How to merge/concatenate values of same object properties in an array of objects using lodash?

问题

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?

回答1:

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>

回答2:

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);

回答3:

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)

回答4:

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/

来源：https://stackoverflow.com/questions/54025657/how-to-merge-concatenate-values-of-same-object-properties-in-an-array-of-objects

标签

javascript

arrays

lodash

javascript-objects