Avoding nested for-loop for nested list

Question

I have a list, that is a string. In this string, the characters are separated by either a ";" or ",". So I have to use a "strsplit". With this, in this example, I end up with 3 list, where 2 of those lists have 3 elements and the last only will have 2 elements in the list.

mylist = c("ac*, be, cd*; daa, efae*, fge*; gefa*, h")
Liste <- strsplit(strsplit(mylist , ";")[[1]], ",")

The reason for, using "strsplit" like this, is that when I have a ";" in my string and "," as a logical OR, then it acts like a logical AND, that means I have to use one element from each list, later in my code.

So the output of Liste will be

[[1]]
[1] "ac*"  " be" " cd*"

[[2]]
[1] " daa" " efae*" " fge*"

[[3]]
[1] " gefa*" " h"

What I am trying to avoid, is the use of the double for-loop, and maybe make the code faster, if it is possible.

so now I am using a nested for-loop, to look at each element in mylist.

for (c in 1:length(Liste)){
  for (d in 1:length(Liste[[c]])){
    # Extracting last character, matching if it is a wildcard
    # Liste[[c]][d] Prints all elements from the list
    # I need the double for-loop for this check
    if (stri_sub(Liste[[c]][d],-1,-1) == '*')
        DO SOMETHING
  }
}

What else can be done here?

Nicolas2 · Accepted Answer · 2018-08-03 08:51:41Z

3

You can try:

library(purrr)
walk(unlist(Liste),
     function(x) if (stri_sub(x,-1,-1) == '*')
                   DO SOMETHING
     )

answered Aug 3, 2018 at 8:51

Nicolas2

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1 Comment

KaZyKa Over a year ago

This is working, but I am ending using @Florian's code :)

Florian · Accepted Answer · 2018-08-03 08:52:01Z

2

It of course depends on what you want to do in those cases, but it seems stri_sub is vectorized, so you could make use of that. For example, to return all elements that match your condition, you could do

lapply(Liste, function(x) {x[stri_sub(x,-1,-1)=='*']})

which outputs

[[1]]
[1] "ac*"  " cd*"

[[2]]
[1] " efae*" " fge*" 

[[3]]
[1] " gefa*"

Hope this helps!

answered Aug 3, 2018 at 8:52

Florian

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