Dear R help listers,
I am trying to replicate results in Gelman and Hill's book (Chapter 3
in regressions and multilevel models). Below I estimated two models
(chp3.1 and chp3.3 in R codes) with the same data and dependent
variable but different independent variables. I have been using Stata
for quite a while, and I know I can use foreach to build a loop to
condense the codes (especially if I have a large number of models to
run).
In Stata, it would be something like:
****************************************************
// read in data
use kidiq, clear
// run two regression
reg kid_score mom_hs
reg kid_score mom_iq
// the next three lines are equivalent of the previous two lines
foreach var in mom_hs mom_iq {
reg kid_score `var'
}
***************************************************
So I want to figure out how to use R to do this. Below are my codes:
####################################################
library(foreign)
# read in stata data file
kidiq <-data.frame(read.dta('kidiq.dta', convert.factor=FALSE))
# bivariate regressions
chp3.1 <- lm(kid_score ~ mom_hs, data=kidiq)
summary(chp3.1)
chp3.3 <- lm(kid_score ~ mom_iq, data=kidiq)
summary(chp3.3)
clist <- c("mom_iq", "mom_hs")
for (x in clist) {
lm(kid_score ~ x, data = kidiq)
}
Error in model.frame.default(formula = kid_score ~ x, data = kidiq,
drop.unused.levels = TRUE) :
variable lengths differ (found for 'x')
##################################################
But I got an error message that says variable length differ. I tried
various ways to work around this, for example, I tried:
clist <- c("mom_iq", "mom_hs")
for (x in 1:length(clist)) {
lm(kid_score ~ clist[x], data = kidiq)
}
But none of these work. So I am wondering if anyone could give me
some hint. Thanks a lot
Jun Xu, PhD
Assistant Professor
Department of Sociology
Ball State University
Muncie, IN
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