JSON fields have the same name

Question

In practice, keys should be unique in a JSON object (for example, does JSON syntax allow duplicate keys in an object? ). However, suppose I have a file with the following contents:

{
    "a" : "1",
    "b" : "2",
    "a" : "3"
}

Is there an easy way to convert duplicate keys to an array? To make the file:

{
    "a" : [ {"key": "1"}, {"key": "3"}],
    "b" : "2"
}

Or something similar, but which combines duplicate keys into an array (or finds an alternative way to extract duplicate key values).

Here's the solution in Java: Converting a JSON object with duplicate keys into a JSON array

Is there a way to do this with awk / bash / python?

Answer 1

JSON , :

jq -s --stream 'group_by(.[0]) | map({"key": .[0][0][0], "value": map(.[1])}) | from_entries'

{
  "a": [
    "1",
    "3"
  ],
  "b": [
    "2"
  ]
}

, --stream , .

Answer 2

-s --stream, , :

reduce (.[] | select(length==2)) as $kv ({};
      $kv[0][0] as $k
      |$kv[1] as $v
      | (.[$k]|type) as $t
      | if $t == "null" then .[$k] = $v
        elif $t == "array" then .[$k] += [$v]
        else .[$k] = [ .[$k], $v ]
        end)

:

{
  "a": [
    "1",
    "3"
  ],
  "b": "2"
}

, , :

{
    "c" : "C",
    "a" : "1",
    "b" : "2",
    "a" : "3",
    "b" : "1"
}

, :

{
  "c": "C",
  "a": [
    "1",
    "3"
  ],
  "b": [
    "2",
    "1"
  ]
}

Answer 3

, slurp-Option (-).

This is not an answer to the original question, but since the jq-FAQ links here may be useful to some visitors

Jqmergekeys.txt file

def consumestream($arr): # Reads stream elements from stdin until we have enough elements to build one object and returns them as array
input as $inp 
| if $inp|has(1) then consumestream($arr+[$inp]) # input=keyvalue pair => Add to array and consume more
  elif ($inp[0]|has(1)) then consumestream($arr) # input=closing subkey => Skip and consume more
  else $arr end; # input=closing root object => return array

def convert2obj($stream): # Converts an object in stream notation into an object, and merges the values of duplicate keys into arrays
reduce ($stream[]) as $kv ({}; # This function is based on http://stackoverflow.com/a/36974355/2606757
      $kv[0] as $k
      | $kv[1] as $v
      | (getpath($k)|type) as $t # type of existing value under the given key
      | if $t == "null" then setpath($k;$v) # value not existing => set value
        elif $t == "array" then setpath($k; getpath($k) + [$v] ) # value is already an array => add value to array
        else setpath($k; [getpath($k), $v ]) # single value => put existing and new value into an array
        end);

def mainloop(f):  (convert2obj(consumestream([input]))|f),mainloop(f); # Consumes streams forever, converts them into an object and applies the user provided filter
def mergeduplicates(f): try mainloop(f) catch if .=="break" then empty else error end; # Catches the "break" thrown by jq if there no more input

#---------------- User code below --------------------------    

mergeduplicates(.) # merge duplicate keys in input, without any additional filters

#mergeduplicates(select(.layers)|.layers.frame) # merge duplicate keys in input and apply some filter afterwards

Example:

tshark -T ek | jq -nc --stream -f ./jqmergekeys.txt