[R] use of formula in survey analysis with replicated weights

[LE TERTRE Alain]

Hi there,
I would like to use a formula inside a call to withReplicates in a survey analysis.
If the initial call with formula expressed inside the function works as expected, defining the formula outside gives an error message.
See example below, adapted from survey:withReplicates help page.

library(survey)
library(quantreg)

data(api)
## one-stage cluster sample
dclus1<-svydesign( id=~dnum, weights=~pw, data=apiclus1, fpc=~fpc)
## convert to bootstrap
bclus1<-as.svrepdesign( dclus1, type="bootstrap", replicates=100)

## median regression
withReplicates( bclus1, quote( coef( rq( api00~api99, tau=0.5, weights=.weights))))
               theta     SE
(Intercept) 87.78505 18.850
api99        0.91589  0.028

# Defining formula outside
Myformula <- as.formula( " api00~api99")
# Rerun the same analysis
withReplicates( bclus1, quote( coef( rq( formula= Myformula, tau=0.5, weights=.weights))))
Erreur dans eval(expr, envir, enclos) : objet 'api00' introuvable

# I suspect the evaluation not done in the right environment. 
#If you specify with data option in rq, the initial dataframe, formula is then correctly evaluated but .weights are not found.

withReplicates( bclus1, quote( coef( rq( formula= Myformula, tau=0.5, weights=.weights, data=apiclus1 ))))
Erreur dans eval(expr, envir, enclos) : objet '.weights' introuvable

Any help greatly appreciated

O__ ---- Alain Le Tertre
 c/ /'_ --- Institut de Veille Sanitaire (InVS)/ Département Santé Environnement
(*) \(*) -- Responsable de l'unité Statistiques & Outils
~~~~~~~~~~ - 12 rue du val d'Osne
94415 Saint Maurice cedex FRANCE
Voice: 33 1 41 79 67 62 Fax: 33 1 41 79 67 68
email: a.letertre at invs.sante.fr