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\name{nobsY}
\alias{nobsY}
\title{Compute Number of Observations for Left Hand Side of Formula}
\usage{
nobsY(formula, group=NULL, data = NULL, subset = NULL,
na.action = na.retain, matrixna=c('all', 'any'))
}
\arguments{
\item{formula}{a formula object}
\item{group}{character string containing optional name of a
stratification variable for computing sample sizes}
\item{data}{a data frame}
\item{subset}{an optional subsetting criterion}
\item{na.action}{an optional \code{NA}-handling function}
\item{matrixna}{set to \code{"all"} if an observation is to be
considered \code{NA} if all the columns of the variable are
\code{NA}, otherwise use \code{matrixna="any"} to consider the row
missing if any of the columns are missing}
}
\value{an integer, with an attribute \code{"formula"} containing the
original formula but with an \code{id} variable (if present) removed}
\description{
After removing any artificial observations added by
\code{addMarginal}, computes the number of
non-missing observations for all left-hand-side variables in
\code{formula}. If \code{formula} contains a term \code{id(variable)}
\code{variable} is assumed to be a subject ID variable, and only unique
subject IDs are counted. If group is given and its value is the name of
a variable in the right-hand-side of the model, an additional object
\code{nobsg} is returned that is a matrix with as many columns as there
are left-hand variables, and as many rows as there are levels to the
\code{group} variable. This matrix has the further breakdown of unique
non-missing observations by \code{group}. The concatenation of all ID
variables, is returned in a \code{list} element \code{id}.
}
\examples{
d <- expand.grid(sex=c('female', 'male', NA),
country=c('US', 'Romania'),
reps=1:2)
d$subject.id <- c(0, 0, 3:12)
dm <- addMarginal(d, sex, country)
dim(dm)
nobsY(sex + country ~ 1, data=d)
nobsY(sex + country ~ id(subject.id), data=d)
nobsY(sex + country ~ id(subject.id) + reps, group='reps', data=d)
nobsY(sex ~ 1, data=d)
nobsY(sex ~ 1, data=dm)
nobsY(sex ~ id(subject.id), data=dm)
}
\keyword{utilities}
\keyword{manip}
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