Compute the number of non-missing observations.
Provides a 'default' method to handle vectors, and a method for data frames.

## Arguments

- object
Target Object

- ...
Optional parameters (currently ignored)

## Details

Calculate the number of observations in `object`.

* For numeric vectors, this is simply the number of non-NA elements, as
computed by `sum(!is.na(object))`.

* For dataframe objects, the result is a vector containing the number of
non-NA elementes of each column.

The `nobs` and `nobs.lm` functions defined in gtools are simply aliases for
the functions in the base R `stats` package, provided for backwards
compatibility.

`baytrends` borrowed `gdata::nobs` 'as is' to avoid being archived in 2020.
https://github.com/tetratech/baytrends/issues/56

## Note

The base R package `stats` now provides a S3 dispatch function for nobs, and
methods for for objects of classes "lm", "glm", "nls" and "logLik", as well
as a default method.

Since they provided a subset of the the functionality, the base method
dispatch (nobs) function and method for "lm" objects (`nobs.lm`) are, as of
gdata version 2.10.1, simply aliases for the equivalent functions in the base
R `stats` package.

Since `gdata`'s default method (`nobs.default`) processes vectors and hands
any other data/object types to `stats:::nobs.default`.

## Author

Gregory R. Warnes greg@warnes.net

## Examples

```
x <- c(1,2,3,5,NA,6,7,1,NA )
length(x)
#> [1] 9
nobs(x)
#> [1] 7
df <- data.frame(x=rnorm(100), y=rnorm(100))
df[1,1] <- NA
df[1,2] <- NA
df[2,1] <- NA
nobs(df)
#> x y
#> 98 99
fit <- lm(y ~ x, data=df)
nobs(fit)
#> [1] 98
```