looping nested lists in R

Question

I have a huge nested list of 15 levels. i need to replace empty lists occurring at any level with chr "". I tried lapply to loop through the list but it's not working. is there any easy way to do this?

nested_list<-list(a=list(x=list(),y=list(i=list(),j=list(p=list(),q=list()))),b=list())

lapply(nested_list,function(x) if(length(x)==0) "" else x)

the lapply is being applied to only first level, how do i recursively loop the entire nested list and perform this action?

Randy Lai · Accepted Answer · 2015-04-23 09:20:08Z

13

Try the following recursion.

foo <- function(l){
    lapply(l, function(x) if(length(x)==0) "" else foo(x))
}
foo(nested_list)

EDIT: A better version

foo <- function(l){
    lapply(l, function(x) if(is.list(x) && length(x)==0) "" else if(is.list(x)) foo(x) else x)
}

answered Apr 23, 2015 at 9:20

Randy Lai

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2 Comments

user1981275 Over a year ago

similar, but the other way around: myf = function(x) if (length(x)>0){lapply(x, myf)} else {if(length(x)==0) "" else x} and lapply(nested_list, myf)

JHS Over a year ago

Thanks guys! calling the function inside same function.. never thought of that :)

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