Add an expression to convert an array of pairs to an object

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    • Type: New Feature
    • Resolution: Done
    • Priority: Major - P3
    • 3.4.4, 3.5.5
    • Affects Version/s: None
    • Component/s: Aggregation Framework
    • None
    • Fully Compatible
    • v3.4
    • Query 2017-03-27
    • None
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      In many cases, it would be useful to construct an object from an array of key/value pairs. The new expression should be designed to work with the expression requested in SERVER-18794. For example, we could add an $arrayToObject expression, which could do the following:

      db.foo.drop();
db.foo.insert({
  myArray: [ ["price", 200], ["item", "mango"] ],
  document: {x: 1, y: 2, z: 2},
  docs: [
    {email: "charlie", count: 4, blah: "foo"},
    {email: "eliot", count: 500, blah: "bar"},
  ]
});
db.foo.aggregate([{
    $project: {
        convertedFrom2dArray: {$arrayToObject: "$myArray"},
        noOp: {$arrayToObject: {$objectToArray: "$document"}},
              aggregated: {$arrayToObject: {$zip: ["$docs.email", 
                                                   "$docs.count"]}}}
    }
}]);

// Output:
{
  _id: xxx,
  convertedFrom2dArray: {"price": 200, "item": "mango"},
  noOp: {x: 1, y: 2, z: 2},
  aggregated: {charlie: 4, eliot: 500},
}

      The expression should accept an array of pairs either represented as

      1. an array of two-element arrays (like [ ["price", 200], ["item", "mango"] ] above), or
      2. an array of two-field objects with key names k and v.

      In the latter case, the expression would permit conversion of [{k: "price", v: 200}, {k: "item", v: "mango"}] to {price: 200, item: "mango"}.

            Assignee:
            Tess Avitabile (Inactive)
            Reporter:
            Charlie Swanson
            Votes:
            6 Vote for this issue
            Watchers:
            14 Start watching this issue

              Created:
              Updated:
              Resolved: