From: Marc Schwartz <marc_schwartz_at_comcast.net>

Date: Tue, 06 May 2008 14:18:34 -0500

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 06 May 2008 - 19:21:34 GMT

Date: Tue, 06 May 2008 14:18:34 -0500

Esmail Bonakdarian wrote:

> Hello,

*>
**> Still a newbie with R, though I have learned a lot from reading
**> this list. I'm hoping someone can help with this question:
**>
**> I have two vectors, one for variables, and one for bits.
**>
**> I want to build a string (really a formula) based on the values in my
**> vector of 1s and 0s in bits. If I have a one, I want to include the
**> corresponding entry in the vars vector, otherwise ignore it. Of course
**> the "bits" vector will not stay the same.
**>
**> So for example:
**>
**> vars=c('X.1', 'X.2', 'X.3', 'X.4', 'X.5')
**>
**> bits=c(1, 0, 1, 1, 0)
**> ones=which(bits==1)
**>
**> should yield:
**>
**> "X.1 + X.3 + X.4"
**>
**> where as
**>
**> bits=c(1, 1, 0, 0, 0)
**>
**> would yield
**>
**> "X.1 + X.2"
**>
**> the "which" operator gives me the index values, is there an easy and
**> *efficient* way to build this string so that I can pass it on to glm?
**> I can probably hack some ugly code together to do this, but it won't
**> be efficient, and it won't be elegant :-)
**>
**> Can anyone help?
**>
**> Thanks!
*

Depending upon other factors, there may be a better and more general approach to what you are trying to do relative to selecting subsets of IV's. However, given the information you have provided:

vars <- c('X.1', 'X.2', 'X.3', 'X.4', 'X.5') bits <- c(1, 0, 1, 1, 0)

> paste(vars[bits == 1], collapse = " + ") [1] "X.1 + X.3 + X.4"

bits <- c(1, 1, 0, 0, 0)

> paste(vars[bits == 1], collapse = " + ") [1] "X.1 + X.2"

You will then need to use as.formula() to coerce the resultant vectors before passing them to the model function.

**HTH,
**
Marc Schwartz

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 06 May 2008 - 19:21:34 GMT

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