Re: [R] update.formula() to add interaction terms
Many thanks, that is exactly what I was looking for. I did not know about
bquote, interesting!
MP
On Mon, Feb 3, 2014 at 6:29 PM, William Dunlap wdun...@tibco.com wrote:
Is this the sort of thing you are looking for?
fm - y ~ x1 + x2 + x3 + log(x4)
# Use terms() instead of just all.vars() to keep log(x4) as log(x4)
xVars - with(attributes(terms(fm)),
as.list(variables)[-c(1,response+1)])
str(xVars)
List of 4
$ : symbol x1
$ : symbol x2
$ : symbol x3
$ : language log(x4)
# use bquote to make the addition to the formula
update(fm, bquote( ~ . + .(xVars[[1]]) * .(xVars[[length(xVars)]])))
y ~ x1 + x2 + x3 + log(x4) + x1:log(x4)
As a function it would be
addInteraction - function(formula){
xVars - with(attributes(terms(formula)),
as.list(variables)[-c(1,response+1)])
update(formula, bquote( ~ . + .(xVars[[1]]) *
.(xVars[[length(xVars)]])))
}
used as
addInteraction(y~x1+x2+sqrt(x3))
y ~ x1 + x2 + sqrt(x3) + x1:sqrt(x3)
If the last 'term' in the formula is a compound like x4:x5 and you
want x1:x4:x5 added you will need to do more work (look at the
'factors' attribute of terms()'s output) - currently it adds x1:x5.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
-Original Message-
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org]
On Behalf
Of Marie-Pierre Sylvestre
Sent: Monday, February 03, 2014 12:54 PM
To: r-help@r-project.org
Subject: [R] update.formula() to add interaction terms
Hi,
I have a list of formulae that I need to modify. For each formula, I need
to add an interaction term between the first independent variable and the
last one. I want to write a function to achieve that because the list of
formulae to modify is long.
For example, if the formula is y ~ x1 + x2 + x3 + x4, then I need to turn
it either into
y ~ x1*x4 + x2 + x3
or
y ~ x1 + x2 + x3 + x4 + x4:x1
(I know they are the same, but one may be easier to work with than the
other).
Suppose I have the formula a which is defined as a - formula(y ~
x1+x2+x3+x4)
I know how to access to the first and last independent variables of my
formula:
firstvar - all.vars(a[[3]])[1]
lastvar - all.vars(a[[3]])[length( all.vars(a[[3]]))]
What I can't figure out is how to use update.formula() to include my
interaction term in order to get y ~ x1+x2+x3+x4 + x1:x4. Specifically,
update.formula(a, ~ . + paste(all.vars(a[[3]])[1],firstvar, lastvar, sep
=
':'))
is not producing y ~ x1+x2+x3+x4 + x1:x4.
Any idea?
Thanks in advance,
MP
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[R] update.formula() to add interaction terms
Hi, I have a list of formulae that I need to modify. For each formula, I need to add an interaction term between the first independent variable and the last one. I want to write a function to achieve that because the list of formulae to modify is long. For example, if the formula is y ~ x1 + x2 + x3 + x4, then I need to turn it either into y ~ x1*x4 + x2 + x3 or y ~ x1 + x2 + x3 + x4 + x4:x1 (I know they are the same, but one may be easier to work with than the other). Suppose I have the formula a which is defined as a - formula(y ~ x1+x2+x3+x4) I know how to access to the first and last independent variables of my formula: firstvar - all.vars(a[[3]])[1] lastvar - all.vars(a[[3]])[length( all.vars(a[[3]]))] What I can't figure out is how to use update.formula() to include my interaction term in order to get y ~ x1+x2+x3+x4 + x1:x4. Specifically, update.formula(a, ~ . + paste(all.vars(a[[3]])[1],firstvar, lastvar, sep = ':')) is not producing y ~ x1+x2+x3+x4 + x1:x4. Any idea? Thanks in advance, MP [[alternative HTML version deleted]] __ 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.
Re: [R] update.formula() to add interaction terms
Is this the sort of thing you are looking for?
fm - y ~ x1 + x2 + x3 + log(x4)
# Use terms() instead of just all.vars() to keep log(x4) as log(x4)
xVars - with(attributes(terms(fm)), as.list(variables)[-c(1,response+1)])
str(xVars)
List of 4
$ : symbol x1
$ : symbol x2
$ : symbol x3
$ : language log(x4)
# use bquote to make the addition to the formula
update(fm, bquote( ~ . + .(xVars[[1]]) * .(xVars[[length(xVars)]])))
y ~ x1 + x2 + x3 + log(x4) + x1:log(x4)
As a function it would be
addInteraction - function(formula){
xVars - with(attributes(terms(formula)),
as.list(variables)[-c(1,response+1)])
update(formula, bquote( ~ . + .(xVars[[1]]) * .(xVars[[length(xVars)]])))
}
used as
addInteraction(y~x1+x2+sqrt(x3))
y ~ x1 + x2 + sqrt(x3) + x1:sqrt(x3)
If the last 'term' in the formula is a compound like x4:x5 and you
want x1:x4:x5 added you will need to do more work (look at the
'factors' attribute of terms()'s output) - currently it adds x1:x5.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
-Original Message-
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf
Of Marie-Pierre Sylvestre
Sent: Monday, February 03, 2014 12:54 PM
To: r-help@r-project.org
Subject: [R] update.formula() to add interaction terms
Hi,
I have a list of formulae that I need to modify. For each formula, I need
to add an interaction term between the first independent variable and the
last one. I want to write a function to achieve that because the list of
formulae to modify is long.
For example, if the formula is y ~ x1 + x2 + x3 + x4, then I need to turn
it either into
y ~ x1*x4 + x2 + x3
or
y ~ x1 + x2 + x3 + x4 + x4:x1
(I know they are the same, but one may be easier to work with than the
other).
Suppose I have the formula a which is defined as a - formula(y ~
x1+x2+x3+x4)
I know how to access to the first and last independent variables of my
formula:
firstvar - all.vars(a[[3]])[1]
lastvar - all.vars(a[[3]])[length( all.vars(a[[3]]))]
What I can't figure out is how to use update.formula() to include my
interaction term in order to get y ~ x1+x2+x3+x4 + x1:x4. Specifically,
update.formula(a, ~ . + paste(all.vars(a[[3]])[1],firstvar, lastvar, sep =
':'))
is not producing y ~ x1+x2+x3+x4 + x1:x4.
Any idea?
Thanks in advance,
MP
[[alternative HTML version deleted]]
__
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.
__
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.
