On Oct 22, 2010, at 12:17 PM, William Dunlap wrote:
-----Original Message-----
From: r-help-boun...@r-project.org
[mailto:r-help-boun...@r-project.org] On Behalf Of David Winsemius
Sent: Friday, October 22, 2010 6:25 AM
To: Dimitri Liakhovitski
Cc: r-help
Subject: Re: [R] lm looking for weights outside of the
user-defined function
On Oct 22, 2010, at 9:18 AM, Dimitri Liakhovitski wrote:
David,
I undersand - and I am sure what you are suggesting should
work. But I
just can't understand why it's not grabbing things INSIDE the
environment of the formula first.
I am not sure that either one of us understand what is meant by "the
environment of the formula".
"The environment of the formula" is the output of
environment(formula)
which is assigned to the current environment when the
formula is created. The modelling functions look for
variables (in the formula, weights, and subset arguments)
in the order
1) the data argument (usually an environment or a list)
2) environment of the formula
When an environment is searched for a name, the search
continues through all ancestral environments until the
name is found or until you run out of ancestors.
You can reassign the environment of a formula. E.g.,
compare the following two:
wr0 <- function(formula, MyData, WeightsVector) {
+ lm(formula, data=MyData, weights=WeightsVector)
+ }
wr1 <- function(formula, MyData, WeightsVector) {
+ environment(formula) <- environment()
+ lm(formula, data=MyData, weights=WeightsVector)
+ }
wr0(mpg~cyl, MyData=mtcars, WeightsVector=sqrt(1:32))
Error in eval(expr, envir, enclos) : object 'WeightsVector' not found
The wr0 call created a formula but the weights vector was "outside"
that environment? And that wss because the formula creation was at the
stage of evaluation the function arguments when tehy wouldn't "see"
each other? Except this works:
> xtoy <- function(x = 1:2, y=x){y}
> xtoy()
[1] 1 2
I'm trying to figure out what makes the wr0 version fail and that
xtoy() function succeed.
--
David.
wr1(mpg~cyl, MyData=mtcars, WeightsVector=sqrt(1:32))
Call:
lm(formula = formula, data = MyData, weights = WeightsVector)
Coefficients:
(Intercept) cyl
38.567 -2.966
Reassigning the environment can lead to the sort of
surprises that dynamic scoping gives you.
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
I've already tried to define the weights outside of the
function - and
it finds them.
But shouldn't it go in this order?
1. Look in the data frame
2. Look in the environment of the user-defined function
3. Look outside.
Hey, I only work here, I don't make the rules, I just follow them. I
agree that one might guess that to be the search order, but
it is not
what is documented.
--
David Winsemius, MD
West Hartford, CT
Dimitri
On Fri, Oct 22, 2010 at 9:15 AM, David Winsemius
<dwinsem...@comcast.net
wrote:
On Oct 22, 2010, at 9:01 AM, Dimitri Liakhovitski wrote:
Dear R'ers,
I am fighting with a problem that is driving me crazy. I
use "lm" in
my user-defined function, but it seems to be looking for weights
outside of my function's environment:
### Generating example data:
x<-data.frame(y=rnorm(100,0,1),a=rnorm(100,1,1),b=rnorm(100,2,1))
myweights<-runif(100)
data.for.regression<-x[1:3]
### Creating function "weighted.reg":
weighted.reg=function(formula, MyData, filename,WeightsVector)
{
print(dim(MyData))
print(filename)
print(length(WeightsVector))
regr.f<-
lm(formula,MyData,weights=WeightsVector,na.action=na.omit)
results<-as.data.frame(round(summary(regr.f)$coeff,3))
write.csv(results,file=filename)
return(results)
}
### Running "weighted.reg" with my data:
reg2<-weighted.reg(y~., MyData=x, WeightsVector=myweights,
filename="TEST.csv")
I get an error: Error in eval(expr, envir, enclos) : object
'WeightsVector' not found
Notice, that the function correctly prints
length(WeightsVector).
But
it looks like "lm" is looking for weights (in the 4th line of the
function) OUTSIDE the function and does not see WeightsVector.
Have you tried putting WeightsVector in the "x" dataframe? That
would seem
to reduce the potential for environmental conflation.
From the details section of help(lm):
"All of weights, subset and offset are evaluated in the same way as
variables in formula, that is first in data and then in the
environment of
formula."
Why is it looking outside the function for the object
that has just
been defined inside the function?
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