create an array from keys of another array which has values

Question

I have an object / associate array which has name and values. I am trying to create another array based on the keys of the array which has values.

This is the array

0: {country: "AFG", Biomass: null, Coal: null, Cogeneration: null, Gas: 42}  
1: {country: "AGO", Biomass: 10, Coal: 20, Cogeneration: null, Gas: null}

new array should skip the first element and start with next element and generate an array from keys which has values. result array

{"Biomass","Gas","Coal"}

Biomass, Coal and Gas has values therefore should appear in the new array. country is the first element and shouldn't appear. I tried google, but couldn't help.

var ks = Object.keys(output);
console.log(ks);

this return only 0 and 1

Why would skip the first element? there is a key named Gas that have a value on the first object. Also, do you want an array of not null key for every object on the original array or only one array for the complete original array that collect all the keys that are not null in some of the objects? — Shidersz
– Shidersz, Commented Feb 15, 2019 at 2:43

Code Maniac · Accepted Answer · 2019-02-15 04:41:00Z

3

You can use reduce and Set

let arr = [ {country: "AFG", Biomass: null, Coal: null, Cogeneration: null, Gas: 42},{country: "AGO", Biomass: 10, Coal: 20, Cogeneration: null, Gas: null}]

let op = arr.reduce((op,inp)=>{
  Object.keys(inp).forEach((e,index)=>{
    if(!op.has(inp[e]) && index !== 0 && inp[e]){
      op.add(e)
    }
  })
  return op;
},new Set())

console.log([...op])

edited Feb 15, 2019 at 4:41

answered Feb 15, 2019 at 2:33

Code Maniac

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1 Comment

Tyler Roper Over a year ago

Based on OP's described output and this quote: "Biomass, Coal and Gas has values therefore should appear in the new array." - it sounds like Cogeneration shouldn't be included as neither record has a value for it.

Gabor Szekely · Accepted Answer · 2019-02-15 02:49:46Z

2

Object.keys as applied to the main array would only be referring to the 'keys' of the array, i.e. the zero-based index of the objects, which is why you are getting 0 and 1.

If you want to get the keys of the objects contained within the array, you should do something like this:

let energySources = array.reduce((acc, item) => {
  for (let key in item) {
    if (item[key] !== null && key !== "country") {
      acc.push(key);
    }
  }
  return acc;
}, []);

let uniqueValues = [...new Set(energySources)];

edited Feb 15, 2019 at 2:49

answered Feb 15, 2019 at 2:35

Gabor Szekely

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5 Comments

ARH Over a year ago

Thanks, this gives me the result, but it shows duplicate keys

Gabor Szekely Over a year ago

That's why you have to run this line: let uniqueValues = [...new Set(energySources)];

ARH Over a year ago

It print "Gas" twice.

Gabor Szekely Over a year ago

You can do this: let uniqueValues = energySources.reduce((acc,item) => acc.includes(item) ? acc : [...acc, item], [])

ARH Over a year ago

My mistake, It was perfectly working. Thanks a lot and appreciate it.

random · Accepted Answer · 2019-02-15 02:59:49Z

0

const input = [
  {country: "AFG", Biomass: null, Coal: null, Cogeneration: null, Gas: 42} ,
  {country: "AGO", Biomass: 10, Coal: 20, Cogeneration: null, Gas: null}
];

const output = input.reduce((accu, {country, ...rest}) => {
  Object.keys(rest).forEach((key) => {
    if(rest[key] && !accu.includes(key)) {
      accu.push(key);
    }
  });
  return accu;
}, []);

console.log(output);

answered Feb 15, 2019 at 2:59

random

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Comments

Shidersz · Accepted Answer · 2019-02-15 03:00:41Z

0

Here you have another approach with reduce() that will generate an object with true values for a key that has a value. Finally, we generate you array using Object.keys() on it.

const input = [
  {country: "AFG", Biomass: null, Coal: null, Cogeneration: null, Gas: 42},
  {country: "AGO", Biomass: 10, Coal: 20, Cogeneration: null, Gas: null}
];

let res = input.reduce((acc, curr) =>
{
    Object.keys(curr).forEach(
        (k, i) => !acc[k] && i > 0 && curr[k] && (acc[k] = true)
    );
    return acc;
}, {});

res = Object.keys(res);
console.log(res);

answered Feb 15, 2019 at 3:00

Shidersz

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Comments

sagar1025 · Accepted Answer · 2019-02-15 03:01:03Z

0

var objArr = [
{country: "AFG", Biomass: null, Coal: null, Cogeneration: null, Gas: 42} ,
 {country: "AGO", Biomass: 10, Coal: 20, Cogeneration: null, Gas: null}
]

var result = [];

function filterArr(item) {
	for(var j in item) {
  	if(j !== 'country') {
    	if(item[j]) {
      	result.push(j);
      }
    }
  }
}

for(var i of objArr) {
filterArr(i);
}

for(var p of result) {
	console.log(p);
}

answered Feb 15, 2019 at 3:01

sagar1025

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Comments

Tyler Roper · Accepted Answer · 2019-02-15 04:36:12Z

0

Iterate through the array with arr.reduce().
With each iteration, get the object's keys using getOwnPropertyTypes().
filter() out any keys whose value is null, key is country, or key is already included in our output.

const arr = [ {country: "AFG", Biomass: null, Coal: null, Cogeneration: null, Gas: 42},{country: "AGO", Biomass: 10, Coal: 20, Cogeneration: null, Gas: null}];

let result = arr.reduce((output, i) => [
  ...output, 
  ...Object.getOwnPropertyNames(i)
      .filter(k => i[k] && k !== "country" && !output.includes(k))
  ], []);

console.log(result);

While iterating, we add the current results to our output using spread syntax. E.g., [...arr1, ...arr2] would combine the contents of arr1 and arr2.

edited Feb 15, 2019 at 4:36

answered Feb 15, 2019 at 3:12

Tyler Roper

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Comments

user3153210 · Accepted Answer · 2021-05-24 12:41:57Z

-2

Is this what you mean or did I missunderstand?

array1.forEach(function(item,index){ array2[item] = index;});

answered May 24, 2021 at 12:41

user3153210

1

1 Comment

tantalum Over a year ago

This does not answer the original question and would be better as a comment.

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