R help - Nov 2020 - paste() turns list element character vector into deparsed expression. Why?

I was just surprised by very un-intuitive behaviour of paste(), which appears to
collapse a one-column data frame or one-element list into a deparsed expression,
rather than producing the expected string. Can someone kindly explain what's
going on here?


reprex:
======
list(s = c("xyz", "uvw"))
#     s
# 1 xyz
# 2 uvw

paste(list(s = c("xyz", "uvw")), collapse = "")
# [1] "c(\"xyz\", \"uvw\")"   # This is
unexpected!

I would have expected:
# [1] "xyzuvw"
 
... which I do get with e.g.
paste(list(s = c("xyz", "uvw"))$s, collapse = "")

But what logic is there in returning a deparsed expression?



Thanks!
Boris

I think `paste()` just calls `as.character()` on each input argument
and then collapses things afterwards. Calling `as.character()` on the
first input argument generates exactly the output you show (and didn't
expect) and there is nothing to collapse. So changing `collapse = ""`
to anything else doesn't change behaviour.

The question is reduced to how `as.character()` should handle a list as
input. It seems to me that this input is so generic that it is hard to
handle graciously without all kinds of special cases. So you expect the
length one list

as.character(list(s = c("xyz", "uvw"))

to return the length 2 character vector `c("xyz", "uvw")`?
What should

as.character(list(s = c("xyz", "uvw"), t = c("a",
"b", "c"))

return?

Kind regards,
Ege

On Mon, 2020-11-09 at 11:38 +0000, Boris Steipe wrote:
> I was just surprised by very un-intuitive behaviour of paste(), which
> appears to collapse a one-column data frame or one-element list into
> a deparsed expression, rather than producing the expected string. Can
> someone kindly explain what's going on here?
> 
> 
> reprex:
> ======> 
> list(s = c("xyz", "uvw"))
> #     s
> # 1 xyz
> # 2 uvw
> 
> paste(list(s = c("xyz", "uvw")), collapse =
"")
> # [1] "c(\"xyz\", \"uvw\")"   # This is
unexpected!
> 
> I would have expected:
> # [1] "xyzuvw"
>  
> ... which I do get with e.g.
> paste(list(s = c("xyz", "uvw"))$s, collapse =
"")
> 
> But what logic is there in returning a deparsed expression?
> 
> 
> 
> Thanks!
> Boris
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Thanks Ege -

That narrows it down, ... but it's still weird.

My issue is that I don't consider "c(\"xyz\",
\"uvw\")" to be a valid character representation of a list. c()
is a function, so "c(\"xyz\", \"uvw\")" is a
string representation of a function call that could be  eval(parse(...))'ed
into a two-element vector ... but considering this a coercion seems really
weird.

What do I think your example should return? An object of the same general
structure as the input, with non-character components coerced to character. And
if that's not possible because there is no good character representation
(e.g. if its a closure) than it should return an error.


Cheers,
Boris

 

> On 2020-11-09, at 22:24, Ege Rubak <rubak at math.aau.dk> wrote:
> 
> EXTERNAL EMAIL:  Treat content with extra caution.
> 
> I think `paste()` just calls `as.character()` on each input argument
> and then collapses things afterwards. Calling `as.character()` on the
> first input argument generates exactly the output you show (and didn't
> expect) and there is nothing to collapse. So changing `collapse =
""`
> to anything else doesn't change behaviour.
> 
> The question is reduced to how `as.character()` should handle a list as
> input. It seems to me that this input is so generic that it is hard to
> handle graciously without all kinds of special cases. So you expect the
> length one list
> 
> as.character(list(s = c("xyz", "uvw"))
> 
> to return the length 2 character vector `c("xyz",
"uvw")`? What should
> 
> as.character(list(s = c("xyz", "uvw"), t =
c("a", "b", "c"))
> 
> return?
> 
> Kind regards,
> Ege
> 
> On Mon, 2020-11-09 at 11:38 +0000, Boris Steipe wrote:
>> I was just surprised by very un-intuitive behaviour of paste(), which
>> appears to collapse a one-column data frame or one-element list into
>> a deparsed expression, rather than producing the expected string. Can
>> someone kindly explain what's going on here?
>> 
>> 
>> reprex:
>> ======>> 
>> list(s = c("xyz", "uvw"))
>> #     s
>> # 1 xyz
>> # 2 uvw
>> 
>> paste(list(s = c("xyz", "uvw")), collapse =
"")
>> # [1] "c(\"xyz\", \"uvw\")"   # This is
unexpected!
>> 
>> I would have expected:
>> # [1] "xyzuvw"
>> 
>> ... which I do get with e.g.
>> paste(list(s = c("xyz", "uvw"))$s, collapse =
"")
>> 
>> But what logic is there in returning a deparsed expression?
>> 
>> 
>> 
>> Thanks!
>> Boris
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.