data.frame with hierarchy for nested list in R

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I have the following data.frame d : 

x <- data.frame(a=letters[1:3], b=letters[4:6], c=letters[7:9], stringsAsFactors=F)
d <- tidyr::expand(x)
d

Source: local data frame [27 x 3]

   a b c
1  a d g
2  a d h
3  a d i
4  a e g
5  a e h
6  a e i
7  a f g
8  a f h
9  a f i
10 b d g
11 b d h
12 b d i
13 b e g
14 b e h
15 b e i
16 b f g
17 b f h
18 b f i
19 c d g
20 c d h
21 c d i
22 c e g
23 c e h
24 c e i
25 c f g
26 c f h
27 c f i

I'd like to get a nested list like this (to work with JSON and stuff like that): 

$a
$a$d
[1] "g" "h" "i" "g" "h" "i" "g" "h" "i"
$a$e
[1] "g" "h" "i" "g" "h" "i" "g" "h" "i"
$a$f
[1] "g" "h" "i" "g" "h" "i" "g" "h" "i"

$b
$b$d
[1] "g" "h" "i" "g" "h" "i" "g" "h" "i"
$b$e
[1] "g" "h" "i" "g" "h" "i" "g" "h" "i"
$b$f
[1] "g" "h" "i" "g" "h" "i" "g" "h" "i"

$c
$c$d
[1] "g" "h" "i" "g" "h" "i" "g" "h" "i"
$c$e
[1] "g" "h" "i" "g" "h" "i" "g" "h" "i"    
$c$f
[1] "g" "h" "i" "g" "h" "i" "g" "h" "i"

To do this, I used the function tree below 

tree <- function(d) {
  aux <- with(d, split(b, list(a)))
  res <- lapply(aux, function(x) with(d, split(c, list(x))))
  res
}

Now, let's say I have a data.frame hierarchical with n columns. How do I create a nested list?

Thank you!

Related Questions

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asked by anonymous 22.01.2015 / 14:13

2 answers

5

A solution using recursion would be: 

rec_split <- function(df){
 if(ncol(df) == 2){
  l <- split(df[[2]], df[[1]])
 }else{
   l <- split(df[-1], df[[1]])
   lapply(l, rec_split)
 }
}

Example: 

rec_split(d)
$a
$a$d
[1] "g" "h" "i"
$a$e
[1] "g" "h" "i"
$a$f
[1] "g" "h" "i"

$b
$b$d
[1] "g" "h" "i"
$b$e
[1] "g" "h" "i"
$b$f
[1] "g" "h" "i"

$c
$c$d
[1] "g" "h" "i"
$c$e
[1] "g" "h" "i"
$c$f
[1] "g" "h" "i"
    
22.01.2015 / 23:07
4

Most of the process you've done. There is only one structure that allows recursively to the penultimate column (and the last would be a vector of the results, so I understood). This one here seemed like an ingenious solution to your problem: link 

library(plyr)

nested.dlply <- function(df, by, fun, ...) {
   if (length(by) == 1) {
      dlply(df, by, fun, ...)
   } else {
      dlply(df, by[1], nested.dlply, by[-1], fun, ...)
   }
}

x <- data.frame(a=letters[1:3], b=letters[4:6], c=letters[7:9], stringsAsFactors=F)
d <- tidyr::expand(x)

var.names <- names(d)
n <- length(var.names)
d.list <- nested.dlply(d, var.names[-n], function(x)x[, var.names[n]])

jsonlite::toJSON(d.list, pretty=TRUE) # Se quiser transformar num JSON

And the result is 

> d.list$a
$d
[1] "g" "h" "i"

$e
[1] "g" "h" "i"

$f
[1] "g" "h" "i"

You can improve the way you do this, for example in the above code I'm accessing an object outside the scope of the anonymous function that will return the last column to the nested list.

    
22.01.2015 / 19:15
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