Evaluate an R expression and captures the output

Description

Evaluate an R expression and captures the output.

Usage

captureOutput(expr, file=NULL, append=FALSE, collapse=NULL, envir=parent.frame())

Arguments

Details

This method immitates capture.output with the major difference that it captures strings via a raw connection rather than via internal strings. The latter becomes exponentially slow for large outputs [1,2].

Value

Returns captured output as a character vector.

Author(s)

Henrik Bengtsson

References

[1] R-devel thread 'capture.output(): Using a rawConnection() [linear] instead of textConnection() [exponential]?', 2014-02-03. https://stat.ethz.ch/pipermail/r-devel/2014-February/068349.html [2] JottR blog post 'PERFORMANCE: captureOutput() is much faster than capture.output()', 2015-05-26. http://www.jottr.org/2014/05/captureOutput.html

See Also

Internally, eval() is used to evaluate the expression. and capture.output to capture the output.

Examples

# captureOutput() is much faster than capture.output()
# for large outputs when capturing to a string.
for (n in c(10e3, 20e3, 30e3, 40e3)) {
  printf("n=%d\n", n)

  x <- rnorm(n)

  t0 <- system.time({
    bfr0 <- capture.output(print(x))
  })
  print(t0)

  t1 <- system.time({
    bfr <- captureOutput(print(x))
  })
  print(t1)
  print(t1/t0)

  bfr2n <- captureOutput(print(x), collapse="\n")
  bfr2r <- captureOutput(print(x), collapse="
")

  stopifnot(identical(bfr, bfr0))
} # for (n ...)

Results

R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.

R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.

Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.

> library(R.utils)
Loading required package: R.oo
Loading required package: R.methodsS3
R.methodsS3 v1.7.1 (2016-02-15) successfully loaded. See ?R.methodsS3 for help.
R.oo v1.20.0 (2016-02-17) successfully loaded. See ?R.oo for help.

Attaching package: 'R.oo'

The following objects are masked from 'package:methods':

    getClasses, getMethods

The following objects are masked from 'package:base':

    attach, detach, gc, load, save

R.utils v2.3.0 (2016-04-13) successfully loaded. See ?R.utils for help.

Attaching package: 'R.utils'

The following object is masked from 'package:utils':

    timestamp

The following objects are masked from 'package:base':

    cat, commandArgs, getOption, inherits, isOpen, parse, warnings

> png(filename="/home/ddbj/snapshot/RGM3/R_CC/result/R.utils/captureOutput.Rd_%03d_medium.png", width=480, height=480)
> ### Name: captureOutput
> ### Title: Evaluate an R expression and captures the output
> ### Aliases: captureOutput
> ### Keywords: IO programming
> 
> ### ** Examples
> 
> # captureOutput() is much faster than capture.output()
> # for large outputs when capturing to a string.
> for (n in c(10e3, 20e3, 30e3, 40e3)) {
+   printf("n=%d\n", n)
+ 
+   x <- rnorm(n)
+ 
+   t0 <- system.time({
+     bfr0 <- capture.output(print(x))
+   })
+   print(t0)
+ 
+   t1 <- system.time({
+     bfr <- captureOutput(print(x))
+   })
+   print(t1)
+   print(t1/t0)
+ 
+   bfr2n <- captureOutput(print(x), collapse="\n")
+   bfr2r <- captureOutput(print(x), collapse="
")
+ 
+   stopifnot(identical(bfr, bfr0))
+ } # for (n ...)
n=10000
   user  system elapsed 
  0.024   0.000   0.024 
   user  system elapsed 
  0.008   0.000   0.010 
     user    system   elapsed 
0.3333333       NaN 0.4166667 
n=20000
   user  system elapsed 
  0.068   0.004   0.072 
   user  system elapsed 
  0.020   0.000   0.018 
     user    system   elapsed 
0.2941176 0.0000000 0.2500000 
n=30000
   user  system elapsed 
  0.160   0.000   0.164 
   user  system elapsed 
  0.028   0.000   0.027 
     user    system   elapsed 
0.1750000       NaN 0.1646341 
n=40000
   user  system elapsed 
  0.280   0.000   0.281 
   user  system elapsed 
  0.036   0.000   0.035 
     user    system   elapsed 
0.1285714       NaN 0.1245552 
> 
> 
> 
> 
> 
> dev.off()
null device 
          1 
>