Need to mapped data between two arrays

Question

Need some help to solve basic task.

I have two arrays of objects.

const firstArr = [
  {id: 1, action: 'pending'},
  {id: 2, action: 'pending'},
  {id: 3, action: 'pending'},
];

const secondArr = [
  {id: 1, action: 'accepted'},
  {id: 2, action: 'accepted'},
  {id: 3, action: 'accepted'},
  {id: 566, action: 'accepted'},
  {id: 333, action: 'accepted'},
  {id: 234, action: 'accepted'},
];

I need to find in second array all objects with equal ids from first array and change "action" property in second array on "action" property from first array

What have you tried? There are many similar questions on SO. Please see stackoverflow.com/help/how-to-ask. — isherwood
– isherwood, Commented Jan 15, 2021 at 17:37
Does this answer your question? How to merge multiple array of object by ID in javascript? — mohammad javad ahmadi
– mohammad javad ahmadi, Commented Jan 15, 2021 at 17:42

phi-rakib · Accepted Answer · 2021-01-15 17:58:58Z

1

You could use Map Object. Traverse the first array and set id as key and action as a value into Map Object. Then traverse the second array and look for id in the Map Object. If id is found then change the action.

const firstArr = [
  { id: 1, action: 'pending' },
  { id: 2, action: 'pending' },
  { id: 3, action: 'pending' },
];

const secondArr = [
  { id: 1, action: 'accepted' },
  { id: 2, action: 'accepted' },
  { id: 3, action: 'accepted' },
  { id: 566, action: 'accepted' },
  { id: 333, action: 'accepted' },
  { id: 234, action: 'accepted' },
];
const map = new Map();
firstArr.forEach(({ id, action }) => map.set(id, action));
const ret = secondArr.map((x) =>
  map.has(x.id) ? { ...x, action: map.get(x.id) } : { ...x }
);
console.log(ret);

edited Jan 15, 2021 at 17:58

answered Jan 15, 2021 at 17:50

phi-rakib

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1 Comment

P.S. Over a year ago

This implementation looks elegant

codemonkey · Accepted Answer · 2021-01-15 17:40:13Z

Here is one way to do that

const firstArr = [
  {id: 1, action: 'pending'},
  {id: 2, action: 'pending'},
  {id: 3, action: 'pending'},
];

const secondArr = [
  {id: 1, action: 'accepted'},
  {id: 2, action: 'accepted'},
  {id: 3, action: 'accepted'},
  {id: 566, action: 'accepted'},
  {id: 333, action: 'accepted'},
  {id: 234, action: 'accepted'},
];

secondArr.forEach((item, index) => {
  const fa = firstArr.find(i => i.id === item.id);
  if(fa)
    secondArr[index].action = fa.action
})
console.log(secondArr)

Loop through the second array, try to find a corresponding element in the first array and then, if found, grab its action and assign to to the proper index of the second array. Pretty basic, as you pointed out.

Nina Scholz · Accepted Answer · 2021-01-15 17:46:00Z

0

You could gather all actions and map a new object with the wanted values.

const
    firstArr = [{ id: 1, action: 'pending' }, { id: 2, action: 'pending' }, { id: 3, action: 'pending' }],
    secondArr = [{ id: 1, action: 'accepted' }, { id: 2, action: 'accepted' }, { id: 3, action: 'accepted' }, { id: 566, action: 'accepted' }, { id: 333, action: 'accepted' }, { id: 234, action: 'accepted' }],
    states = Object.fromEntries(firstArr.map(({ id, action }) => [id, { action }])),
    result = secondArr.map(o => ({ ...o, ...states[o.id] }));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Jan 15, 2021 at 17:46

Nina Scholz

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