CODEWITHSUNDEEP
rlistmultidimensional-array
stepthom
stepthom

Reputation: 1462

Select wildcard in multidimensional list?

In R, I have a multidimensional list. I can access elements like:

results[["A1"]][["B2"]][["C1"]]

Of course, the output of the above statement is also a list.

What I'd like to do is something like:

results[["A1"]][[*]][["C1"]]

or 

results[["A1"]][[,]][["C1"]]

My desired output would be one big list, which is the concatenation of the lists for each value (e.g., "B1", "B2", ...) in the second dimension.

Is something like this possible? I know that I can iterate over the desired dimension:

for (i in 1:length(results[["A1"]])){
    output = c(output, results[["A1"]][[i]][["C1"]]
}

but I was wondering if there's anything cleaner? Am I doing it all wrong?

Upvotes: 0

Views: 752

Answers (1)

IRTFM
IRTFM

Reputation: 263451

Does this work?

sapply( sapply(results[["A1]], "[[", TRUE), "[[", "C1"")

The generalization to a fourth level for a specific index name "D" would just be:

sapply( sapply( sapply(results[["A1"]], "[[", TRUE), "[[", "C1"), "[[", "D")

Reading from the inside out, as one needs to do with nested function calls, all of sublists of the results$A1 values are collected and then processed to construct a list of only those with "C1" names, and then that reduced list is further extracted from to yield values of the form results$A1$all-wildcards$C1$D. Given the fact that the "[[" function will evaluate its argument you could have offer an unquoted object that had multiple values if they were valid list names at the appropriate level of indexing.

Upvotes: 1

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