R: Extract the Number of Observations from a Fit.

nobs {stats} | R Documentation

## Extract the Number of Observations from a Fit.

### Description

Extract the number of ‘observations’ from a model fit. This is principally intended to be used in computing BIC (see `AIC`).

### Usage

    nobs(object, ...)

    ## Default S3 method:
    nobs(object, use.fallback = FALSE, ...)

### Arguments

`object` | A fitted model object.
`use.fallback` | logical: should fallback methods be used to try to guess the value?
`...` | Further arguments to be passed to methods.

### Details

This is a generic function, with an S4 generic in package stats4. There are methods in this package for objects of classes `"lm"`, `"glm"`, `"nls"` and `"logLik"`, as well as a default method (which throws an error, unless `use.fallback = TRUE` when it looks for `weights` and `residuals` components – use with care!).

The main usage is in determining the appropriate penalty for BIC, but `nobs` is also used by the stepwise fitting methods `step`, `add1` and `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 `lm`, `glm` and `nls` fits, observations with zero weight are not included.

### Value

A single number, normally an integer. Could be `NA`.

### See Also

`AIC`.

[Package stats version 3.1.2 Index]