A R list to a Haskell list, with the `clipr` package

In the previous post, I have shown how to convert a R matrix to a Haskell list. Now I will show how to convert a R list to a Haskell list.

Let’s take this list for illustration:

L <- list(c(1,2,3), c(1,2,3,4), c(1,2))
L
## [[1]]
## [1] 1 2 3
## 
## [[2]]
## [1] 1 2 3 4
## 
## [[3]]
## [1] 1 2

So, for Haskell, you want:

[ [1, 2, 3]
 ,[1, 2, 3, 4]
 ,[1, 2] 
]

Again, the clipr package is your friend. First, write the matrix in the clipboard, like this:

library(clipr)
write_clip(L, breaks="],\n", sep=", ")
## Warning in flat_str(content, breaks): Coercing content to character

No we will deal with gsub, sub and finally cat to write the output to a file.

myfile <- "list.txt"
cat("[",
    sub("\\)", "]\n]", gsub("\\)]", "]", gsub("c\\(", "[" ,read_clip()))), 
    sep="\n", file=myfile)

And then, here is the content of list.txt:

[
[1, 2, 3],
[1, 2, 3, 4],
[1, 2]
]

Now copy-paste to Haskell, it is ready.

Update 2018-04-18

I’ve realized there is an issue in the case when some elements of the list are vectors of length one. It is fixed in the following function:

list2list <- function(L, outfile="list.txt"){
  singletons_idxs <- which(lapply(L,length)==1)
  singletons <- L[singletons_idxs]
  L <- replace(L, singletons_idxs, sprintf("c(%s)", singletons))
  write_clip(L, breaks="],\n", sep=", ")
  cat("[",
      sub("\\)", "]\n]", gsub("\\)]", "]", gsub("c\\(", "[" ,read_clip()))), 
      sep="\n", file=outfile)
}

Let’s test it.

L <- list(c(1,2,3), 0, c(1,2,3,4), c(1,2))
list2list(L)
## Warning in flat_str(content, breaks): Coercing content to character

Here is the content of list.txt:

[
[1, 2, 3],
[0],
[1, 2, 3, 4],
[1, 2]
]

Fine.