| % File src/library/stats/man/nobs.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2012 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{nobs} |
| \alias{nobs} |
| \alias{nobs.default} |
| \title{ |
| Extract the Number of Observations from a Fit. |
| } |
| \description{ |
| Extract the number of \sQuote{observations} from a model fit. This is |
| principally intended to be used in computing BIC (see \code{\link{AIC}}). |
| } |
| \usage{ |
| nobs(object, ...) |
| |
| \method{nobs}{default}(object, use.fallback = FALSE, ...) |
| } |
| \arguments{ |
| \item{object}{A fitted model object.} |
| \item{use.fallback}{logical: should fallback methods be used to try to |
| guess the value?} |
| \item{\dots}{Further arguments to be passed to methods.} |
| } |
| \details{ |
| This is a generic function, with an S4 generic in package \pkg{stats4}. |
| There are methods in this package for objects of classes |
| \code{"\link{lm}"}, \code{"\link{glm}"}, \code{"\link{nls}"} and |
| \code{"\link{logLik}"}, as well as a default method (which throws an |
| error, unless \code{use.fallback = TRUE} when it looks for |
| \code{weights} and \code{residuals} components -- use with care!). |
| |
| The main usage is in determining the appropriate penalty for BIC, but |
| \code{nobs} is also used by the stepwise fitting methods |
| \code{\link{step}}, \code{\link{add1}} and \code{\link{drop1}} as a |
| quick check that different fits have been fitted to the same set of |
| data (and not, say, that further rows have been dropped because of NAs |
| in the new predictors). |
| |
| For \code{lm}, \code{glm} and \code{nls} fits, observations with zero |
| weight are not included. |
| } |
| \value{ |
| A single number, normally an integer. Could be \code{NA}. |
| } |
| \seealso{ |
| \code{\link{AIC}}. |
| } |
| \keyword{models} |