Eliminate repetitive elements from an array using a specific merging algorithm

Here's a thought I have:

If we have an array of objects like this:

[
    {
        "name": "Kirk",
        "count": 1
    },
    {
        "name": "Spock",
        "count": 1
    },
    {
        "name": "Kirk",
        "count": 1
    }
]

I would like to achieve this result:

[
    {
        "name": "Kirk",
        "count": 2
    },
    {
        "name": "Spock",
        "count": 1
    }
]

I am interested in finding an algorithm that could potentially leverage higher order functions for this task. While using loops is possible, my goal is to explore more elegant solutions with higher order functions. Any guidance on the specific methods or techniques I should consider for this problem would be greatly appreciated. My preference is for a solution that is as concise and expressive as possible (avoiding complex combinations of maps and filters).

This is my current approach, but I believe there may be room for improvement:

function mergeDuplicates(input) {
  var output = [];
  var existingItem = null;
  input.forEach(function (inputItem) {
    existingItem = _.find(output, function (outputItem) {
      return inputItem.name === outputItem.name;
    });
    existingItem ? existingItem.count += 1 : output.push({
      name: inputItem.name,
      count: 1
    });
    existingItem = null;
  });
  return output;
}

Just to clarify line #10: if the original array has no 'count' property or it is initially set to 1, I default it to 1.

Answer №1

In my opinion, a effective approach would involve hashing each object if it is not already hashed, then removing the ones that have already been hashed in your data structure. This method allows you to verify the existence of each object with just one check (depending on how your hash scheme works).

Answer №2

Here is a handy function that you can utilize.

function combineArrays(arr) {    
   for(var obj = {}, item; item = arr.shift(); obj[item.name] = item.count + (obj[item.name] || 0));
   for(item in obj) arr.push({name: item, count: obj[item]});
}

Example of how to use this function:

var teamMembers = [{"name":"Michael","count":1},
               {"name":"Dwight","count":1},
               {"name":"Michael","count":1}];

combineArrays(teamMembers);   

// teamMembers array now looks like:  [{"name":"Michael","count":2}, {"name":"Dwight","count":1}]

Answer №3

If you're looking to transform an array using a method similar to fold, consider utilizing the reduce function in JavaScript.

a.reduce(function(previousValue, currentValue) {
        var name = currentValue.name;
        if (previousValue[name]) {
            previousValue[name].count++;
        } else {
            previousValue[name] = currentValue;
        }
        return previousValue;
    }, {})

You will end up with an object containing "Kirk" and "Spock" as keys, and their corresponding values based on your requirements.

Answer №4

Although this question is quite old, I couldn't resist the challenge of coming up with my own solution. Instead of using two maps and a filter, I opted for a sort followed by a reduce. It was quite enjoyable to work through this one :-)

function handleDuplicates(dataList, property, callback){
  return dataList.sort(function(a,b){
    if(a[property] < b[property]){ return -1;}
    if(a[property] > b[property]){return 1;}
    return 0;
  }).reduce(function(accumulator, item, index, array){
    if(index > 0 && array[index-1][property] === item[property]){
      callback(accumulator[accumulator.length-1], item);
      return accumulator;
    }else{
      var newEntry = Object.assign({}, item);
      callback(newEntry);
      accumulator.push(newEntry);
      return accumulator;
    }
  }, []);
}

This function can be used like so:

var updatedList = handleDuplicates(dataList, "name", function(item, duplicate){
    if(duplicate){
      item.count++;
    }else{
      item.count = 1;
    }        
});

Alternatively, here's another approach that utilizes 'Ramda' library in JavaScript. This version involves using reduce and employs an object as a hashmap to manage duplicates (similar to other solutions).

const mergeRepeatingEntries = (callback, property, list) => R.pipe(
  R.reduce((acc, item) => (
    R.has(item[property], acc) ?
      R.assoc(item[property], callback(acc[item[property]], item), acc) :
      R.assoc(item[property], callback(item), acc)     
  ), {}), 
  R.values
)(list);

const modifyCallback = (previousEntry, duplicate) => ( !R.isNil(duplicate) ? 
  R.assoc('count', previousEntry.count + 1, previousEntry) :
  R.assoc('count', 1, previousEntry) )

mergeRepeatingEntries(modifyCallback, 'name', items);

Feel free to try it out for yourself on Ramda's website.

Answer №5

Give this method a try, it is more efficient in resolving your problems.

improve(arrayOfObj, 'name');

function improve(arr, prop) {
  var new_arr = [];
  var lookup = {};
  for (var i in arr) {
   lookup[arr[i][prop]] = arr[i];
  }
  for (i in lookup) {
   new_arr.push(lookup[i]); 
  }
  return new_arr;
}

Answer №6

Here's a different approach utilizing the reduce function:

var items =
[
    {
        "name": "Kirk",
        "count": 1
    },
    {
        "name": "Spock",
        "count": 1
    },
    {
        "name": "Kirk",
        "count": 1
    }
];
    

var filtered = items.reduce(function(prev, current,index){ 
    if(!(current.name in prev.keys)) {
       prev.keys[current.name] = index;
       prev.result.push(current);
   } 
   else{
       prev.result[prev.keys[current.name]].count += current.count; 
   }
   return prev;
},{result: [], keys: []}).result;

    

document.getElementById("output").innerHTML = JSON.stringify(filtered,null,2);
<pre id='output' />

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