Compared nested arrays with mongo

Question

I need to compare two nested arrays with mongo but I'm not really an expert so I need some help on doing that.

Let's say I have a document with an array slots:

[
    [
        {
            "start": 1,
            "end": 2
        }
    ],
    [
        {
            "start": 3,
            "end": 4
        },
        {
            "start": 5,
            "end": 6
        }
    ]
]

And I need to know if another array is a subset of it:

db.collection.aggregate([
  {
    $project: {
      slots: {
        $setIsSubset: [
          [
            [
              {
                start: 1,
                end: 2
              }
            ],
            [
              {
                start: 3,
                end: 4
              },
              {
                start: 5,
                end: 6
              }
            ]
          ],
          "$slots"
        ]
      }
    }
  }
])

This returns true, but if I remove one element in the second sub array, it returns false as the sub array isn't equal anymore.

I thought of doing some kind of $map where I would compare each sub array but I realized I didn't know how to reference the index of the array we're comparing to.

Any ideas? Thanks

Edit : the first level of the stored array and the array we're comparing it with are days of the week so that information needs to be kept.

Online sandbox

mickl · Accepted Answer · 2019-03-11 16:20:53Z

2

If you consider those nested arrays as days of week you probably need to compare them day by day and check if all "pairs" are subsets. To achieve that you can use $addFields to add your input as another field and then in the next step run $setIsSubset on every day based on index generated by $range operator. If all elements are true ($allElementsTrue) then it means that you specified a subset for every day:

var input = [
    [
        {
        start: 1,
        end: 2
        }
    ],
    [
        {
        start: 5,
        end: 6
        }
    ]
];

db.col.aggregate([
    {
        $addFields: {
            inputArray: input
        }
    },
    {
        $project: {
            isSubset: {
                $allElementsTrue: {
                    $map: {
                        input: { $range: [ 0, { $size: "$slots" } ] },
                        as: "index",
                        in: {
                            $setIsSubset: [
                                { $arrayElemAt: [ "$inputArray", "$$index" ] },
                                { $arrayElemAt: [ "$slots", "$$index" ] }
                            ]
                        }
                    }
                }
            }
        }
    }
])

edited Mar 11, 2019 at 16:20

answered Mar 11, 2019 at 15:50

mickl

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11 Comments

MrVoodoo Over a year ago

Sorry, should have mentioned I can't extract the arrays as their position is significant (it refers to a day of the week). I'll edit the OP.

mickl Over a year ago

@MrVoodoo so maybe you could keep slots as the original array but run $setIsSubset on flattened array just to check if subsets match ?

MrVoodoo Over a year ago

In some cases the check would pass even if it shouldn't. For example Monday has {start: 1, end: 2} and I want to check if Tuesday has {start: 1, end: 2}, it would pass the test.

mickl Over a year ago

@MrVoodoo I see, modfied my answer

Ashh Over a year ago

Why are you asking about that Actually one of my colleague has gotten two wonderful gift hampers(containing two mugs, t-shirts, bottles and much more) from the stackoverflow. She has participated in some contest on the stackoverflow I don't know much about that but she has. I read about that on metaexchange and learned that SO rewards that on 100k reps but she has only 1k. So I wanted to know whether I m missing something. BTW Thank you

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