R Under development (unstable) (2023-11-16 r85542 ucrt) -- "Unsuffered Consequences"
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> library("R.utils")
Loading required package: R.oo
Loading required package: R.methodsS3
R.methodsS3 v1.8.2 (2022-06-13 22:00:14 UTC) successfully loaded. See ?R.methodsS3 for help.
R.oo v1.25.0 (2022-06-12 02:20:02 UTC) successfully loaded. See ?R.oo for help.

Attaching package: 'R.oo'

The following object is masked from 'package:R.methodsS3':

    throw

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

    getClasses, getMethods

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

    attach, detach, load, save

R.utils v2.12.3 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, isOpen, nullfile, parse, warnings

> 
> # A data frame
> set.seed(42)
> n <- 5L
> data <- data.frame(
+   index = 1:n,
+   symbol = letters[1:n],
+   x = runif(n),
+   y = rnorm(n),
+   stringsAsFactors=FALSE
+ )
> 
> # Write to tab-delimited file (using a connection)
> pathname <- tempfile(fileext=".tsv")
> con <- file(pathname, open="w")
> writeDataFrame(data, file=con, createdBy="R.utils")
> close(con)
> 
> # Append another set of rows
> writeDataFrame(data, file=pathname, append=TRUE)
> 
> # There should only be one header and one set of column names
> print(readLines(pathname))
 [1] "# createdBy: R.utils"                                 
 [2] "# createdOn: 2023-11-17 08:50:13 CET"                 
 [3] "# nbrOfRows: 5"                                       
 [4] "# nbrOfColumns: 4"                                    
 [5] "# columnNames: index\tsymbol\tx\ty"                   
 [6] "# columnClasses: integer\tcharacter\tnumeric\tnumeric"
 [7] "index\tsymbol\tx\ty"                                  
 [8] "1\ta\t0.914806043496355\t0.0478847360942517"          
 [9] "2\tb\t0.937075413297862\t-1.10459944068306"           
[10] "3\tc\t0.286139534786344\t0.539023801893912"           
[11] "4\td\t0.830447626067325\t0.580206320853481"           
[12] "5\te\t0.641745518893003\t-0.657502835154674"          
[13] "1\ta\t0.914806043496355\t0.0478847360942517"          
[14] "2\tb\t0.937075413297862\t-1.10459944068306"           
[15] "3\tc\t0.286139534786344\t0.539023801893912"           
[16] "4\td\t0.830447626067325\t0.580206320853481"           
[17] "5\te\t0.641745518893003\t-0.657502835154674"          
> 
> # Overwrite using a connection
> con <- file(pathname, open="w")
> writeDataFrame(data, file=con, overwrite=TRUE)
> close(con)
> 
> # Overwrite using a filename
> writeDataFrame(data, file=pathname, overwrite=TRUE)
> 
> 
> proc.time()
   user  system elapsed 
   3.01   21.34   25.46