data {utils} | R Documentation

## Data Sets

### Description

Loads specified data sets, or list the available data sets.

### Usage

    data(..., list = character(), package = NULL, lib.loc = NULL,
         verbose = getOption("verbose"), envir = .GlobalEnv)

### Arguments

`...` | literal character strings or names.
`list` | a character vector.
`package` | a character vector giving the package(s) to look in for data sets, or `NULL`. By default, all packages in the search path are used, then the ‘data’ subdirectory (if present) of the current working directory.
`lib.loc` | a character vector of directory names of R libraries, or `NULL`. The default value of `NULL` corresponds to all libraries currently known.
`verbose` | a logical. If `TRUE`, additional diagnostics are printed.
`envir` | the environment where the data should be loaded.

### Details

Currently, four formats of data files are supported:

1. files ending ‘.R’ or ‘.r’ are `source()`d in, with the R working directory changed temporarily to the directory containing the respective file. (`data` ensures that the utils package is attached, in case it had been run via `utils::data`.)

2. files ending ‘.RData’ or ‘.rda’ are `load()`ed.

3. files ending ‘.tab’, ‘.txt’ or ‘.TXT’ are read using `read.table(..., header = TRUE, as.is=FALSE)`, and hence result in a data frame.

4. files ending ‘.csv’ or ‘.CSV’ are read using `read.table(..., header = TRUE, sep = ";", as.is=FALSE)`, and also result in a data frame.

If more than one matching file name is found, the first on this list is used. (Files with extensions ‘.txt’, ‘.tab’ or ‘.csv’ can be compressed, with or without further extension ‘.gz’, ‘.bz2’ or ‘.xz’.)

The data sets to be loaded can be specified as a set of character strings or names, or as the character vector `list`, or as both.

For each given data set, the first two types (‘.R’ or ‘.r’, and ‘.RData’ or ‘.rda’ files) can create several variables in the load environment, which might all be named differently from the data set. The third and fourth types will always result in the creation of a single variable with the same name (without extension) as the data set.

If no data sets are specified, `data` lists the available data sets. It looks for a new-style data index in the ‘Meta’ or, if this is not found, an old-style ‘00Index’ file in the ‘data’ directory of each specified package, and uses these files to prepare a listing. If there is a ‘data’ area but no index, available data files for loading are computed and included in the listing, and a warning is given: such packages are incomplete. The information about available data sets is returned in an object of class `"packageIQR"`. The structure of this class is experimental. Where the datasets have a different name from the argument that should be used to retrieve them the index will have an entry like `beaver1 (beavers)` which tells us that dataset `beaver1` can be retrieved by the call `data(beaver)`.

If `lib.loc` and `package` are both `NULL` (the default), the data sets are searched for in all the currently loaded packages then in the ‘data’ directory (if any) of the current working directory.

If `lib.loc = NULL` but `package` is specified as a character vector, the specified package(s) are searched for first amongst loaded packages and then in the default library/ies (see `.libPaths`).

If `lib.loc` is specified (and not `NULL`), packages are searched for in the specified library/ies, even if they are already loaded from another library.

To just look in the ‘data’ directory of the current working directory, set `package = character(0)` (and `lib.loc = NULL`, the default).

### Value

A character vector of all data sets specified, or information about all available data sets in an object of class `"packageIQR"` if none were specified.

### Good practice

`data()` was originally intended to allow users to load datasets from packages for use in their examples, and as such it loaded the datasets into the workspace `.GlobalEnv`. This avoided having large datasets in memory when not in use. That need has been almost entirely superseded by lazy-loading of datasets.

The ability to specify a dataset by name (without quotes) is a convenience: in programming the datasets should be specified by character strings (with quotes).

Use of `data` within a function without an `envir` argument has the almost always undesirable side-effect of putting an object in the user's workspace (and indeed, of replacing any object of that name already there). It would almost always be better to put the object in the current evaluation environment by `data(..., envir = environment())`. However, two alternatives are usually preferable, both described in the ‘Writing R Extensions’ manual.

- For sets of data, set up a package to use lazy-loading of data.

- For objects which are system data, for example lookup tables used in calculations within the function, use a file ‘R/sysdata.rda’ in the package sources or create the objects by R code at package installation time.

A sometimes important distinction is that the second approach places objects in the namespace but the first does not. So if it is important that the function sees `mytable` as an object from the package, it is system data and the second approach should be used. In the unusual case that a package uses a lazy-loaded dataset as a default argument to a function, that needs to be specified by `::`, e.g., `survival::survexp.us`.

### Note

One can take advantage of the search order and the fact that a ‘.R’ file will change directory. If raw data are stored in ‘mydata.txt’ then one can set up ‘mydata.R’ to read ‘mydata.txt’ and pre-process it, e.g., using `transform`. For instance one can convert numeric vectors to factors with the appropriate labels. Thus, the ‘.R’ file can effectively contain a metadata specification for the plaintext formats.

### See Also

`help` for obtaining documentation on data sets, `save` for creating the second (‘.rda’) kind of data, typically the most efficient one.

The ‘Writing R Extensions’ for considerations in preparing the ‘data’ directory of a package.

### Examples

    require(utils)
    data()                         # list all available data sets
    try(data(package = "rpart") )  # list the data sets in the rpart package
    data(USArrests, "VADeaths")    # load the data sets 'USArrests' and 'VADeaths'
    ## Not run: ## Alternatively
    ds <- c("USArrests", "VADeaths"); data(list = ds)
    ## End(Not run)
    help(USArrests)                # give information on data set 'USArrests'

[Package utils version 3.3.2 Index]