MapReduce 与 MongoDB

Question

I have a document like this on MongoDB:

[
    {
        "option": "My fav food is pizza",
        "person": {
            "id": 1,
            "name": "John"
        },
        "location": {
            "country": "UK",
            "europe": "N"
        }
    },
    {
        "option": "I love football",
        "person": {
            "id": 2,
            "name": "Jack"
        },
        "location": {
            "country": "UK",
            "europe": "N"
        }
    }
]

And I have to obtain something like this, using MapReduce:

{
    "country": "UK",
    "value": {
        "count": 2,
        "sentences": [
            "I love football",
            "My fav food is pizza"
        ],
        "people": [
            "Jack",
            "John"
        ]
    }
}

The problem is that I have to deal with it using MapReduce (map, reduce and finalize) on Javascript and I am a little bit stuck on it.

I can't find any good examples as hard as this...

I would appreciate any help :)

Answer 1

we can write a reducer here to create a new object from the array.

The below code is an illustration of such an implementation

 const dataEntity = [ { "option": "My fav food is pizza", "person": { "id": 1, "name": "John" }, "location": { "country": "UK", "europe": "N" } }, { "option": "I love football", "person": { "id": 2, "name": "Jack" }, "location": { "country": "UK", "europe": "N" } } ]; let items = 0; let sentences = []; let people = []; const transformedObject = dataEntity.reduce((acc, curr)=>{ debugger; items+=1; sentences.push(curr.option); people.push(curr.person.name); acc["country"]=curr.location.country; if(!acc["value"]){ acc["value"]={}; } acc["value"]["count"] = items; acc["value"]["sentences"]=sentences; acc["value"]["people"]=people; return acc; },{}) console.log(transformedObject);

This is a simple illustration. You can further modify this snippet to fit the requirements.

Cheers.