Bdtjtk

I have an array of arrays of objects which looks like this:

let fruitSamples = [

  [

    {'id': 1,'type': 'apples','samples': [1, 2, 3]},

    {'id': 2,'type': 'bananas','samples': [1, 2, 7]},

    {'id': 3,'type': 'pears','samples': [1, 2, 3]}

  ],

  [

    {'id': 1,'type': 'apples','samples': [5, 2, 9]},

    {'id': 2,'type': 'bananas','samples': [1, 7, 7]},

    {'id': 3,'type': 'pears','samples': [12, 21, 32]}

  ],

  [

    {'id': 1,'type': 'apples','samples': [11, 2, 33]},

    {'id': 2,'type': 'bananas','samples': [17, 2, 67]},

    {'id': 3,'type': 'pears','samples': [91, 22, 34]}

  ]

];

I want to reduce and merge the above array using lodash into one so that the samples get concatenated together like so:

fruitSamples = [

  {'id': 1, 'type': 'apples', 'samples': [1,2,3,5,2,9,11,2,33]},

  {'id': 2, 'type': 'bananas', 'samples': [1,2,7,1,7,7,17,2,67]},

  {'id': 3, 'type': 'pears', 'samples': [1,2,3,12,21,32,91,22,34]},

]

I have tried many different approaches but since I want the shortest possible way of solving this what would be your recommendations?

I have tried this:

let test = _(fruitSamples)

  .flatten()

  .groupBy('type')

  .map(_.spread(_.merge))

  .value();



console.log(test);

This gives me the following result, which does not concatenate the samples:

test = [

  {'id': 1,'type': 'apples','samples': [11, 2, 33]},

  {'id': 2,'type': 'bananas','samples': [17, 2, 67]},

  {'id': 3,'type': 'pears','samples': [91, 22, 34]}

]

I feel using _.mergeWith might be the right answer, if so, I am looking for help implementing mergeWith in the best possible way as I am not sure how to do it. Any suggestions?

Instead of _.merge, you could try using _.mergeWith that accepts a customizer function which you can use to customize the assigned values.

From the official docs:

This method is like _.merge except that it accepts customizer which is
invoked to produce the merged values of the destination and source
properties.

let fruitSamples = [

  [

    {'id': 1,'type': 'apples','samples': [1, 2, 3]},

    {'id': 2,'type': 'bananas','samples': [1, 2, 7]},

    {'id': 3,'type': 'pears','samples': [1, 2, 3]}

  ],

  [

    {'id': 1,'type': 'apples','samples': [5, 2, 9]},

    {'id': 2,'type': 'bananas','samples': [1, 7, 7]},

    {'id': 3,'type': 'pears','samples': [12, 21, 32]}

  ],

  [

    {'id': 1,'type': 'apples','samples': [11, 2, 33]},

    {'id': 2,'type': 'bananas','samples': [17, 2, 67]},

    {'id': 3,'type': 'pears','samples': [91, 22, 34]}

  ]

];



function customizer(objValue, srcValue) {

  if (_.isArray(objValue)) {

    return objValue.concat(srcValue);

  }

}



let test = _(fruitSamples)

  .flatten()

  .groupBy('type')

  .map(_.spread((...values) => {

    return _.mergeWith(...values, customizer);

  }))

  .value();

  

console.log(test);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>

Not sure how to do using lodash, but pure Javascript it's not too difficult.

Update: Thanks to @Taki doing a flat() first makes this even
easier..

let fruitSamples = [[{"id":1,"type":"apples","samples":[1,2,3]},{"id":2,"type":"bananas","samples":[1,2,7]},{"id":3,"type":"pears","samples":[1,2,3]}],[{"id":1,"type":"apples","samples":[5,2,9]},{"id":2,"type":"bananas","samples":[1,7,7]},{"id":3,"type":"pears","samples":[12,21,32]}],[{"id":1,"type":"apples","samples":[11,2,33]},{"id":2,"type":"bananas","samples":[17,2,67]},{"id":3,"type":"pears","samples":[91,22,34]}]];



let concat = fruitSamples.flat().reduce((a, i) => {

  const f = a.find(f => f.id === i.id);

  if (!f) a.push(i);

  else f.samples = [...f.samples, ...i.samples];

  return a;

}, );



console.log(concat);

You can first convert the array or arrays to simple array using .reduce and then group by using .reduce again.

May be more easy to grab

Something like

let fruitSamples = [

  [

    {'id': 1,'type': 'apples','samples': [1, 2, 3]},

    {'id': 2,'type': 'bananas','samples': [1, 2, 7]},

    {'id': 3,'type': 'pears','samples': [1, 2, 3]}

  ],

  [

    {'id': 1,'type': 'apples','samples': [5, 2, 9]},

    {'id': 2,'type': 'bananas','samples': [1, 7, 7]},

    {'id': 3,'type': 'pears','samples': [12, 21, 32]}

  ],

  [

    {'id': 1,'type': 'apples','samples': [11, 2, 33]},

    {'id': 2,'type': 'bananas','samples': [17, 2, 67]},

    {'id': 3,'type': 'pears','samples': [91, 22, 34]}

  ]

];



var merged = fruitSamples.reduce(function(prev, next) {

  return prev.concat(next);

});



var res = merged.reduce(function(prev, next) {

      

      var index = prev.findIndex(o=> o.id == next.id) 

         if(index >= 0)

           prev[index].samples = [...prev[index].samples,...next.samples];

           else

           prev.push(next);

           

           return prev;

},);



console.log(res)

One way to do it with javascript and no lodash:

var fruitSamples = [

[

   {'id': 1,'type': 'apples','samples': [1, 2, 3]},

   {'id': 2,'type': 'bananas','samples': [1, 2, 7]},

   {'id': 3,'type': 'pears','samples': [1, 2, 3]}

],

[

   {'id': 1,'type': 'apples','samples': [5, 2, 9]},

   {'id': 2,'type': 'bananas','samples': [1, 7, 7]},

   {'id': 3,'type': 'pears','samples': [12, 21, 32]}

],

[

   {'id': 1,'type': 'apples','samples': [11, 2, 33]},

   {'id': 2,'type': 'bananas','samples': [17, 2, 67]},

   {'id': 3,'type': 'pears','samples': [91, 22, 34]}

 ]

 ];



var test = fruitSamples.flat().reduce((rv,x)=>{

  var f = rv.find(y => y.id == x.id);

  if(f == null){

        f ={"id":x.id, "type":x.type,"samples":x.samples};

        rv.push(f);

  }

  else{

     f.samples = f.samples.concat(x.samples);

  }

  return rv;

},);

console.log(JSON.stringify(test))

https://jsfiddle.net/pimboden40/y8x96sbg/1/