Nested list to data frame and back to nested list

Question

Consider a nested list with data that is basically rectangular.

mylst1 <- list(
  "system" = list(
    "subjectId" = c(101,102,103),
    "procedureId" = c(202,202,203)
  ),
  "demographics" = list(
    "demo_age" = c(12,22,32),
    "demo_gender" = c(1,0,1)
  ),
  "items" = list(
    "N" = list(
      "n001" = c(1,2,3),
      "n002" = c(3,2,1)
      ),
    "E" = list(
      "e001" = c(1,2,3),
      "e002" = c(3,2,1)
    )
  )
)

Since nested lists are awkward to work with, let's create a data frame: myDf <- data.frame(mylst1)

So far so good, now I can perform all my operations on myDf. Let's assume i just filtered some observations. The problem is that I need to return the same nested list structure as required by the web application I want to send this data to, but now the data of course looks like this:

> str(myDf)    
'data.frame':   3 obs. of  8 variables:
     $ system.subjectId        : num  101 102 103
     $ system.procedureId      : num  202 202 203
     $ demographics.demo_age   : num  12 22 32
     $ demographics.demo_gender: num  1 0 1
     $ items.N.n001            : num  1 2 3
     $ items.N.n002            : num  3 2 1
     $ items.E.e001            : num  1 2 3
     $ items.E.e002            : num  3 2 1

What would be the best solution to get this data in the original list format? I was thinking of using the . as a delimiter for each level, but i'm unsure how to do this in practice.

Thanks

akrun · Accepted Answer · 2017-08-14 15:23:32Z

3

One option would be relist (assuming that the columns are all of the same class) as in the 'myDf'

newlst <- relist(unlist(myDf), skeleton = mylst1)
identical(mylst1, newlst)
#[1] TRUE

answered Aug 14, 2017 at 15:23

akrun

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3 Comments

lmo Over a year ago

One major caveat (I believe) is that the number of elements in myDF cannot change (no added or removed rows). A second potential issue is that unlist will coerce all elements to the same type.

akrun Over a year ago

@lmo Yeah that is right, and i added the assumption about the same class

Comfort Eagle Over a year ago

Thank you! I didn't know about relist()! As lmo pointed out, the problem is that i now cannot add or remove cases. Is there a work around here?

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