Load R data from a URL or local file

Load a pre-generated R binary data file from either a local directory or a remote URL.

loadDataFile(
  filename = NULL,
  dataUrl = NULL,
  dataDir = NULL,
  priority = c("dataDir", "dataUrl")
)

Arguments

filename

Name of the .rda file to load.

dataUrl

Remote URL directory containing data files.

dataDir

Local directory containing data files.

priority

First data source to try when both dataDir and dataUrl are supplied.

Value

Object loaded from the .rda file.

Details

This function is intended for use by package-level *_load() helper functions. It allows locally cached data files to be used when available, avoiding unnecessary internet access.

If both dataDir and dataUrl are provided, priority determines which source is tried first. If loading from the first source fails, the other source is used as a fallback.

The .rda file must contain exactly one object. A file containing several objects generates an error.

Only load data from sources you trust. Loading an .rda file restores arbitrary R objects, which can include functions and other code, so dataUrl (and dataDir) should point to locations you control.

Examples

if (FALSE) { # \dontrun{
filename <- "USCensusStates_02.rda"
dataDir <- "~/Data/Spatial"
dataUrl <- "http://data.mazamascience.com/MazamaSpatialUtils/Spatial_0.8"

# Load local file
USCensusStates <- loadDataFile(filename, dataDir = dataDir)

# Load remote file
USCensusStates <- loadDataFile(filename, dataUrl = dataUrl)

# Load local file with remote file as backup
USCensusStates <- loadDataFile(
  filename,
  dataDir = dataDir,
  dataUrl = dataUrl,
  priority = "dataDir"
)

# Load remote file with local file as backup
USCensusStates <- loadDataFile(
  filename,
  dataDir = dataDir,
  dataUrl = dataUrl,
  priority = "dataUrl"
)
} # }