CODEWITHSUNDEEP
rlistnestednested-lists
Rappster
Rappster

Reputation: 13100

Check if a list is nested or not

Is there a "built-in"/efficient and robust way to check if list objects are nested or not?

To clarify my understanding of the term nested:

Flat or not-nested list

x.1 <- list(
    a=TRUE, 
    b=1:5
)

Nested list

x.2 <- list(
    a=list(a.1=list(a.1.1=TRUE)), 
    b=list(b.1=1:5)
)

My first idea was to use a combination of str, capture.output and regular expressions. But as everything related to regular expression: pretty powerful, pretty risky on the robustness side ;-) So I wondered if there's something better out there:

isNested <- function(x) {
    if (class(x) != "list") {
        stop("Expecting 'x' to be a list")
    }
    out <- FALSE
    strout <- capture.output(str(x))
    idx <- grep("\\$.*List", strout)
    if (length(idx)) {
        out <- TRUE
    }
    return(out)
}

> isNested(x=x.1)
[1] FALSE
> isNested(x=x.2)
[1] TRUE

Second approach courtesy of Roman and Arun:

isNested2 <- function(x) {
    if (class(x) != "list") {
        stop("Expecting 'x' to be a list")
    }
    out <- any(sapply(x, is.list))
    return(out)
}

> isNested2(x=x.1)
[1] FALSE
> isNested2(x=x.2)
[1] TRUE

Upvotes: 6

Views: 1862

Answers (4)

datawookie
datawookie

Reputation: 6584

What if the contents of the list are S3 objects which in turn have a nested list? I'd want these not to be treated as lists, so that a list of these objects is "not nested" (it's just a list of objects rather than a list of lists). Using class() rather than is.list() so that check if literally list rather than something else with an embedded list.

is.nested <- function(x) {
  stopifnot(is.list(x))
  any(sapply(x, function(x) any(class(x) == "list")))
}

Upvotes: 0

Sven Hohenstein
Sven Hohenstein

Reputation: 81743

You can use the is.list function:

any(sapply(x.1, is.list))
[1] FALSE

any(sapply(x.2, is.list))
[1] TRUE

As a function isNested:

isNested <- function(l) {
  stopifnot(is.list(l))
  for (i in l) {
    if (is.list(i)) return(TRUE)
  }
  return(FALSE)
}

Instead of testing all list elements, the function stops as soon as it detects a nested list.

Upvotes: 12

Ciar&#225;n Tobin
Ciar&#225;n Tobin

Reputation: 7536

Here's another way for the fun of it:

length(unlist(l, FALSE)) != length(unlist(l))

Or a variation on that:

!identical(unlist(l, FALSE), unlist(l))

Makes use of the recursive parameter of unlist(). With the error checking as well if you want:

isNested <- function(l) {
  if (!is.list(l)) stop("Not a list.")
  !identical(unlist(l, FALSE), unlist(l))  
}

Upvotes: 3

Pop
Pop

Reputation: 12411

Try this :

   isNested <- function(x) {
    if (is.list(x))
        stop("Expecting 'x' to be a list")

    any(unlist( lapply(x,is.list) ))
   }

Upvotes: 4

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