[R] boot with strata: strata argument ignored?

[Bryan Hanson]

Hello All.  I must be missing the really obvious here:

mm <- function(d, i) median(d[i])
b1 <- boot(gravity$g, mm, R = 1000)
b1
b2 <- boot(gravity$g, mm, R = 1000, strata = gravity$series)
b2

Both b1 and b2 seem to have done (almost) the same thing, but it looks like
the strata argument in b2 has been ignored.  However, str(b1) vs str(b2)
does show that the strata have been noted correctly.  But b2$t is a 1000 x 1
array, not a 1000 x 8 array (gravity$series is a factor with 8 levels).

There is a more complex example in ?boot using the same data set that gives
a result that seems to make sense (2 levels in the factor, so $t has 2
columns).

I either misunderstand the expected behavior or I've missed some punctuation
or syntax detail.

TIA, Bryan

*************
Bryan Hanson
Acting Chair
Professor of Chemistry & Biochemistry
DePauw University, Greencastle IN USA

> sessionInfo()
R version 2.11.0 (2010-04-22)
x86_64-apple-darwin9.8.0

locale:
[1] en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8

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

other attached packages:
 [1] boot_1.2-42        brew_1.0-3         faraway_1.0.4
 [4] GGally_0.2         xtable_1.5-6       mvbutils_2.5.1
 [7] ggplot2_0.8.7      digest_0.4.2       reshape_0.8.3
[10] proto_0.3-8        ChemoSpec_1.43     R.utils_1.4.0
[13] R.oo_1.7.2         R.methodsS3_1.2.0  rgl_0.91
[16] lattice_0.18-5     mvoutlier_1.4      plyr_0.1.9
[19] RColorBrewer_1.0-2 chemometrics_0.8   som_0.3-5
[22] robustbase_0.5-0-1 rpart_3.1-46       pls_2.1-0
[25] pcaPP_1.8-1        mvtnorm_0.9-9      nnet_7.3-1
[28] mclust_3.4.4       MASS_7.3-5         lars_0.9-7
[31] e1071_1.5-23       class_7.3-2