R devel - Aug 2021 - problem with pipes, textConnection and read.dcf

This gives an error bit if the first gsub line is commented out then there is no
error even though it is equivalent code.

  L <- c("Variable:id", "Length:112630     ")

  L |>
    gsub(pattern = " ", replacement = "") |>
    gsub(pattern = " ", replacement = "") |>
    textConnection() |>
    read.dcf()
  ## Error in textConnection(gsub(gsub(L, pattern = " ", replacement =
""),  :
  ##  argument 'object' must deparse to a single character string

That is this works:

  L |>
    # gsub(pattern = " ", replacement = "") |>
    gsub(pattern = " ", replacement = "") |>
    textConnection() |>
    read.dcf()
  ##      Variable Length
  ## [1,] "id"     "112630"

  R.version.string
  ## [1] "R version 4.1.0 RC (2021-05-16 r80303)"
  win.version()
  ## [1] "Windows 10 x64 (build 19042)"

-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com

It's not a pipe issue:
> textConnection(gsub(gsub(L, pattern = " ", replacement =
""), pattern = " ", replacement = ""))
Error in textConnection(gsub(gsub(L, pattern = " ", replacement =
""),  :
  argument 'object' must deparse to a single character
string
> textConnection(gsub(L, pattern = " ", replacement =
""))
A connection with                                                          
description "gsub(L, pattern = \" \", replacement =
\"\")"
class       "textConnection"                              
mode        "r"                                           
text        "text"                                        
opened      "opened"                                      
can read    "yes"                                         
can write   "no"                                          

I suppose the culprit is that the deparse(substitute(...)) construct in the
definition of textConnection() can generate multiple lines if the object
expression gets complicated.
> textConnection
function (object, open = "r", local = FALSE, name =
deparse(substitute(object)),
    encoding = c("", "bytes", "UTF-8")) 

This also suggests that setting name=something might be a cure.

-pd

> On 10 Aug 2021, at 21:33 , Gabor Grothendieck <ggrothendieck at
gmail.com> wrote:
> 
> This gives an error bit if the first gsub line is commented out then there
is no
> error even though it is equivalent code.
> 
>  L <- c("Variable:id", "Length:112630     ")
> 
>  L |>
>    gsub(pattern = " ", replacement = "") |>
>    gsub(pattern = " ", replacement = "") |>
>    textConnection() |>
>    read.dcf()
>  ## Error in textConnection(gsub(gsub(L, pattern = " ",
replacement = ""),  :
>  ##  argument 'object' must deparse to a single character string
> 
> That is this works:
> 
>  L |>
>    # gsub(pattern = " ", replacement = "") |>
>    gsub(pattern = " ", replacement = "") |>
>    textConnection() |>
>    read.dcf()
>  ##      Variable Length
>  ## [1,] "id"     "112630"
> 
>  R.version.string
>  ## [1] "R version 4.1.0 RC (2021-05-16 r80303)"
>  win.version()
>  ## [1] "Windows 10 x64 (build 19042)"
> 
> -- 
> Statistics & Software Consulting
> GKX Group, GKX Associates Inc.
> tel: 1-877-GKX-GROUP
> email: ggrothendieck at gmail.com
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

Not an issue with pipes. The pipe just rewrites the expression to a
nested call and that is then evaluated. The call this produces is
> quote(L |>
+    gsub(pattern = " ", replacement = "") |>
+    gsub(pattern = " ", replacement = "") |>
+    textConnection() |>
+    read.dcf())
read.dcf(textConnection(gsub(gsub(L, pattern = " ", replacement =
""),
     pattern = " ", replacement = "")))

If you run that expression, or just the argument to read.dcf, then you
get the error you report. So the issue is somewhere in textConnection().
This produces a similar message:

read.dcf(textConnection(c(L, "aaaaaaaaaaaaaaaaaa",
"bbbbbbbbbbbbbbbb", "cccccccccccccccc",
"ddddddddddddddddddd")))

File a bug report and someone who understands the textConnection()
internals better than I do can take a look.

Best,

luke

On Tue, 10 Aug 2021, Gabor Grothendieck wrote:
> This gives an error bit if the first gsub line is commented out then there
is no
> error even though it is equivalent code.
>
>  L <- c("Variable:id", "Length:112630     ")
>
>  L |>
>    gsub(pattern = " ", replacement = "") |>
>    gsub(pattern = " ", replacement = "") |>
>    textConnection() |>
>    read.dcf()
>  ## Error in textConnection(gsub(gsub(L, pattern = " ",
replacement = ""),  :
>  ##  argument 'object' must deparse to a single character string
>
> That is this works:
>
>  L |>
>    # gsub(pattern = " ", replacement = "") |>
>    gsub(pattern = " ", replacement = "") |>
>    textConnection() |>
>    read.dcf()
>  ##      Variable Length
>  ## [1,] "id"     "112630"
>
>  R.version.string
>  ## [1] "R version 4.1.0 RC (2021-05-16 r80303)"
>  win.version()
>  ## [1] "Windows 10 x64 (build 19042)"
>
>
-- 
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:   luke-tierney at uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu