Create 2 Dimensional Array from Object with same key

Pat Doyle :

I have an array of objects that I want to transform. My dataset looks like this:

[
 {
  day: sunday,
  val: 20
 }, 
{
  day: sunday,
  val: 20
 }, 
{
  day: monday,
  val: 10
 },  
{
  day: monday,
  val: 30
 }, 
{
  day: tuesday,
  val: 5
 }, 
{
  day: tuesday,
  val: 5
 }
]

I am trying to transform the data to look like this:

Output: [[20,20], [10,30], [5, 5]]

Where each of the nested arrays are based on the Day of Week in object. Any ideas?

Thanks!

Mr. Polywhirl :

You could group your items by their day. After you have the groups, you can grab the values of the map and map the item lists to a list of val.

const data = [
  { day: 'sunday'  , val: 20 }, { day: 'sunday'  , val: 20 },
  { day: 'monday'  , val: 10 }, { day: 'monday'  , val: 30 },
  { day: 'tuesday' , val:  5 }, { day: 'tuesday' , val:  5 }
];

const transformed = Object.values(data.reduce((map, item) =>
  ({ ...map, [item.day] : [ ...(map[item.day] || []), item]
}), {})).map(list => list.map(item => item.val));

console.log(transformed);

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

Alternatively, you can reduce the values right away, but you lose all the item properties.

const data = [
  { day: 'sunday'  , val: 20 }, { day: 'sunday'  , val: 20 },
  { day: 'monday'  , val: 10 }, { day: 'monday'  , val: 30 },
  { day: 'tuesday' , val:  5 }, { day: 'tuesday' , val:  5 }
];

const transformed = Object.values(data.reduce((map, item) =>
  ({ ...map, [item.day] : [ ...(map[item.day] || []), item.val] }), {}));

console.log(transformed);

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

Here is a functional version:

const data = [
  { day: 'sunday'  , val: 20 }, { day: 'sunday'  , val: 20 },
  { day: 'monday'  , val: 10 }, { day: 'monday'  , val: 30 },
  { day: 'tuesday' , val:  5 }, { day: 'tuesday' , val:  5 }
];

const toMatrix = (list, key, valFn) => Object.values(data.reduce((map, item) =>
  ({ ...map, [item[key]] : [ ...(map[item[key]] || []), valFn(item) ] }), {}))

console.log(toMatrix(data, 'day', item => item.val));

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

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edited at2020-09-15

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Create 2 Dimensional Array from Object with same key

Create 2 Dimensional Array from Object with same key

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