Did you look at the help? ?formula has a whole section about why
formulas have environments and what they do.
On Fri, 4 Feb 2011, Aviad Klein wrote:
# Hi all,
# I've made a function to make a formula out of a data.frame without columns
which contain a constant value.
# The function "which.constant" returns the indices of colums with constant
values:
which.constant <- function(data.frame) { # counts the number of columns in a
data.frame which are constant
h <- sapply(sapply(data.frame,unique),length) # count unique values
return(as.numeric(which(h==1)))}
# The function "make.formula" returns the desired formula but with an
unwanted addition :
make.formula <- function(data.frame) {
h <- which.constant(data.frame)
hh <- names(data.frame)[-h]
hh <- paste("~",paste(hh,collapse="+"),sep="")
return(as.formula(hh))}
# The following structure should give an example of how it works:
Data <- structure(list(cs_jail_2 = c(2L, 1L, 1L, 0L, 0L, 1L), cs_jail_3 =
c(0L,
0L, 0L, 0L, 0L, 0L), cs_jail_4 = c(1L, 2L, 2L, 2L, 0L, 0L)), .Names =
c("cs_jail_2",
"cs_jail_3", "cs_jail_4"), row.names = c(NA, 6L), class = "data.frame")
make.formula(Data)
# ~cs_jail_2 + cs_jail_4
# <environment: 0x0000000007654058>
# what does this <environment ...> mean?
# does it effect computation in any way? how to get read of it?
See also ?environment for how to remove (sic) it.
# thank you,
# Aviad
# aviadklein.wordpress.com/
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--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
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