Re: [Rd] List comprehensions for R
That seems quite nice.
Note that there has been some related code posted. See:
http://tolstoy.newcastle.edu.au/R/help/03b/6406.html
which discusses some R idioms for list comprehensions.
Also the gsubfn package has some functionality in this direction. We
preface any function with fn$ to allow functions in its arguments
to be specified as formulas. Its more R-ish than your code and
applies to more than just list comprehensions while your code is
more faithful to list comprehensions.
> library(gsubfn)
> fn$sapply(0:11/11, ~ sin(x))
[1] 0. 0.09078392 0.18081808 0.26935891 0.35567516 0.43905397
[7] 0.51880673 0.59427479 0.66483486 0.72990422 0.78894546 0.84147098
> fn$sapply(0:4, y ~ fn$sapply(0:3, x ~ x*y))
[,1] [,2] [,3] [,4] [,5]
[1,]00000
[2,]01234
[3,]02468
[4,]0369 12
> fn$sapply(0:4, y ~ fn$sapply(0:y, x ~ x*y))
[[1]]
[1] 0
[[2]]
[1] 0 1
[[3]]
[1] 0 2 4
[[4]]
[1] 0 3 6 9
[[5]]
[1] 0 4 8 12 16
> unlist(fn$sapply(1:4, y ~ fn$sapply(1:y, x ~ x*y)))
[1] 1 2 4 3 6 9 4 8 12 16
On Dec 9, 2007 4:41 PM, David C. Norris
<[EMAIL PROTECTED]> wrote:
> Below is code that introduces a list comprehension syntax into R,
> allowing expressions like:
>
> > .[ sin(x) ~ x <- (0:11)/11 ]
> [1] 0. 0.09078392 0.18081808 0.26935891 0.35567516 0.43905397
> [7] 0.51880673 0.59427479 0.66483486 0.72990422 0.78894546 0.84147098
> > .[ .[x*y ~ x <- 0:3] ~ y <- 0:4]
> [,1] [,2] [,3] [,4] [,5]
> [1,]00000
> [2,]01234
> [3,]02468
> [4,]0369 12
> > .[ .[x+y ~ x <- 0:y] ~ y <- 0:4]
> [[1]]
> [1] 0
>
> [[2]]
> [1] 1 2
>
> [[3]]
> [1] 2 3 4
>
> [[4]]
> [1] 3 4 5 6
>
> [[5]]
> [1] 4 5 6 7 8
>
> > .[ x*y ~ {x <- 1:4; y<-1:x} ]
> [1] 1 2 4 3 6 9 4 8 12 16
>
> These constructions are supported by the following code.
>
> Regards,
> David
>
> ##
> ## Define syntax for list/vector/array comprehensions
> ##
>
> . <<- structure(NA, class="comprehension")
>
> comprehend <- function(expr, vars, seqs, comprehension=list()){
> if(length(vars)==0) # base case
>comprehension[[length(comprehension)+1]] <- eval(expr)
> else
>for(elt in eval(seqs[[1]])){
> assign(vars[1], elt, inherits=TRUE)
> comprehension <- comprehend(expr, vars[-1], seqs[-1], comprehension)
>}
> comprehension
> }
>
> ## Support general syntax like .[{exprs} ~ {generators}]
> "[.comprehension" <- function(x, f){
> f <- substitute(f)
> ## To allow omission of braces around a lone comprehension generator,
> ## as in 'expr ~ var <- seq' we make allowances for two shapes of f:
> ##
> ## (1)(`<-` (`~` expr
> ## var)
> ## seq)
> ## and
> ##
> ## (2)(`~` expr
> ## (`{` (`<-` var1 seq1)
> ## (`<-` var2 seq2)
> ## ...
> ## (`<-` varN <- seqN)))
> ##
> ## In the former case, we set gens <- list(var <- seq), unifying the
> ## treatment of both shapes under the latter, more general one.
> syntax.error <- "Comprehension expects 'expr ~ {x1 <- seq1; ... ; xN
> <- seqN}'."
> if(!is.call(f) || (f[[1]]!='<-' && f[[1]]!='~'))
>stop(syntax.error)
> if(is(f,'<-')){ # (1)
>lhs <- f[[2]]
>if(!is.call(lhs) || lhs[[1]] != '~')
> stop(syntax.error)
>expr <- lhs[[2]]
>var <- as.character(lhs[[3]])
>seq <- f[[3]]
>gens <- list(call('<-', var, seq))
> } else { # (2)
>expr <- f[[2]]
>gens <- as.list(f[[3]])[-1]
>if(any(lapply(gens, class) != '<-'))
> stop(syntax.error)
> }
> ## Fill list comprehension .LC
> vars <- as.character(lapply(gens, function(g) g[[2]]))
> seqs <- lapply(gens, function(g) g[[3]])
> .LC <- comprehend(expr, vars, seqs)
> ## Provided the result is rectangular, convert it to a vector or array
> ## TODO: Extend to handle .LC structures more than 2-deep.
> if(!length(.LC))
>return(.LC)
> dim1 <- dim(.LC[[1]])
> if(is.null(dim1)){
>lengths <- sapply(.LC, length)
>if(all(lengths == lengths[1])){ # rectangular
> .LC <- unlist(.LC)
> if(lengths[1] > 1) # matrix
>dim(.LC) <- c(lengths[1], length(lengths))
>} else { # ragged
> # leave .LC as a list
>}
> } else { # elements of .LC have dimension
>dim <- c(dim1, length(.LC))
>.LC <- unlist(.LC)
>dim(.LC) <- dim
> }
> .LC
> }
>
> __
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
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[Rd] List comprehensions for R
Below is code that introduces a list comprehension syntax into R,
allowing expressions like:
> .[ sin(x) ~ x <- (0:11)/11 ]
[1] 0. 0.09078392 0.18081808 0.26935891 0.35567516 0.43905397
[7] 0.51880673 0.59427479 0.66483486 0.72990422 0.78894546 0.84147098
> .[ .[x*y ~ x <- 0:3] ~ y <- 0:4]
[,1] [,2] [,3] [,4] [,5]
[1,]00000
[2,]01234
[3,]02468
[4,]0369 12
> .[ .[x+y ~ x <- 0:y] ~ y <- 0:4]
[[1]]
[1] 0
[[2]]
[1] 1 2
[[3]]
[1] 2 3 4
[[4]]
[1] 3 4 5 6
[[5]]
[1] 4 5 6 7 8
> .[ x*y ~ {x <- 1:4; y<-1:x} ]
[1] 1 2 4 3 6 9 4 8 12 16
These constructions are supported by the following code.
Regards,
David
##
## Define syntax for list/vector/array comprehensions
##
. <<- structure(NA, class="comprehension")
comprehend <- function(expr, vars, seqs, comprehension=list()){
if(length(vars)==0) # base case
comprehension[[length(comprehension)+1]] <- eval(expr)
else
for(elt in eval(seqs[[1]])){
assign(vars[1], elt, inherits=TRUE)
comprehension <- comprehend(expr, vars[-1], seqs[-1], comprehension)
}
comprehension
}
## Support general syntax like .[{exprs} ~ {generators}]
"[.comprehension" <- function(x, f){
f <- substitute(f)
## To allow omission of braces around a lone comprehension generator,
## as in 'expr ~ var <- seq' we make allowances for two shapes of f:
##
## (1)(`<-` (`~` expr
## var)
## seq)
## and
##
## (2)(`~` expr
## (`{` (`<-` var1 seq1)
## (`<-` var2 seq2)
## ...
## (`<-` varN <- seqN)))
##
## In the former case, we set gens <- list(var <- seq), unifying the
## treatment of both shapes under the latter, more general one.
syntax.error <- "Comprehension expects 'expr ~ {x1 <- seq1; ... ; xN
<- seqN}'."
if(!is.call(f) || (f[[1]]!='<-' && f[[1]]!='~'))
stop(syntax.error)
if(is(f,'<-')){ # (1)
lhs <- f[[2]]
if(!is.call(lhs) || lhs[[1]] != '~')
stop(syntax.error)
expr <- lhs[[2]]
var <- as.character(lhs[[3]])
seq <- f[[3]]
gens <- list(call('<-', var, seq))
} else { # (2)
expr <- f[[2]]
gens <- as.list(f[[3]])[-1]
if(any(lapply(gens, class) != '<-'))
stop(syntax.error)
}
## Fill list comprehension .LC
vars <- as.character(lapply(gens, function(g) g[[2]]))
seqs <- lapply(gens, function(g) g[[3]])
.LC <- comprehend(expr, vars, seqs)
## Provided the result is rectangular, convert it to a vector or array
## TODO: Extend to handle .LC structures more than 2-deep.
if(!length(.LC))
return(.LC)
dim1 <- dim(.LC[[1]])
if(is.null(dim1)){
lengths <- sapply(.LC, length)
if(all(lengths == lengths[1])){ # rectangular
.LC <- unlist(.LC)
if(lengths[1] > 1) # matrix
dim(.LC) <- c(lengths[1], length(lengths))
} else { # ragged
# leave .LC as a list
}
} else { # elements of .LC have dimension
dim <- c(dim1, length(.LC))
.LC <- unlist(.LC)
dim(.LC) <- dim
}
.LC
}
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Re: [Rd] Using Fortran 95 in an R package?
Dear Brian, Thank you for this. John > -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Prof Brian Ripley > Sent: Sunday, December 09, 2007 1:05 PM > To: John Fox > Cc: r-devel@r-project.org > Subject: Re: [Rd] Using Fortran 95 in an R package? > > On Sun, 9 Dec 2007, John Fox wrote: > > > Dear R-devel list members, > > > > What's the best current advice about writing Fortran code > for use in R > > packages? The Writing R Extensions manual still says that > the .Fortran > > interface is primarily intended for FORTRAN 77 code. In particular, > > are there portability issues if I use Fortran 95 in a package? For > > example, I see that Rtools for Windows now include the > gfortran compiler. > > Yes, there are still portability issues. We do still see > quite a few people using gcc3/g77 (especially on older Linux > and commercial Unices) and there are further issues if you > make use of subprogram names containing underlines. We don't > distribute a cross-building solution for Windows using > gfortran (although one can be built, it will not be mature > until gcc 4.3.x is out). > > However, I would not let that deter you: just use .f95 > extensions on the Fortran 95 files and avoid underlines. For > Windows users you are effectively requiring R >= 2.6.0. > > Brian > > -- > Brian D. Ripley, [EMAIL PROTECTED] > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UKFax: +44 1865 272595 > > __ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] Using Fortran 95 in an R package?
On Sun, 9 Dec 2007, John Fox wrote: > Dear R-devel list members, > > What's the best current advice about writing Fortran code for use in R > packages? The Writing R Extensions manual still says that the .Fortran > interface is primarily intended for FORTRAN 77 code. In particular, are > there portability issues if I use Fortran 95 in a package? For example, I > see that Rtools for Windows now include the gfortran compiler. Yes, there are still portability issues. We do still see quite a few people using gcc3/g77 (especially on older Linux and commercial Unices) and there are further issues if you make use of subprogram names containing underlines. We don't distribute a cross-building solution for Windows using gfortran (although one can be built, it will not be mature until gcc 4.3.x is out). However, I would not let that deter you: just use .f95 extensions on the Fortran 95 files and avoid underlines. For Windows users you are effectively requiring R >= 2.6.0. Brian -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UKFax: +44 1865 272595 __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
[Rd] Using Fortran 95 in an R package?
Dear R-devel list members, What's the best current advice about writing Fortran code for use in R packages? The Writing R Extensions manual still says that the .Fortran interface is primarily intended for FORTRAN 77 code. In particular, are there portability issues if I use Fortran 95 in a package? For example, I see that Rtools for Windows now include the gfortran compiler. (I know that this question has come up before, but not, as far as I can see, in the last year.) Thanks, John John Fox, Professor Department of Sociology McMaster University Hamilton, Ontario Canada L8S 4M4 905-525-9140x23604 http://socserv.mcmaster.ca/jfox __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
