Combining items with nested Map structures

Question

Combining items with nested Map structures

I am in need of merging multiple JavaScript objects recursively. These objects contain number properties that need to be added together during the merge process. Additionally, they also have Map properties. Below is an example of how my object appears in the Developer Console:

byGender:Map
    0:{"Male" => 9}
        key:"Male"
        value:9
    1:{"Female" => 11}
        key:"Female"
        value:11
byType:Map
    0:{"Teens" => Object}
        key:"Teens"
        value:Object
            byGender:Map
                0:{"Guys" => 7}
                    key:"Guys"
                    value:7
                1:{"Girls" => 10}
                    key:"Girls"
                    value:10
            total:17
    1:{"Chaperones" => Object}
        key:"Chaperones"
        value:Object
            byGender:Map
                0:{"Ladies" => 1}
                    key:"Ladies"
                    value:1
                1:{"Men" => 2}
                    key:"Men"
                    value:2
            total:3
total:42

My goal is to merge these Map objects and add the numbers of matching keys together.

I'm currently using _.mergeWith along with a customizer function. While I am able to merge simple number properties successfully, I am facing difficulty in merging the Map objects as well. Currently, my customizer merger function replaces the Map object, causing the last one to overwrite the previous. Here's the customizer function I am using with _.mergeWith:

var merger = function (a, b) {
    if (_.isNumber(a)) {
      return a + b;
    } else {
      return _.mergeWith(a, b, merger);
    }
};

Searching for solutions has been challenging because the keyword "map" mainly returns results related to .map(), rather than focusing on the Map object itself.

javascript merge lodash

Answer 1

Answer №1

After much trial and error, I finally developed a merger function that gets the job done. While it may not be as sleek as I initially envisioned, I decided to share it here just in case anyone else is grappling with a similar issue.

Admittedly, the drawback of my solution is its lack of versatility. It seems to be tailored to a specific set of structures and recursion complexities, which could pose challenges when adapting it for different scenarios.

function merger(source, mergeTarget) {
    if (_.isNumber(source)) {
      return source + mergeTarget;
    } 
    else if (_.isMap(source)) {
        var newMap = new Map();
        source.forEach(function(value,key,root){
            var newValue = mergeTarget.get(key);
            if(_.isNumber(value))
                newMap.set(key,value + newValue);
            else if (_.isObject(value)){
                var newObj = {};
                _.mergeWith(newObj,value,newValue,merger);
                newMap.set(key,newObj);
            }
        });
        return newMap;
    }
 }

Answer 2

After much trial and error, I finally developed a merger function that gets the job done. While it may not be as sleek as I initially envisioned, I decided to share it here just in case anyone else is grappling with a similar issue.

Admittedly, the drawback of my solution is its lack of versatility. It seems to be tailored to a specific set of structures and recursion complexities, which could pose challenges when adapting it for different scenarios.

function merger(source, mergeTarget) {
    if (_.isNumber(source)) {
      return source + mergeTarget;
    } 
    else if (_.isMap(source)) {
        var newMap = new Map();
        source.forEach(function(value,key,root){
            var newValue = mergeTarget.get(key);
            if(_.isNumber(value))
                newMap.set(key,value + newValue);
            else if (_.isObject(value)){
                var newObj = {};
                _.mergeWith(newObj,value,newValue,merger);
                newMap.set(key,newObj);
            }
        });
        return newMap;
    }
 }

Answer 3

Answer №2

While it may seem like this information is coming in a bit late, there's still value in sharing it for others who might benefit:

If you're looking to merge Maps, there's a simple method that can be used:

const mergedMap = new Map([...map1, ...map2]);

If you need to handle conflicting values during the merge process, consider using the mapCollectInto function from the big-m library created specifically for this purpose (source code):

const { mapCollectInto, reconcileAdd } = "big-m";

const mergedMap = mapCollectInto(
  map1,
  map2,
  reconcileAdd()
);

Another option, without modifying map2:

const { mapCollect, mapConcat, reconcileAdd } = "big-m";

const mergedMap = mapCollect(
  mapConcat(map1, map2),
  reconcileAdd()
);

Answer 4

While it may seem like this information is coming in a bit late, there's still value in sharing it for others who might benefit:

If you're looking to merge Maps, there's a simple method that can be used:

const mergedMap = new Map([...map1, ...map2]);

If you need to handle conflicting values during the merge process, consider using the mapCollectInto function from the big-m library created specifically for this purpose (source code):

const { mapCollectInto, reconcileAdd } = "big-m";

const mergedMap = mapCollectInto(
  map1,
  map2,
  reconcileAdd()
);

Another option, without modifying map2:

const { mapCollect, mapConcat, reconcileAdd } = "big-m";

const mergedMap = mapCollect(
  mapConcat(map1, map2),
  reconcileAdd()
);

Combining items with nested Map structures

Answer №1

Answer №2

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