I have an array like this :

const myArray = [ 
  {
    title: 'title',
    category: 'genetic-diseases'
  },
  {
    title: 'title',
    category: 'genetic-disorders'
  },
  { title: 'title', category: 'genetic-disorders' },
  {
    title: 'title',
    category: 'genetic-disorders'
  },
  {
    title: 'title',
    category: 'genetic-mutation'
  },
  {
    title: 'title',
    category: 'genetic-mutation'
  },
  {
    title: 'title',
    category: 'genetic-mutation'
  }
]

I only want two of each of category object in the array and remove the rest If the number of objects of that category is over 2 and get something like this :

const myArray = [ 
  {
    title: 'title',
    category: 'genetic-diseases'
  },
  { title: 'title', category: 'genetic-disorders' },
  {
    title: 'title',
    category: 'genetic-disorders'
  },
  {
    title: 'title',
    category: 'genetic-mutation'
  },
  {
    title: 'title',
    category: 'genetic-mutation'
  }
]

How can I remove the rest of the objects of a specific category If the number of those objects in the array is over 2 ?

CodePudding user response：

    const myArray = [ 
    {
    title: 'title',
    category: 'genetic-diseases'
    },
    {
    title: 'title',
    category: 'genetic-disorders'
    },
    { title: 'title', category: 'genetic-disorders' },
    {
    title: 'title',
    category: 'genetic-disorders'
    },
    {
    title: 'title',
    category: 'genetic-mutation'
    },
    {
    title: 'title',
    category: 'genetic-mutation'
    },
    {
    title: 'title',
    category: 'genetic-mutation'
    }
    ];
    
    var categoryQuantities = {}; //counts how many objects from each category entered the filtered array
    var filteredArray = []; //array with first 2 objects from each categoty
    for (var obj of myArray) {
        var category = obj.category;
        if (category in categoryQuantities) {
            categoryQuantities[category]  ;
        } else {
            categoryQuantities[category] = 1;
        }
        
        if (categoryQuantities[category] <= 2) {
            filteredArray.push(obj);
        }
    }
    
    console.log(filteredArray);

The final array is in 'filteredArray'. The original array is not changed, so you may want to do the following:

    myArray = filteredArray;

CodePudding user response：

Basically I did 2 phases. First I group by category (at most 2 items per category), then I flatten it. I made it into a general function called group_by_at_most

var myArray = get_data();

var result = group_by_at_most(myArray, 'category', 2);
console.log(result);

function group_by_at_most(myArray, by, at_most) {
  var obj = {}

  myArray.forEach(function(item) {
    if (!obj[item[by]]) {
      obj[item[by]] = []
    }
    if (obj[item[by]].length < at_most) {
      obj[item[by]].push(item);
    }
  })

  var result = [];
  for (var key in obj) {
    var items = obj[key];
    result.push(...items);
  }

  return result;
}



function get_data() {
  return [{
      title: 'title',
      category: 'genetic-diseases'
    },
    {
      title: 'title',
      category: 'genetic-disorders'
    },
    {
      title: 'title',
      category: 'genetic-disorders'
    },
    {
      title: 'title',
      category: 'genetic-disorders'
    },
    {
      title: 'title',
      category: 'genetic-mutation'
    },
    {
      title: 'title',
      category: 'genetic-mutation'
    },
    {
      title: 'title',
      category: 'genetic-mutation'
    }
  ]
}

.as-console-wrapper {
  max-height: 100% !important;
}