I've read this and this and this but explanations are pretty scarce. I understand what "&" means. But I can't wrap my head around what [&] means =\

Can someone please explain me what this [&] does applicable to this example? What exactly happening in lines

"@1": "outer[&4].inner[&2].t",
"@(3,eventTypeCode)": "outer[&4].inner[&2].etc"

Input JSON :

{
  "uID": 1000358546,
  "events": [
    {
      "eventTypeCode": "FEEDBACK",
      "transports": [
        "PUSH",
        "SMS"
      ]
    },
    {
      "eventTypeCode": "MARKETING",
      "transports": [
        "PUSH",
        "EMAIL"
      ]
    },
    {
      "eventTypeCode": "ORDER_STATUS",
      "transports": [
        "SOC_VK"
      ]
    }
  ]
}

Spec :

[
  {
    "operation": "shift",
    "spec": {
      "events": {
        "*": {
          "transports": {
            "*": {
              "*": {
                "@1": "outer[&4].inner[&2].t",
                "@(3,eventTypeCode)": "outer[&4].inner[&2].etc"
              }
            }
          }
        }
      },
      "*": "&"
    }
  }
]

Result :

{
  "uID": 1000358546,
  "outer": [
    {
      "inner": [
        {
          "t": "PUSH",
          "etc": "FEEDBACK"
        },
        {
          "t": "SMS",
          "etc": "FEEDBACK"
        }
      ]
    },
    {
      "inner": [
        {
          "t": "PUSH",
          "etc": "MARKETING"
        },
        {
          "t": "EMAIL",
          "etc": "MARKETING"
        }
      ]
    },
    {
      "inner": [
        {
          "t": "SOC_VK",
          "etc": "ORDER_STATUS"
        }
      ]
    }
  ]
}

CodePudding user response：

Just count the single colon(colon without opening curly brace) along with the other opening curly braces while going the tree up(from inner to outer) for any wildcard such as @,$,&,[&]. Only difference among & and [&] is the second one tries to build an array while the first one replicates the respective value of the targeted level. So, [&] would do nothing(doesn't build an array) whenever the ampersand fully points out null values unlike to &

A side note : key[&] yields (with/without a dot after key) key name of the array while key& yields a simple concatenation (prefixing the respective value of &)

Let me try to explain using this spec :

[
  {
    "operation": "shift",
    "spec": {
      "events": {
        "*": {
          "transports": {
            "*": {
              "*": {
                "@1": "@(4,eventTypeCode).[&2]"
              }
            }
          }
        }
      }
    }
  }
]

you'd get the result

{
  "FEEDBACK" : [ "PUSH", "SMS" ],
  "MARKETING" : [ "PUSH", "EMAIL" ],
  "ORDER_STATUS" : [ "SOC_VK" ]
}

by using the above spec.

but it would yield

{
  "FEEDBACK" : {
    "0" : "PUSH",
    "1" : "SMS"
  },
  "MARKETING" : {
    "0" : "PUSH",
    "1" : "EMAIL"
  },
  "ORDER_STATUS" : {
    "0" : "SOC_VK"
  }
}

• if [&2] is replaced with &2. Since, both reaches to the same level(the level of the indices of "transports" through counting 0->[traversing single colon], 1->[traversing opening curly brace], 2->[traversing opening curly brace] ), one makes array while the other reveals the values of the indices as 0,1. Think a reciprocally changing for the represented values by "@1" and "@(4,eventTypeCode)"(right hand side one goes left while left hand side one goes right) -> @1 picks the values of the indices of "transports"(traversing opening curly brace twice by counting 0,1[if it was @[meaning @0] would traverse { once by counting only 0).

• if [&2] is replaced with &, then the output would be replicating the values coming from @1; while if [&2] is replaced with [&], then there would yield only a null because the innermost node has only nulls.