How to replace object A to B in an arrays if the object A got same property in object B

Question

I'm trying to get an array from two different arrays. I'm not sure how to do it with ES6.

I want the current_year_data is replacing to previous_year_data

The First array is:

let previous_year_data = [
  { month: "January", value: 300 },
  { month: "February", value: 1 },
  { month: "March", value: 2 },
  { month: "April", value: 3 },
  { month: "May", value: 4 },
  { month: "Jun", value: 5 },
  { month: "July", value: 6 },
  { month: "August", value: 7 },
  { month: "September", value: 8 },
  { month: "October", value: 9 },
  { month: "November", value: 10 },
  { month: "December", value: 11 },
];

Second array:

let current_year_data = [
  { month: "January", value: 4459 }
];

The result should be in:

let current_year_data = [
  { month: "January", value: 4459 },
  { month: "February", value: 1 },
  { month: "March", value: 2 },
  { month: "April", value: 3 },
  { month: "May", value: 4 },
  { month: "Jun", value: 5 },
  { month: "July", value: 6 },
  { month: "August", value: 7 },
  { month: "September", value: 8 },
  { month: "October", value: 9 },
  { month: "November", value: 10 },
  { month: "December", value: 11 },
];

Thanks

score 0 · Answer 1 · answered Jan 20 '20 at 09:53

It is possible to use map method. In addition, you can use Map collection to have O(1) of access to elements items when you map your array:

let unique = new Map(current_year_data.map(s=> [s.month, s.value]))
previous_year_data.map(({month, value})=> ({month, value: unique.get(month) || value }));

An example:

let previous_year_data = [
  { month: "January", value: 300 },
  { month: "February", value: 1 },
  { month: "March", value: 2 },
  { month: "April", value: 3 },
  { month: "May", value: 4 },
  { month: "Jun", value: 5 },
  { month: "July", value: 6 },
  { month: "August", value: 7 },
  { month: "September", value: 8 },
  { month: "October", value: 9 },
  { month: "November", value: 10 },
  { month: "December", value: 11 },
];

let current_year_data = [
  { month: "January", value: 4459 }
];

let unique = new Map(current_year_data.map(s=> [s.month, s.value]))
const result = previous_year_data.map(({month, value})=> 
    ({month, value: unique.get(month) || value }));
console.log(result)

Arun Saini · Answer 2 · 2020-01-21T10:34:44.590

For such requirements, combine or merge JSON arrays unique by the key will work! See the following:

// Note: this will pick the last duplicated item in the list.

const previous_year_data = [
  { month: "January", value: 300 },
  { month: "February", value: 1 },
  { month: "March", value: 2 },
  { month: "April", value: 3 },
  { month: "May", value: 4 },
  { month: "Jun", value: 5 },
  { month: "July", value: 6 },
  { month: "August", value: 7 },
  { month: "September", value: 8 },
  { month: "October", value: 9 },
  { month: "November", value: 10 },
  { month: "December", value: 11 },
];

const current_year_data = [
  { month: "January", value: 4459 }
];

const key = 'month'; //Replace this key with unique key

const result = [...new Map([...previous_year_data, ...current_year_data].map(item =>
  [item[key], item])).values()];
  
console.log(result);

/*OUTPUT

[
  {
    "month": "January",
    "value": 4459
  },
  {
    "month": "February",
    "value": 1
  },
  {
    "month": "March",
    "value": 2
  },
  {
    "month": "April",
    "value": 3
  },
  {
    "month": "May",
    "value": 4
  },
  {
    "month": "Jun",
    "value": 5
  },
  {
    "month": "July",
    "value": 6
  },
  {
    "month": "August",
    "value": 7
  },
  {
    "month": "September",
    "value": 8
  },
  {
    "month": "October",
    "value": 9
  },
  {
    "month": "November",
    "value": 10
  },
  {
    "month": "December",
    "value": 11
  }
]

*/

How to replace object A to B in an arrays if the object A got same property in object B

2 Answers2