sourceTo

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Parses and evaluates code from a file or a connection

Parses and evaluates code from a file or a connection. This has the same effect as if source(..., local=TRUE) would have been called from within the given environment. This is useful when setting up a new local working environment.

Keywords
programming, IO
Usage
## S3 method for class 'default':
sourceTo(file, chdir=FALSE, ..., local=TRUE, envir=parent.frame(), modifiedOnly=FALSE)
Arguments
file
A connection or a character string giving the pathname of the file or URL to read from.
chdir
If TRUE and file is a pathname, the Rworking directory is temporarily changed to the directory containing file for evaluating.
...
Arguments to source(). If argument file is not explicitly given, the first argument is assumed to be the file argument. This argument is converted into a string by
local
If FALSE, evaluation is done in the global environment, otherwise in the calling environment.
envir
An environment in which source() should be called. If NULL, the global environment is use
modifiedOnly
If TRUE, the file is sourced only if modified since the last time it was sourced, otherwise regardless.
Value

  • Return the result of source().

Hooks

This methods recognizes the hook sourceTo/onPreprocess, which is called after the lines in file has been read, but before they have been parsed by the Rparser, cf. parse(). An onPreprocess hook function should take a character vector of code lines and return a character vector of code lines. This can for instance be used to pre-process R source code with special directives such as VComments. Note that only one hook function can be used for this function, otherwise an error is generated.

See Also

sourceDirectory(). sys.source() and source().

Aliases
  • sourceTo.default
  • sourceTo
Examples
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Example 1
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cat("=== Example 1 ================================================
")

foo <- function(file, ...) {
  cat("Local objects before calling sourceTo():
")
  print(ls())

  res <- sourceTo(file, ...)

  cat("Local objects after calling sourceTo():
")
  print(ls())
}

cat("Global objects before calling foo():
")
lsBefore <- NA
lsBefore <- ls()
foo(file=textConnection(c('a <- 1', 'b <- 2')))

cat("Global objects after calling foo():
")
stopifnot(length(setdiff(ls(), lsBefore)) == 0)


# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Example 2 - with VComments preprocessor
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cat("=== Example 2 ================================================
")

preprocessor <- function(lines, ...) {
  cat("-----------------------------------------
")
  cat("Source code before preprocessing:
")
  displayCode(code=lines, pager="console")
  cat("-----------------------------------------
")
  cat("Source code after preprocessing:
")
  lines <- VComments$compile(lines)
  displayCode(code=lines, pager="console")
  cat("-----------------------------------------
")
  lines
}

oldHooks <- getHook("sourceTo/onPreprocess")
setHook("sourceTo/onPreprocess", preprocessor, action="replace")
code <- c(
 'x <- 2',
 '#V1# threshold=-1',
 '#Vc# A v-comment log message',
 'print("Hello world")'
)
fh <- textConnection(code)
sourceTo(fh)
setHook("sourceTo/onPreprocess", oldHooks, action="replace")
Documentation reproduced from package R.utils, version 1.6.0, License: LGPL (>= 2.1)

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