R devel - Mar 2023 - Multiple Assignment built into the R Interpreter?

Dear R Core,

working on my dynamic factor modelling package, which requires several
subroutines to create and update several system matrices, I come back to
the issue of being annoyed by R not supporting multiple assignment out of
the box like Matlab, Python and julia. e.g. something like

A, C, Q, R = init_matrices(X, Y, Z)

would be a great addition to the language. I know there are several
workarounds such as the %<-% operator in the zeallot package or my own %=%
operator in collapse, but these don't work well for package development as
R CMD Check warns about missing global bindings for the created variables,
e.g. I would have to use

A <- C <- Q <- R <- NULL
.c(A, C, Q, R) %=% init_matrices(X, Y, Z)

in a package, which is simply annoying. Of course the standard way of

init <- init_matrices(X, Y, Z)
 A <- init$A; C <- init$C; Q <- init$Q; R <- init$R
rm(init)

is also super cumbersome compared to Python or Julia. Another reason is of
course performance, even my %=% operator written in C has a non-negligible
performance cost for very tight loops, compared to a solution at the
interpretor level or in a primitive function such as `=`.

So my conclusion at this point is that it is just significantly easier to
implement such codes in Julia, in addition to the greater performance it
offers. There are obvious reasons why I am still coding in R and C, thanks
to the robust API and great ecosystem of packages, but adding this could be
a presumably low-hanging fruit to make my life a bit easier. Several issues
for this have been filed on Stackoverflow, the most popular one (
https://stackoverflow.com/questions/7519790/assign-multiple-new-variables-on-lhs-in-a-single-line)
has been viewed 77 thousand times.

But maybe this has already been discussed here and already decided against.
In that case, a way to browse R-devel archives to find out would be nice.

Best regards,

Sebastian

	[[alternative HTML version deleted]]

I think the standard way to do this in R is given by list2env(), as 
described in a couple of answers on the SO page you linked.

The syntax you proposed would be likely to be confusing in complex 
expressions, e.g.

   f(A, C, Q, R = init_matrices(X, Y, Z))

would obviously not work but wouldn't trigger a syntax error, and

   f((A, C, Q, R = init_matrices(X, Y, Z)))

could work, but looks too much like the previous one.  So I think R 
would want Javascript-like

   [A, C, Q, R] <- init_matrices(X, Y, Z)

instead.  But then the question would come up about how to handle the 
RHS.  Does the function have to return a list?  What if the length of 
the list is not 4?  Or is it just guaranteed to be equivalent to

   temp <- init_matrices(X, Y, Z)
   A <- temp[[1]]
   C <- temp[[2]]
   Q <- temp[[3]]
   R <- temp[[4]]

which would work for other vector types besides lists?

BTW, here's a little hack that almost works:

`vals<-` <- function(x, ..., value) {
    others <- substitute(list(...))
    if (length(others) > 1)
      for (i in seq_along(others)[-1])
        assign(as.character(others[[i]]), value[[i]], envir = 
parent.frame())
    value[[1]]
}

You call it as

  vals(a, b, c) <- 1:3

and it assigns 1 to a, 2 to b, and 3 to c.  It doesn't quite do what you 
want because it requires that a exists already, but b and c don't have to.

Duncan Murdoch

On 11/03/2023 4:04 a.m., Sebastian Martin Krantz wrote:
> Dear R Core,
> 
> working on my dynamic factor modelling package, which requires several
> subroutines to create and update several system matrices, I come back to
> the issue of being annoyed by R not supporting multiple assignment out of
> the box like Matlab, Python and julia. e.g. something like
> 
> A, C, Q, R = init_matrices(X, Y, Z)
> 
> would be a great addition to the language. I know there are several
> workarounds such as the %<-% operator in the zeallot package or my own
%=%
> operator in collapse, but these don't work well for package development
as
> R CMD Check warns about missing global bindings for the created variables,
> e.g. I would have to use
> 
> A <- C <- Q <- R <- NULL
> .c(A, C, Q, R) %=% init_matrices(X, Y, Z)
> 
> in a package, which is simply annoying. Of course the standard way of
> 
> init <- init_matrices(X, Y, Z)
>   A <- init$A; C <- init$C; Q <- init$Q; R <- init$R
> rm(init)
> 
> is also super cumbersome compared to Python or Julia. Another reason is of
> course performance, even my %=% operator written in C has a non-negligible
> performance cost for very tight loops, compared to a solution at the
> interpretor level or in a primitive function such as `=`.
> 
> So my conclusion at this point is that it is just significantly easier to
> implement such codes in Julia, in addition to the greater performance it
> offers. There are obvious reasons why I am still coding in R and C, thanks
> to the robust API and great ecosystem of packages, but adding this could be
> a presumably low-hanging fruit to make my life a bit easier. Several issues
> for this have been filed on Stackoverflow, the most popular one (
>
https://stackoverflow.com/questions/7519790/assign-multiple-new-variables-on-lhs-in-a-single-line)
> has been viewed 77 thousand times.
> 
> But maybe this has already been discussed here and already decided against.
> In that case, a way to browse R-devel archives to find out would be nice.
> 
> Best regards,
> 
> Sebastian
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

The gsubfn package can do that.

    library(gsubfn)

    # swap a and b without explicitly creating a temporary
     a <- 1; b <- 2
     list[a,b] <- list(b,a)

     # get eigenvectors and eigenvalues
     list[eval, evec] <- eigen(cbind(1,1:3,3:1))

     # get today's month, day, year
     require(chron)
     list[Month, Day, Year] <- month.day.year(unclass(Sys.Date()))

     # get first two components of linear model ignoring rest
     list[Coef, Resid] <- lm(rnorm(10) ~ seq(10))

     # assign Green and Blue (but not Red) components
     list[,Green,Blue]  <- col2rgb("aquamarine")

     # Assign QR and QRaux but not other components
     list[QR,,QRaux]  <- qr(c(1,1:3,3:1))


On Sat, Mar 11, 2023 at 7:47?AM Sebastian Martin Krantz
<sebastian.krantz at graduateinstitute.ch> wrote:
>
> Dear R Core,
>
> working on my dynamic factor modelling package, which requires several
> subroutines to create and update several system matrices, I come back to
> the issue of being annoyed by R not supporting multiple assignment out of
> the box like Matlab, Python and julia. e.g. something like
>
> A, C, Q, R = init_matrices(X, Y, Z)
>
> would be a great addition to the language. I know there are several
> workarounds such as the %<-% operator in the zeallot package or my own
%=%
> operator in collapse, but these don't work well for package development
as
> R CMD Check warns about missing global bindings for the created variables,
> e.g. I would have to use
>
> A <- C <- Q <- R <- NULL
> .c(A, C, Q, R) %=% init_matrices(X, Y, Z)
>
> in a package, which is simply annoying. Of course the standard way of
>
> init <- init_matrices(X, Y, Z)
>  A <- init$A; C <- init$C; Q <- init$Q; R <- init$R
> rm(init)
>
> is also super cumbersome compared to Python or Julia. Another reason is of
> course performance, even my %=% operator written in C has a non-negligible
> performance cost for very tight loops, compared to a solution at the
> interpretor level or in a primitive function such as `=`.
>
> So my conclusion at this point is that it is just significantly easier to
> implement such codes in Julia, in addition to the greater performance it
> offers. There are obvious reasons why I am still coding in R and C, thanks
> to the robust API and great ecosystem of packages, but adding this could be
> a presumably low-hanging fruit to make my life a bit easier. Several issues
> for this have been filed on Stackoverflow, the most popular one (
>
https://stackoverflow.com/questions/7519790/assign-multiple-new-variables-on-lhs-in-a-single-line)
> has been viewed 77 thousand times.
>
> But maybe this has already been discussed here and already decided against.
> In that case, a way to browse R-devel archives to find out would be nice.
>
> Best regards,
>
> Sebastian
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel


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

>>>>> Sebastian Martin Krantz 
>>>>>     on Sat, 11 Mar 2023 11:04:54 +0200 writes:
[............]

    > But maybe this has already been discussed here and already
    > decided against.  In that case, a way to browse R-devel
    > archives to find out would be nice.

    > Best regards,
    > Sebastian

    ....

    > ______________________________________________
    > R-devel at r-project.org mailing list
    > https://stat.ethz.ch/mailman/listinfo/r-devel

As every mailing list message contains a footer like this,
and if you know about 'site:' in Google or say, https://duckduckgo.com/
you can use search terms such as

     site:stat.ethz.ch '[R-devel]' "Multiple Assignment"
or   site:stat.ethz.ch/pipermail '[R-devel]' "Multiple
Assignment"
or   site:stat.ethz.ch/pipermail/r-devel  'Multiple Assignment'

giving results (but for me, currently,
much much better ones  on duckduckgo.com than Google.com).
"Search" from the sidebar of www.r-project.org
is https://www.r-project.org/search.html

which mentions 
- https://search.r-project.org/  
- Rseek

where Rseek is very widely searching, and (the R foundation's)
 search.r-project.org  is mainly searching on CRAN

and both give interesting hits on  'multiple assignment'

Martin