[R] recursive lapply and keeping track of data

[William Dunlap]

You could replace your 'depth' argument with one that shows where in the
original data you are at:

leaf.func <-
function(data, where) {
        if(is.null(data)) stop("Null data at ", deparse(where))
        return(mean(data))
}
visit.level <-
function(data, where = integer()) {
        if (length(where) == 2) {
                return(leaf.func(data, where))
        } else {
                res <- lapply(seq_along(data), function(i)
visit.level(data[[i]], where = c(where, i)))
                names(res) <- names(data)
                return(res)
        }
}

E.g.,
> new.data <- visit.level(data, integer())
Error in leaf.func(data, where) : Null data at c(3L, 2L)
> data[[3]][2]
$Madrid
NULL




Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Mon, Aug 14, 2017 at 11:43 AM, Giovanni Gherdovich <
g.gherdovich at gmail.com> wrote:

> Hello,
>
> I'm writing a program that takes a tree in input (nested lists) and
> returns a copy of it replacing the leaves with something else (eg: a
> computation done on the original leaves).
> In the example below, the tree is composed by countries and cities,
> and the leaves (children of the cities) are vectors of numbers. The
> program takes this tree and replaces the vectors at the bottom by
> their mean.
>
> I use a recursive function and lapply, and I give names to the
> returned list after I get them from lapply. I was happy until I
> realised that when I have some anomaly in the data (in the example at
> Spain/Madrid I have NULL instead of a vector -- I simulate an error
> artificially with stop()) I have no way to trace where in the original
> tree is the problem, as the names are lost when I do lapply. I was
> thinking to use tryCatch() and do something smart at error/warning,
> but I'm afraid the information is all lost.
>
> Is there any obvious way I am missing that would give me the debug
> information I need? In the example above ideally I'd like to know that
> the program stopped at the path Spain/Madrid.
>
>
> # ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
> data <- list("France" = list("Paris" = c(21, 34, 42),
>                              "Marseille" = c(23, 51, 64),
>                              "Toulouse" = c(78, 43, 25)),
>              "Germany" = list("Berlin" = c(43, 20, 87),
>                               "Munich" = c(89, 45, 34),
>                               "Hamburg" = c(98, 78, 32)),
>              "Spain" = list("Barcelona" = c(43, 49, 72),
>                             "Madrid" = NULL,
>                             "Valencia" = c(23, 23, 76)))
>
> leaf.func <- function(data) {
>         if(is.null(data)) stop()
>         return(mean(data))
> }
>
> visit.level <- function(data, depth) {
>         if (depth == 2) {
>                 return(leaf.func(data))
>         } else {
>                 res <- lapply(data, visit.level, depth + 1)
>                 names(res) <- names(data)
>                 return(res)
>         }
> }
>
> new.data <- visit.level(data, 0)
> # ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
>
>
> Thanks,
> Giovanni
>
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