still, I would recommend #3 in your case over #4.

I hope this helps,

Josh

On Mon, Aug 22, 2011 at 9:43 PM, Andra Isan <andra_isan at yahoo.com> wrote:
> Hi All,
>
> I am trying to fit my data with glm model, my data is a matrix of size n*100. So, I have n rows and 100 columns and my vector y is of size n which contains the labels (0 or 1)
>
> My question is:
> instead of manually typing the model as
>  glm.fit = glm(y~ x[,1]+x[,2]+...+x[,100], family=binomial())
>
> I have a for loop as follows that concatenates the x variables as follows:
>
> final_str=NULL
> for (m in 1:100){
> str = paste(x[,m],+,sep="")
> final_str= paste(final_str,str,sep="")
> }
>
> glm.fit = flm(y~final_str,family=binomial())
> but final_str is treated as a string and it does not work. Could you please help me with fixing that?
>
> Thanks a lot,
> Andra
>
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-- 
Joshua Wiley
Ph.D. Student, Health Psychology
Programmer Analyst II, ATS Statistical Consulting Group
University of California, Los Angeles
https://joshuawiley.com/