requireData: Attach packages as required and expose non-LazyData data sets...
In lazyData: A LazyData Facility

Description Usage Arguments Details Value Author(s) References See Also Examples

This function provides LazyData functionality for packages which do not provide it. It acts as an enhanced substitute for the base packges require function.

1
2
3

requireData(package = stop("you must specify a package"),
            lib.loc = NULL, quietly = TRUE, character.only = FALSE,
            warn.conflicts = TRUE, reallyQuietly = TRUE, ...)

`package`	The name of the package whose attachment to the search path is required. May me a name or a literal character string.
`lib.loc`	The path to the library holding the package. As for `require`.
`quietly`	Logical: should the stanandard loading message be suppressed? Ignored if `reallyQuiet` is `TRUE`.
`character.only`	Logical: should the `package` argument be treated as a character string even if not literal?
`warn.conflicts`	Should objects masked by the attachment of the package be flagged? As for `require`. Ignored if `reallyQuiet` is `TRUE`.
`reallyQuietly`	Logical: should the `package` be loaded using `suppressPackageStartupMessages`? If `TRUE`, the default, this will make the loading as quietly as possible, but will suppress potentially useful messages, such as masking information.
`...`	Additional arguments currently ignored.

The only function this package provides, requireData, is a substitute for the base function require. If the package is not already on the search path, it attaches it. In addition, if the package a) has data sets and b) does NOT use the LazyData facility, then an additonal entry is made on the search path. This is an unlocked environment initially populated by ‘promises’ (using delayedAssign) to load a copy of the data set into memory if and when it is needed.

This is done recursively for all packages attached to the search path via dependencies.

If the package appears on the search path as package:<pkg> at positon p, then any exposed data set objects appear at postion p+1 as datasets:<pkg>. The package environment is locked, but the datasets environment is not. If a data set object is needed at any stage, it is brought silently into memory at position p+1 on the search path.

Any further call to requireData(<pkg>) will reinstate the datasets as promises, thus potentially freeing memory.

The intended effect is to make data sets more conveniently available to users, to make the use of the data function largely unnecessary, and to avoid cluttering the global environment with copies of passive data set objects.

TRUE if the package was successfully attached and FALSE otherwise.

Bill Venables

Null

require, data

requireData("mgcv") ## we assume has data sets but no LazyLoad
.Search()           ## show augmented search path

## > ls("datasets:mgcv")
##[1] "columb"       "columb.polys"