R devel - Aug 2015 - 'vapply' not returning list element names when returned element is a length-1 list

Hi all

Sorry for the confusing title. I noticed the following inconsistency:

If i have a function that returns a named list with 2 (or more) elements,
then using 'vapply' retains the names of the elements:
> vapply(1:3, function(x) list("foo" = "bar",
"hello" = "world"),
> vector("list", 2))
      [,1]    [,2]    [,3]

foo   "bar"   "bar"   "bar"

hello "world" "world" "world"


But if the function only returns one element, then the name "foo" is
lost


> vapply(1:3, function(x) list("foo" = "bar"),
vector("list", 1))
[[1]]

[1] "bar"

> [[2]]
[1] "bar"

> [[3]]
[1] "bar"


 Note that when 'lapply' is used instead, the name IS retained
>
> > lapply(1:3, function(x) list("foo" = "bar"))
> [[1]]
> [[1]]$foo
> [1] "bar"
>
> [[2]]
> [[2]]$foo
> [1] "bar"
>
> [[3]]
> [[3]]$foo
> [1] "bar"


I'm not sure if this is intentional or a bug, but it's made my life more
difficult on several occasions and I don't see any reason it would behave
like this.

Thanks

---
http://deanattali.com

	[[alternative HTML version deleted]]

> -----Original Message-----
> From: R-devel [mailto:r-devel-bounces at r-project.org] On Behalf Of Dean
Attali
> If i have a function that returns a named list with 2 (or more) elements,
> then using 'vapply' retains the names of the elements:
> .... 
> But if the function only returns one element, then the name "foo"
is lost
vapply _always simplifies_ according to the documentation.

In the first case (function return value contains more than one element, and
each ), vapply simplifies to a matrix of two lists (!).  The names
"foo" and "hello" have been added to the dimnames so you can
tell which is which.

in the second case the function return value is a single list and not a matrix
of lists (a simple list is simpler than a matrix of lists). The name of the list
('foo') has nowhere to go; instead, you would be assigning the list to a
named variable and you don't need the name 'foo'.

Whether that is inconsistent is something of a matter of perspective.
Simplification applied as far as possible will always depend on what
simplification is possible for the particular return values, so different return
values provide different behaviour.

S Ellison 


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This email and any attachments are confidential. Any use...{{dropped:8}}

Thank you, I do see that now. I still don't completely agree with the
behaviour, I hoped there would be a way to not simplify, but thank you for
pointing me to the fact that it is documented.

---
http://deanattali.com

On 5 August 2015 at 05:08, S Ellison <S.Ellison at lgcgroup.com> wrote:
>
>
> > -----Original Message-----
> > From: R-devel [mailto:r-devel-bounces at r-project.org] On Behalf Of
Dean
> Attali
> > If i have a function that returns a named list with 2 (or more)
elements,
> > then using 'vapply' retains the names of the elements:
> > ....
> > But if the function only returns one element, then the name
"foo" is lost
>
> vapply _always simplifies_ according to the documentation.
>
> In the first case (function return value contains more than one element,
> and each ), vapply simplifies to a matrix of two lists (!).  The names
> "foo" and "hello" have been added to the dimnames so
you can tell which is
> which.
>
> in the second case the function return value is a single list and not a
> matrix of lists (a simple list is simpler than a matrix of lists). The name
> of the list ('foo') has nowhere to go; instead, you would be
assigning the
> list to a named variable and you don't need the name 'foo'.
>
> Whether that is inconsistent is something of a matter of perspective.
> Simplification applied as far as possible will always depend on what
> simplification is possible for the particular return values, so different
> return values provide different behaviour.
>
> S Ellison
>
>
> *******************************************************************
> This email and any attachments are confidential. Any u...{{dropped:12}}