Refactor: How to use .reduce with an external function?-CodePudding

hope that you're doing well. I've a question related to the .reduce function. I'm refactoring an elder code and, in order to fulfill the DRY principle, I'd like to know how to create a function that allows my to achieve a 'simple' process from .reduce:

Group the data by a certain key (phoNumbId in the example).
Sum values of another key (but related to the first key) to summarize both (this key is mount).
Return a dictionary with the grouped key and the added values

To clarify my question, I've this example dictionary:

const nexus = [
  { namesId: 1, phoNumbId: 1, country: 'PERU', mount: 1200 },
  { namesId: 1, phoNumbId: 2, country: 'CANADA', mount: 2000},
  { namesId: 2, phoNumbId: 2, country: 'ENGLAND', mount: 3000},
  { namesId: 2, phoNumbId: 3, country: 'RUSSIA', mount: 40000},
  { namesId: 3, phoNumbId: 1, country: 'BELGIUM', mount: 500},
  { namesId: 3, phoNumbId: 2, country: 'SPAIN', mount: 500},
  { namesId: 3, phoNumbId: 3, country: 'PORTUGAL', mount: 2020}
]

And the (coded) process that I want to refactor is:

var result2 = [];

nexus.reduce(function (res, value) {
        if (!res[value.phoNumbId]) {
            res[value.phoNumbId] = { phoNumbId: value.phoNumbId, mount: 0 };
            result2.push(res[value.phoNumbId])
        }
        res[value.phoNumbId].mount = value.mount;
        return res;
    }, {});

The way that my limited knowledge in JS allows me to code a possible solution then is as follows:

function sumAll(firstValue,secondValue,finalArray){
 if (!res[value.firstValue]) {
            res[value.firstValue] = { firstValue: value.firstValue, secondValue: 0 };
            finalArray.push(res[value.firstValue])
        }
        res[value.primerValor].secondValue = value.secondValue;
        return res;
}

var result2 = [];

nexus.reduce(function (res, value) { sumAll(phoNumbId,mount,result2) }, {});

I'd really appreciate anykind of help :) P.S.: I couldn't think of another title for the question, feel that doesn't summarize the real problem. I accept suggestions.

CodePudding user response：

You can use computed property names - that's using your argument values in bracket notation - to create the object.

const data=[{namesId:1,phoNumbId:1,country:"PERU",mount:1200},{namesId:1,phoNumbId:2,country:"CANADA",mount:2e3},{namesId:2,phoNumbId:2,country:"ENGLAND",mount:3e3},{namesId:2,phoNumbId:3,country:"RUSSIA",mount:4e4},{namesId:3,phoNumbId:1,country:"BELGIUM",mount:500},{namesId:3,phoNumbId:2,country:"SPAIN",mount:500},{namesId:3,phoNumbId:3,country:"PORTUGAL",mount:2020}];

function sumAll(data, first, second) {

  const temp = data.reduce((acc, c) => {
    
    // For convenience assign the object key
    // to the first argument
    const key = c[first];
    
    // If the key doesn't exist on the object
    // add it and assign an object to it
    acc[key] ??= { [first]: key, [second]: 0 };
    
    // Then update the value
    acc[key][second]  = c[second];
   
    return acc;
  
  }, {});
  
  // Finally you probably want to return
  // an array of just those objects
  return Object.values(temp);
  
}

console.log(sumAll(data, 'phoNumbId', 'mount'));
console.log(sumAll(data, 'namesId', 'mount'));

Additional documentation

CodePudding user response：

Consider your original code (before refactoring) is runnable.

Here is the first integration:

var result2 = nexus.reduce(function (res, value) {
    if (!res[value.phoNumbId]) {
        res[value.phoNumbId] = { phoNumbId: value.phoNumbId, mount: 0 };
        res.push(res[value.phoNumbId])
    }

    res[value.phoNumbId].mount  = value.mount;
    return res;
}, []);

What changed:

the return from the reduce function is assigned directly to result2
the 2nd param of the reduce function is the initial value of the result2 from the origin (in this case, an empty array [])
the result2.push(....) is changed to res.push(....)

Here is the second integration:

var result = nexus.reduce(function (acc, cur, origin) {
    if (!acc[cur.phoNumbId]) {
        acc[cur.phoNumbId] = { phoNumbId: cur.phoNumbId, mount: 0 };
        acc.push(acc[cur.phoNumbId])
    }

    acc[cur.phoNumbId].mount  = cur.mount;
    return acc;
}, []);

What changed:

rename variables:
- result2 -> result
- res -> acc (it stands for accumulator)
- value -> cur (it stands for current value)
add new param: origin

Here is the third integration

function my_reducer(acc, cur) {
    if (!acc[cur.phoNumbId]) {
        acc[cur.phoNumbId] = { phoNumbId: cur.phoNumbId, mount: 0 };
        acc.push(acc[cur.phoNumbId])
    }

    acc[cur.phoNumbId].mount  = cur.mount;
    return acc;
}

var result = nexus.reduce(my_reducer, []);

What changed:

Extract the no name function (the one that was passed as the 1st param to the reduce function) to a function with a name.

It will take time to explain the way the reduce function works. You can find out around the internet or other StackOverflow questions/answers.

Here is a short explanation:

Take a look at var result = nexus.reduce(my_reducer, []);, consider

result is an soup bow