On Wed, Jan 26, 2011 at 2:04 PM, Paul Bailey pdbai...@umd.edu wrote:
I'm having a problem with aggregate.formula when I call it in a function and
the function is converted from a string in the funtion
I think my problem may also only occur when the left hand side of the formula
is cbind(...)
Here is example code that generates a dataset and then the error.
The first function agg2 fails
agg2(FALSE)
do agg 2
Error in m[[2L]][[2L]] : object of type 'symbol' is not subsettable
but, if I run it have it return what it is going to pass to aggregate and
pass it myself, it works. I can use this for a workaround (agg3) where one
function does this itself.
I'm confused by the behavior. Is there some way to not have to use a separate
function to make the call ?
==
# start R code
# idea: in a function, count the number of instances
# of some factor (y) associated with another
# factor (x). aggregate.formula appears to be
# able to do this... but I have a problem if all of the following:
# (1) It is called in a function
# (2) the formula is created using as.formula(character)
# calling aggregate with the same formula (created with as.formula)
# outside the function works fine.
agg2 - function(test=FALSE) {
# create a factor y
dat - data.frame(y=sample(LETTERS[1:3],100,replace=TRUE))
# create a factor x
dat$x - sample(letters[1:4],100,replace=TRUE)
# make a column of 1s and zeros
# 1 when that row has that level of y
# 0 otherwise
lvls - levels(dat$y)
dat$ya - 1*(dat[,1] == lvls[1])
dat$yb - 1*(dat[,1] == lvls[2])
dat$yc - 1*(dat[,1] == lvls[3])
# this works fine if you give the exact function
agg1 - aggregate(cbind(ya,yb,yc)~x,data=dat,sum)
# and fine if you accept
fo - as.formula(cbind(ya,yb,yc)~x)
if(test) {
return(list(fo=fo,data=dat))
}
cat(do agg 2\n)
agg2 - aggregate(fo,data=dat,sum)
list(agg1,agg2)
}
agg2(FALSE)
ag - agg2(TRUE)
ag$fo
aggregate(ag$fo,ag$data,sum)
agg3 - function() {
ag - agg2(TRUE)
ag$fo
aggregate(ag$fo,ag$data,sum)
}
agg3()
# end R code
==
Paul Bailey
University of Maryland
The problem is that the aggregate statement:
agg2 - aggregate(fo, data = dat, sum)
is using non-standard evaluation and is literally looking at fo rather
than fo's value. This may be a bug in aggregate.formula but at any
rate you could try replacing that statement with the following to
force fo to be evaluated:
agg2 - do.call(aggregate, list(fo, data = dat, FUN = sum))
--
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