How to do the array to array shift

[JeffSG]

hi there,

Could anyone help to show me how to do an array to array shift?
For example, the input Json is

{
  "students": [
    {"id":"1", "score":"5"},
    {"id":"2", "score":null}
  ]
}

And the expected output Json is

{
  "level1": {
    "level2": [
      {"number":"1", "score":"5"},
      {"number":"2", "score":null}
    ]
  }
}

How to write the shiftr spec?

Furthermore, is it possible to output only array element of which "score" is not null?

Thanks in advance.

Regards,
Jeff

[milosimpson]

You have to do two shifts.

First one, passes thru only the "students" with a non-null score. The second one, then does the "id" -> "number" transform.

[
  {
    "operation": "shift",
    "spec": {
      "students": {
        "*": {
          "score": {
            "null": null,
            "*": {
              "@(2)": "level1.level2[]"
            }
          }
        }
      }
    }
  },
  {
    "operation": "shift",
    "spec": {
      "level1": {
        "level2": {
          "*": {
            "id": "level1.level2[&1].number",
            "score": "level1.level2[&1].score"
          }
        }
      }
    }
  }
]

[JeffSG]

hi milosimson, thanks for the reply.
About the first "filter" shift, still have one question.

This time the input is

{
  "SolarSystem": {
      "Planet": [
      {
        "Satellite": {
          "PhysicalData": {
            "pd1": "pdv1",
            "pd2": "pdv2"
          },
          "ChemicalData": {
            "cd1": "cdv1",
            "cd2": "cdv2"
          }
        },
        "Name": "Earth"
      },
      {
        "Name": "Mercury",
        "Satellite": null
      }
    ]
  }
}

And the expected output is

[ {
  "Satellite" : {
    "PhysicalData" : {
      "pd1" : "pdv1",
      "pd2" : "pdv2"
    },
    "ChemicalData" : {
      "cd1" : "cdv1",
      "cd2" : "cdv2"
    }
  },
  "Name" : "Earth"
}]

Say, only keep the array element with non-null "Satellite"
I wrote the below spec

[
  {
    "operation": "shift",
    "spec": {
      "*": {
        "Planet": {
          "*": {
            "Satellite": {
              "null": null,
              "*": {
                "@(2)": "[]"
              }
            }
          }
        }
      }
    }
  }
]

The filter works. However, I got below output with duplicated elements (The repeating number is the key number under satellite).

[ {
  "Satellite" : {
    "PhysicalData" : {
      "pd1" : "pdv1",
      "pd2" : "pdv2"
    },
    "ChemicalData" : {
      "cd1" : "cdv1",
      "cd2" : "cdv2"
    }
  },
  "Name" : "Earth"
}, {
  "Satellite" : {
    "PhysicalData" : {
      "pd1" : "pdv1",
      "pd2" : "pdv2"
    },
    "ChemicalData" : {
      "cd1" : "cdv1",
      "cd2" : "cdv2"
    }
  },
  "Name" : "Earth"
} ]

Could you please help point out what the issue is in my spec?
Thank you.

[milosimpson]

Huh, looks like you found a legit bug. Usually, the filtering for "null" thing is either a null or a String, not a Map like Satellite.

[milosimpson]

Actually, no. Its working as intended. The problem is that when Satellite is not null, the "*" logic recurses down into the Satellite object, which has two entries "PhysicalData" and "ChemicalData" each of which trigger a copy.

The fix to change the first spec from looking for a "null", to looking for a Satellite that has a sub-object, like "PhysicalData".

Spec

[
  {
    "operation": "shift",
    "spec": {
      "Planet": {
        "*": {
          "Satellite": {
            "PhysicalData": {
              // @2 means look up the tree three levels (0, 1, 2), grab what is there (the whole planet object)
              // and then use that as the data to write to "PlanetsWithMoons"
              "@2": "PlanetsWithMoons"
            }
          }
        }
      }
    }
  }
]

[JeffSG]

Thank you very much Milo. It works now. Fantastic tool :)