This previous question es closest to what I am curious of. I've tried several variations of indexOf() and filter() to no success

I have an arrays of objects (exampleDat):

[{id:1, value:"100", name:"dog", D1: 10, D2: 67, D3: 33},
{id:2, value:"200", name:"cat", D1: 66, D2: 41, D3: 34},
{id:3, value:"300", name:"fish", D1: 23, D2: 45, D3:},
{id:4, value:"400", name:"mouse", D1: 13, D2: 55, D3:},
{id:5, value:"500", name:"snake", D1: 7, D2: 9, D3:}]

In a different function, I return an array of which of these 'keys' I need. This array changes dynamically, so its not possible to type them all out. For example any of the following examples are viable,

useThese1 = ['D1','D2'] //Want exampleDat returned with only these key,value 'columns' returned
useThese2 = ['id','D1','D2','D3'] //Want exampleDat return with only these key,value 'columns' returned
useThese3 = ['value','D2','D3'] //Want exampleDat returned with only these key,value 'columns' returned

So I need to dynamically map the values in a useThese array to the exampleDat array

If I knew the exact columns, I could hand type it ala:

exampleDat.map(d => {return {D1: d.D1, D2: d.D2}})

But I need something like:

dat.map(d => useThese1.map(g =>  {return {something?}}) ???

In R, it would simply and easily be exampleDat[,colnames(exampleDat) %in% useThese1]

This previous question es closest to what I am curious of. I've tried several variations of indexOf() and filter() to no success

I have an arrays of objects (exampleDat):

[{id:1, value:"100", name:"dog", D1: 10, D2: 67, D3: 33},
{id:2, value:"200", name:"cat", D1: 66, D2: 41, D3: 34},
{id:3, value:"300", name:"fish", D1: 23, D2: 45, D3:},
{id:4, value:"400", name:"mouse", D1: 13, D2: 55, D3:},
{id:5, value:"500", name:"snake", D1: 7, D2: 9, D3:}]

In a different function, I return an array of which of these 'keys' I need. This array changes dynamically, so its not possible to type them all out. For example any of the following examples are viable,

useThese1 = ['D1','D2'] //Want exampleDat returned with only these key,value 'columns' returned
useThese2 = ['id','D1','D2','D3'] //Want exampleDat return with only these key,value 'columns' returned
useThese3 = ['value','D2','D3'] //Want exampleDat returned with only these key,value 'columns' returned

So I need to dynamically map the values in a useThese array to the exampleDat array

If I knew the exact columns, I could hand type it ala:

exampleDat.map(d => {return {D1: d.D1, D2: d.D2}})

But I need something like:

dat.map(d => useThese1.map(g =>  {return {something?}}) ???

In R, it would simply and easily be exampleDat[,colnames(exampleDat) %in% useThese1]

• javascript
• arrays
• object

6 Answers 6

You could map the new keys.

const
    mapWith = (array, keys) => array.map(o => Object.fromEntries(keys.map(k => [k, o[k]]))),
    data = [{ id: 1, value: "100", name: "dog", D1: 10, D2: 67, D3: 33 }, { id: 2, value: "200", name: "cat", D1: 66, D2: 41, D3: 34 }, { id: 3, value: "300", name: "fish", D1: 23, D2: 45, D3:97}, { id: 4, value: "400", name: "mouse", D1: 13, D2: 55, D3:98}, { id: 5, value: "500", name: "snake", D1: 7, D2: 9, D3:99}],
    result1 = mapWith(data, ['D1', 'D2']),
    result2 = mapWith(data, ['id', 'D1', 'D2', 'D3']),
    result3 = mapWith(data, ['value', 'D2', 'D3']);

console.log(result1);
console.log(result2);
console.log(result3);

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

Object.fromEntries are relatively recent, but easily polyfilled.

Here is my solution. This uses the ES5 Javascript functions

const selectKeys = (keys, data) => {
    return data.map(item => keys.reduce((prev, key) => {
        prev[key] = item[key]
        return prev
    }, {}))
}

const selData1 = selectKeys(useThese1, data)
const selData2 = selectKeys(useThese2, data)
const selData3 = selectKeys(useThese3, data)

You can do something like this

const arr = [
  { id: 1, value: "100", name: "dog", D1: 10, D2: 67, D3: 33 },
  { id: 2, value: "200", name: "cat", D1: 66, D2: 41, D3: 34 },
  { id: 3, value: "300", name: "fish", D1: 23, D2: 45, D3: 34 },
  { id: 4, value: "400", name: "mouse", D1: 13, D2: 55, D3: 34 },
  { id: 5, value: "500", name: "snake", D1: 7, D2: 9, D3: 34 }
];

function dynamicFilter(data, requiredKeys) {
    return data.map((item) => {
        const result = {};
        requiredKeys.forEach(key => result[key] = item[key]);
        return result;
    });
}

console.log(dynamicFilter(arr, ['D1','D2']));
console.log(dynamicFilter(arr, ['id','D1','D2','D3']));

You can do something like this:

const arr = [{id:1, value:"100", name:"dog", D1: 10, D2: 67, D3: 33}, {id:2, value:"200", name:"cat", D1: 66, D2: 41, D3: 34}, {id:3, value:"300", name:"fish", D1: 23, D2: 45, D3:11}, {id:4, value:"400", name:"mouse", D1: 13, D2: 55, D3:11}, {id:5, value:"500", name:"snake", D1: 7, D2: 9, D3:11}];

const useThese1 = ['D1','D2'];
const useThese2 = ['id','D1','D2','D3'];
const useThese3 = ['value','D2','D3'];

const getResult = (keys) => arr.map(v => keys.reduce((a, c) => (a[c] = v[c], a), {}));

[useThese1, useThese2, useThese3].forEach(v => console.log(getResult(v)));

Here's an imperative way to do it. It could be shortened with ES6 array methods.

let exampleDat = [
  {id:1, value:"100", name:"dog", D1: 10, D2: 67, D3: 33},
  {id:2, value:"200", name:"cat", D1: 66, D2: 41, D3: 34},
  {id:3, value:"300", name:"fish", D1: 23, D2: 45, D3: 8},
  {id:4, value:"400", name:"mouse", D1: 13, D2: 55, D3: 8},
  {id:5, value:"500", name:"snake", D1: 7, D2: 9, D3: 8}
],
useThese1 = ['D1','D2']

function getColumns(data, useWhich){
  let result = [];
  for(let row of data){
    let keys = Object.keys(row);
    let filteredRow = {};
    for(let key of keys){
      if(useWhich.includes(key)){
        filteredRow[key] = row[key];
      }
    }
    result.push(filteredRow);  
  }
  return result;
}

console.log(getColumns(exampleDat, useThese1));

Here's a "for dummies" version of the accepted answer.
(The more verbose variable names helped me understand how the algorithm works.)

const
  selectColumns = (unfilteredData, colsToKeep) => 
    unfilteredData.map(row =>
      Object.fromEntries(colsToKeep.map( col => [col, row[col]] )
    )
  ),

  data = [
    { id: 1, value: "100", name: "dog", D1: 10, D2: 67, D3: 33 },
    { id: 2, value: "200", name: "cat", D1: 66, D2: 41, D3: 34 },
    { id: 3, value: "300", name: "fish", D1: 23, D2: 45, D3:97 },
    { id: 4, value: "400", name: "mouse", D1: 13, D2: 55, D3:98 },
    { id: 5, value: "500", name: "snake", D1: 7, D2: 9, D3:99 }
  ],

  colNames1 = ['D1', 'D2'],
  result1 = selectColumns(data, colNames1);
console.log(result1);