Bootstrapping issues

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Clive Nicholas
Sent: Monday, November 12, 2012 8:06 AM
To: r-help at r-project.org
Subject: [R] Bootstrapping issues

sessionInfo()R version 2.15.2 (2012-10-26)
Platform: i686-pc-linux-gnu (32-bit)

locale:
 [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C
LC_TIME=en_GB.UTF-8
 [4] LC_COLLATE=en_GB.UTF-8     LC_MONETARY=en_GB.UTF-8
LC_MESSAGES=en_GB.UTF-8
 [7] LC_PAPER=C                 LC_NAME=C
LC_ADDRESS=C
[10] LC_TELEPHONE=C             LC_MEASUREMENT=en_GB.UTF-8
LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] boot_1.3-7

loaded via a namespace (and not attached):
[1] tools_2.15.2


Hello. I have a very straightforward question. Here's some simulated
data
(N=500)

test<-data.frame(A=rnorm(500,mean=2.72,sd=5.36),
B=sample(c(12,20,24,28,32),size=500,prob=c(0.333,0.026,0.026,0.436,0.17
9),replace=TRUE),C=sample(c(0,1),size=500,replace=TRUE),D=sample(c(0,1)
,size=500,replace=TRUE))


head(test)          A    B    C    D
1  1.181804   28    1    0
2 -5.602307   12    1    1
3  2.925090   24    1    1
4  3.437408   28    1    0
5 -6.503531   32    0    0
6 11.013888   12    1    1


which I then bootstrap using

library(boot)

bs <- function(formula, data, indices) {   test <- data[indices,]
fit <- lm(formula, data=test)   return(coef(fit))

}


The following works

results <- boot(data=test, statistic=bs, R=1000, A~B+C+D+C*D)

results <- boot(data=test, statistic=bs, R=1000, A~B+C+D+C*D)

results


But when I then amend the dataset by changing the D variable to
simulate fixed proportions

D=sample(c(0,1),size=500,prob=c(0.564,0.436),replace=TRUE


head(test)            A  B C D
1  5.73771963 28 0 1
2 -0.19040750 12 1 0
3  2.22515982 12 0 1
4 -0.02905223 32 1 0
5  4.68314112 28 0 1
6  5.10711732 12 1 0


the same bootstrapping routine chokes with an error

results <- boot(data=test, statistic=bs, R=1000, A~B+C+C*D)Error in
data[indices, ] : incorrect number of dimensions


despite the fact that the B variable also has simulated fixed
proportions and yet the original code ran without any errors. I have
two general observations to make about this:

(1) this does not make sense; and
(2) I don't understand this.

How best to make these two observations go away and run the code to my
satisfaction?

Many thanks.

--
Clive Nicholas (clivenicholas.posterous.com)

[Please DO NOT mail me personally here, but at
<clivenicholas at hotmail.com>.
Please respond to contributions I make in a list thread here. Thanks!]

"My colleagues in the social sciences talk a great deal about
methodology.
I prefer to call it style." -- Freeman J. Dyson

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