在 Javascript 的多维数组中合并具有相同日期的值

Question

I have one array which has two values one date and an amount but there is the same date with a different value at a different index so I need to merge those values into the same date in a multidimensional javascript array

current array

var arry = [
['2021-05-01',100], 
['2021-05-02',300], 
['2021-05-03',200], 
['2021-05-01',150],
['2021-05-02',300], 
['2021-05-01',600],
['2021-05-04',120]
]

Expected Result Array

var arry = [
['2021-05-01',850], 
['2021-05-02',600], 
['2021-05-03',200], 
['2021-05-04',120]]

Can anybody help? I really appreciate any help you can provide.

Answer 1

You can use reduce method:

 var arry = [ ['2021-05-01',100], ['2021-05-02',300], ['2021-05-03',200], ['2021-05-01',150], ['2021-05-02',300], ['2021-05-01',600], ['2021-05-04',120] ]; const data = arry.reduce((list, [date, value]) => { list[date] = (list[date]?? 0) + value; return list; }, {}); const list = Object.entries(data); // if you want the array console.log(list);

Answer 2

Here is a solution using reduce . I'm creating an object grouped by date and taking the values array of it

 var arry = [['2021-05-01',100], ['2021-05-02',300], ['2021-05-03',200], ['2021-05-01',150],['2021-05-02',300], ['2021-05-01',600],['2021-05-04',120]] const res = Object.values(arry.reduce((acc,[date,val])=> { acc[date] = acc[date] || [date,0] acc[date][1]+=val return acc },{})) console.log(res)

Answer 3

You could likely just loop through the list, and at each value in the list check all of the values that came before to see if it is a repeat. Something like the following would work:

var array = [
  ['2021-05-01',100], 
  ['2021-05-02',300], 
  ['2021-05-03',200], 
  ['2021-05-01',150],
  ['2021-05-02',300], 
  ['2021-05-01',600],
  ['2021-05-04',120]
]

var newArray = []; // where we will put the new merged values

for (var lookAtOldArray = 0; lookAtOldArray < array.length; lookAtOldArray++) {
  // check all previous values in newArray up to this point:
  var checkNewArray; // declare out here for logic post loop
  for (checkNewArray = 0; checkNewArray < newArray.length; checkNewArray++) {
    if (array[lookAtOldArray][0] == newArray[checkNewArray][0]) {
      // add to newArray number:
      newArray[checkNewArray][1] += array[lookAtOldArray][1];
      break; // BREAK to signify we found a position
    }

    // otherwise keep looking
  }

  // because of the break, if checkNewArray == newArray.length, then we DID NOT find a duplicate (AKA: push to newArray with exact value in array)
  if (checkNewArray == newArray.length) {
     newArray.push(array[lookAtOldArray]);
  }
}

another interesting idea would be to use objects. The above strategy would require looking the data more times than necessary (n^2 for worst cases). With an object, you could use the date as a key, and the number as the value. With that, you could do something like this (assuming the same declaration of array :

var combinedDates = {};

for (var lookAtOldArray = 0; lookAtOldArray < array.length; lookAtOldArray++) {
  combinedDates[array[lookAtOldArray][0]] += array[lookAtOldArray[1];
}

You can tell this is a lot faster and simpler. The resulting object would look like this:

{
  "2021-05-01": 850,
  "2021-05-02": 600,
  "2021-05-03": 200,
  "2021-05-04": 120
}

I'm preferential to the second one because of the efficiency increase; you only ever have to look at each element in the initial array once (resulting in n , or linear, time complexity)!

If you want to combine the above object back into an array, you could then do:

// get object keys
var objectKeys = Object.keys(combinedDates);
var newArray = [];

// loop through keys
for (var makeObject = 0; makeObject < objectKeys.length; makeObject++) {
  // create array with key (the date) and the number (the value stored at the key):
  newArray.push([objectKeys[makeObject][0], combinedDates[objectKeys[makeObject]]);
}