Turns nested Lists into nested Associations, ReplaceAll for list vs ReplacsAll for association

Question

I want to transform some nested lists into nested associations except the "rows"->List pattern.

Here is the example

s={"sensor" -> {"opto" -> {"filename" -> 
      "137fb39d9a39f0e18ec49f4a68d72554_opto.csv", 
     "data" -> {"time" -> {"unit" -> "s", "rows" -> {1}}, 
       "4" -> {"unit" -> "intensity", "rows" -> {2, 3}}, 
       "1" -> {"unit" -> "intensity", "rows" -> {4, 5}}}}, 
   "qmb1" -> {"filename" -> 
      "137fb39d9a39f0e18ec49f4a68d72554_qmb1.csv", 
     "data" -> {"qmb1" -> {"unit" -> "intensity", "rows" -> {2}}, 
       "time" -> {"unit" -> "s", "rows" -> {1}}}}, 
   "saw" -> {"filename" -> "137fb39d9a39f0e18ec49f4a68d72554_saw.csv",
      "data" -> {"time" -> {"unit" -> "s", "rows" -> {1}}, 
       "15" -> {"unit" -> "Hz", "rows" -> {5, 6}}, 
       "10" -> {"unit" -> "Hz", "rows" -> {2, 3, 4}}, 
       "9" -> {"unit" -> "Hz", "rows" -> {7, 8, 9}}}}, 
   "qmb2" -> {"filename" -> 
      "137fb39d9a39f0e18ec49f4a68d72554_qmb2.csv", 
     "data" -> {"time" -> {"unit" -> "s", "rows" -> {1}}, 
       "qmb2" -> {"unit" -> "intensity", "rows" -> {2}}, 
       "flow" -> {"unit" -> "sscm", "rows" -> {4}}, 
       "temperature" -> {"unit" -> "\[Degree]C", "rows" -> {3}}, 
       "humidity" -> {"unit" -> "%", "rows" -> {5}}}}}, 
 "date" -> {"year" -> 2016, "month" -> 11, "sec" -> 10, "day" -> 17, 
   "hour" -> 14, "min" -> 18}, "serie" -> 1, 
 "compound" -> "multi-detection", "inLab" -> 0, "proto" -> 1, 
 "uuid" -> "137fb39d9a39f0e18ec49f4a68d72554"}

So far I have done:

ReplaceAll[s, List :> Association]

which gives

<|"sensor" -> <|"opto" -> <|"filename" -> 
      "137fb39d9a39f0e18ec49f4a68d72554_opto.csv", 
     "data" -> <|"time" -> <|"unit" -> "s", 
         "rows" -> Association[1]|>, 
       "4" -> <|"unit" -> "intensity", "rows" -> Association[2, 3]|>, 
       "1" -> <|"unit" -> "intensity", 
         "rows" -> Association[4, 5]|>|>|>, 
   "qmb1" -> <|"filename" -> 
      "137fb39d9a39f0e18ec49f4a68d72554_qmb1.csv", 
     "data" -> <|"qmb1" -> <|"unit" -> "intensity", 
         "rows" -> Association[2]|>, 
       "time" -> <|"unit" -> "s", "rows" -> Association[1]|>|>|>, 
   "saw" -> <|"filename" -> 
      "137fb39d9a39f0e18ec49f4a68d72554_saw.csv", 
     "data" -> <|"time" -> <|"unit" -> "s", 
         "rows" -> Association[1]|>, 
       "15" -> <|"unit" -> "Hz", "rows" -> Association[5, 6]|>, 
       "10" -> <|"unit" -> "Hz", "rows" -> Association[2, 3, 4]|>, 
       "9" -> <|"unit" -> "Hz", "rows" -> Association[7, 8, 9]|>|>|>, 
   "qmb2" -> <|"filename" -> 
      "137fb39d9a39f0e18ec49f4a68d72554_qmb2.csv", 
     "data" -> <|"time" -> <|"unit" -> "s", 
         "rows" -> Association[1]|>, 
       "qmb2" -> <|"unit" -> "intensity", "rows" -> Association[2]|>, 
       "flow" -> <|"unit" -> "sscm", "rows" -> Association[4]|>, 
       "temperature" -> <|"unit" -> "\[Degree]C", 
         "rows" -> Association[3]|>, 
       "humidity" -> <|"unit" -> "%", 
         "rows" -> Association[5]|>|>|>|>, 
 "date" -> <|"year" -> 2016, "month" -> 11, "sec" -> 10, "day" -> 17, 
   "hour" -> 14, "min" -> 18|>, "serie" -> 1, 
 "compound" -> "multi-detection", "inLab" -> 0, "proto" -> 1, 
 "uuid" -> "137fb39d9a39f0e18ec49f4a68d72554"|>

However I am stuck here, because ReplaceAll does not seem to work for Association as it works for List. By example:

ReplaceAll[Normal@<|"unit" -> "intensity","rows" -> Association[4, 5]|>, 
           ("rows" -> a_Association) :> ("rows" -> Apply[List, a])]

gives (as expected)

{"unit" -> "intensity", "rows" -> {4, 5}}

but

ReplaceAll[<|"unit" -> "intensity","rows" -> Association[4, 5]|>, 
           ("rows" -> a_Association) :> ("rows" -> Apply[List, a])]

has no effect

<|"unit" -> "intensity", "rows" -> Association[4, 5]|>

Questions

• why ReplaceAll does not work for Association?
• how to turns "rows"->Association[4,5,...] into "rows"->{4,5,...} in my association ("rows"->... can be at any place)

Note: I am using MMA v10

Answer 1

Note: This answers the question of how to achieve the specific replacement in the question and why the original attempt does not work. To do the actual conversion, it is better to use GeneralUtilities`ToAssociations, as mentioned in the comments, and the question linked there.

The problem is that keys of associations are invisible to most functions, similar to how you don't see indices in normal lists (you can think of the keys as named indices). To see this, consider:

<|"a" -> "a", "b" -> {"a", "b"}|> /. "a" -> "xx"
(* <|"a" -> "xx", "b" -> {"xx", "b"}|> *)

As you can see, the keys are not touched.

There are several ways to work around this:

• Use MapAt to transform the given entry. This will not work in all cases, but it is very clear in its intent.

  MapAt[Apply[List], "rows"]@<|"unit" -> "intensity", "rows" -> Association[4, 5]|>
  (* <|"unit" -> "intensity", "rows" -> {4, 5}|> *)
  

  You can also use Query to the same effect:

  Query[{"rows" -> Apply[List]}]@<|"unit" -> "intensity", "rows" -> Association[4, 5]|>
  (* <|"unit" -> "intensity", "rows" -> {4, 5}|> *)
  

• Use the second syntax of AssociationMap. This only works for the top-level association in its current form, but is otherwise very close in functionality:

  AssociationMap[
   Replace[("rows" -> a_Association) :> ("rows" -> Apply[List, a])],
   <|"unit" -> "intensity", "rows" -> Association[4, 5]|>
   ]
  
  <|"unit" -> "intensity", "rows" -> {4, 5}|>
  

• Match the whole association. This is pretty close to your original attempt, but has the disadvantage that the association can only be matched once, and it a bit harder to read. (this appears to only work starting with 11.0 or so)

  ReplaceAll[
   <|"unit" -> "intensity", "rows" -> Association[4, 5]|>,
   <|pre___, "rows" -> a_Association, post___|> :>
    <|pre, "rows" -> Apply[List, a], post|>
   ]
  (* <|"unit" -> "intensity", "rows" -> Association[4, 5]|> *)