Marc Schwartz wrote:
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.
One other tweak here, if you use TRUE/FALSE rather than 1/0 to define
the positions and this gets rid of the need for 'vars':
bits <- c(TRUE, FALSE, TRUE, TRUE, FALSE)
> paste("X", which(bits), collapse = " + ", sep = ".")
[1] "X.1 + X.3 + X.4"
HTH,
Marc
______________________________________________
R-help@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.
