How to loop and push on the accumulator of a reduce function?-CodePudding

I'm trying to reduce an array, and transform it in multiple array.

  const array = [
    { a: 1, b: 6 },
    { a: 1, b: 5 },
    { a: 1, b: 6 },
    { a: 1, b: 4 },
    { a: 1, b: 5 }
  ];

  var newArray = array.reduce(
    (memo, curr) => {
      memo.forEach((item, key) => {
        const found = item.filter((el) => el.a === curr.a && el.b === curr.b);
        if (found.length > 0) return memo[key].push(curr);
        else return memo.push([curr]);
      });

      return memo;
    },
    [[]]
  );

The needed result I try to get is

 [
    [
      { a: 1, b: 5 },
      { a: 1, b: 5 }
    ],
    [
      { a: 1, b: 6 },
      { a: 1, b: 6 },
    ],
    [
      { a: 1, b: 4 },
    ]
 ];

But as you can see if you try, because I push on the memo, the loop continue to fire. And the result contain hundreds arrays.

How I'm supposed to do to limit this loop and get the right result ?

Thanks a lot in advance :)

CodePudding user response：

You could use Map to group the element by the key of {a, b}, and then get the values of the group

const array = [
  { a: 1, b: 6 },
  { a: 1, b: 5 },
  { a: 1, b: 6 },
  { a: 1, b: 4 },
  { a: 1, b: 5 },
];

var newArray = Array.from(
  array
    .reduce((map, curr) => {
      const key = JSON.stringify({ a: curr.a, b: curr.b });

      if (!map.has(key)) {
        map.set(key, []);
      }

      map.get(key).push(curr);

      return map;
    }, new Map())
    .values()
);

console.log(newArray);

CodePudding user response：

Look at your code. You have a triple nested loop, which is insane and definitely not needed to achieve this. Why not use a map?

Here is a function that will do what you want to do with any array of objects given.

const array = [
    { a: 1, b: 6 },
    { a: 1, b: 5 },
    { a: 1, b: 6 },
    { a: 1, b: 4 },
    { a: 1, b: 5 },
];

const separate = (arr) => {
    const reduced = arr.reduce((acc, curr) => {
        const path = JSON.stringify(curr);

        if (!acc[path]) acc[path] = [];

        acc[path].push(curr);

        return acc;
    }, {});

    return Object.values(reduced);
};

console.log(separate(array));

CodePudding user response：

If you push inside for loop it will going to push for every reduce function iteration also.

you can achieve by adding some local variables like here

const array = [
    { a: 1, b: 6 },
    { a: 1, b: 5 },
    { a: 1, b: 6 },
    { a: 1, b: 4 },
    { a: 1, b: 5 }
  ];
  
  // shift changes the orginal array
    // it will remove and return firstElement
  var firstElement = array.shift(1);


  var newArray = array.reduce(
    (memo, curr) => {
    let isFound = false;
    let index = 0;
      memo.forEach((item, key) => {
        const found = item.filter((el) => el.a === curr.a && el.b === curr.b);
        if(found.length > 0){
             index = key;
           isFound = true;
           return;
        }
       
      });
      if(isFound) {
        memo[index].push(curr);
      } else {
         memo.push([curr]);
      }
      return memo;
    },
    [[firstElement]]
  );
  
  console.log(newArray);