R devel - Dec 2020 - [External] Re: New pipe operator

On Sat, Dec 5, 2020 at 1:19 PM <luke-tierney at uiowa.edu>
wrote:
> Let's get some experience
Here is my last SO post using dplyr rewritten to use R 4.1 devel.  Seems
not too bad.  Was able to work around the placeholder for gsub by specifying
the arg names and used \(...)... elsewhere.  This does not address the
inconsistency discussed though.  I have indented by 2 spaced in case the
email wraps around.  The objective is to read myfile.csv including columns that
contain c(...) and integer(0), parsing and evaluating them.


  # taken from:
  #
https://stackoverflow.com/questions/65174764/reading-in-a-csv-that-contains-vectors-cx-y-in-r/65175172#65175172

  # create input file for testing
  Lines <-
"\"col1\",\"col2\",\"col3\"\n\"a\",1,integer(0)\n\"c\",c(3,4),5\n\"e\",6,7\n"
  cat(Lines, file = "myfile.csv")

  #########################################################################
  # base R 4.1 (devel)
  DF <- "myfile.csv" |>
    readLines() |>
    gsub(pattern = r'{(c\(.*?\)|integer\(0\))}', replacement =
r'{"\1"}') |>
    \(.) read.csv(text = .) |>
    \(.) replace(., 2:3, lapply(.[2:3], \(col) lapply(col, \(x)
eval(parse(text = x)))))

  #########################################################################
  # dplyr/magrittr
  library(dplyr)

  DF <- "myfile.csv" %>%
    readLines %>%
    gsub(r'{(c\(.*?\)|integer\(0\))}', r'{"\1"}', .)
%>%
    { read.csv(text = .) } %>%
    mutate(across(2:3, ~ lapply(., function(x) eval(parse(text = x)))))

Or, keeping dplyr but with R-devel pipe and function shorthand:

DF <- "myfile.csv" %>%
    readLines() |>
    \(.) gsub(r'{(c\(.*?\)|integer\(0\))}', r'{"\1"}',
.) |>
    \(.) read.csv(text = .) |>
    mutate(across(2:3, \(col) lapply(col, \(x) eval(parse(text = x)))))

Using named arguments to redirect to the implicit first does work,
also in magrittr, but for me at least it is the kind of thing I would
probably regret a month later when trying to figure out the code.

Best,

luke

On Mon, 7 Dec 2020, Gabor Grothendieck wrote:
> On Sat, Dec 5, 2020 at 1:19 PM <luke-tierney at uiowa.edu> wrote:
>> Let's get some experience
>
> Here is my last SO post using dplyr rewritten to use R 4.1 devel.  Seems
> not too bad.  Was able to work around the placeholder for gsub by
specifying
> the arg names and used \(...)... elsewhere.  This does not address the
> inconsistency discussed though.  I have indented by 2 spaced in case the
> email wraps around.  The objective is to read myfile.csv including columns
that
> contain c(...) and integer(0), parsing and evaluating them.
>
>
>  # taken from:
>  #
https://stackoverflow.com/questions/65174764/reading-in-a-csv-that-contains-vectors-cx-y-in-r/65175172#65175172
>
>  # create input file for testing
>  Lines <-
"\"col1\",\"col2\",\"col3\"\n\"a\",1,integer(0)\n\"c\",c(3,4),5\n\"e\",6,7\n"
>  cat(Lines, file = "myfile.csv")
>
>  #########################################################################
>  # base R 4.1 (devel)
>  DF <- "myfile.csv" |>
>    readLines() |>
>    gsub(pattern = r'{(c\(.*?\)|integer\(0\))}', replacement =
r'{"\1"}') |>
>    \(.) read.csv(text = .) |>
>    \(.) replace(., 2:3, lapply(.[2:3], \(col) lapply(col, \(x)
> eval(parse(text = x)))))
>
>  #########################################################################
>  # dplyr/magrittr
>  library(dplyr)
>
>  DF <- "myfile.csv" %>%
>    readLines %>%
>    gsub(r'{(c\(.*?\)|integer\(0\))}', r'{"\1"}',
.) %>%
>    { read.csv(text = .) } %>%
>    mutate(across(2:3, ~ lapply(., function(x) eval(parse(text = x)))))
>
-- 
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

On Mon, Dec 7, 2020 at 9:09 AM Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
>
> On Sat, Dec 5, 2020 at 1:19 PM <luke-tierney at uiowa.edu> wrote:
> > Let's get some experience
>
> Here is my last SO post using dplyr rewritten to use R 4.1 devel.  Seems
It occurred to me it would also be interesting to show this example
rewritten using John Mount's bizarro pipe
(which is clever use of syntax to get the effect of a pipe) with the
new \(x) ...
This can be done entirely in base R 4.1.  It does not use \>, just \(x)...

  "myfile.csv" ->.;
    readLines(.) ->.;
    gsub(r'{(c\(.*?\)|integer\(0\))}', r'{"\1"}', .)
->.;
    read.csv(text = .) ->.;
    replace(., 2:3, lapply(.[2:3], \(col) lapply(col, \(x)
eval(parse(text = x))))) ->.;
    . -> DF