Filtering one object with another array's object key

Question

I am trying to filter an object with another object inside of an array.

To be more precise, I am trying to compare the keys of the object inside the array, to the keys of my main object. If the values are the same, I want to return the value corresponding to those keys.

Here's an example:

var a = {
  "maths":"A++",
  "literature":"C-",
  "sports":"B+",
  "biology":"D",
  "chemistry":"A",
  "english":"A+",
  "physics":"C+"
}


var b = [{
  "maths":"Mathematics",
  "biology":"Biology",
  "physics":"Physics"
}]

I wanna check if any of the keys in object b are inside object a and if they are, I want to return their value into array. For example, I want to return ["A++","D","C+"]

I've tried using filter and Array.prototype.some but I couldn't figure out anything. Any advice on how should I achieve this?

Answer 1

First make an array or Set of all the keys inside b , then use .map to access each key on the a object:

 var a = { "maths":"A++", "literature":"C-", "sports":"B+", "biology":"D", "chemistry":"A", "english":"A+", "physics":"C+" } var b = [{ "maths":"Mathematics", "biology":"Biology", "physics":"Physics" }]; const keys = b.flatMap(Object.keys); const arr = keys.map(key => a[key]); console.log(arr);

Answer 2

If you are dealing with a single object in the array b , then you can do this:

 var a = { "maths":"A++", "literature":"C-", "sports":"B+", "biology":"D", "chemistry":"A", "english":"A+", "physics":"C+" } var b = [{ "maths":"Mathematics", "biology":"Biology", "physics":"Physics" }] const valuesInAndB = Object.keys(a).reduce((acc,x) => { if (b[0][x]) { return acc.concat(a[x]); } return acc; }, []); console.log(valuesInAndB);

However, if the objects in b will be greater than one then as answered by @certainperformance you could get all the keys in b and map through a with those keys.

const keysInB = b.flatMap(Object.keys);
keysInB.map(key => a[key]);

flatMap is not available in some older browsers, please keep that in mind.

Answer 3

I'm assuming that you want to handle multiple objects in b. If so and if you want one array for each object in b then you could do something like:

 var a = { "maths":"A++", "literature":"C-", "sports":"B+", "biology":"D", "chemistry":"A", "english":"A+", "physics":"C+" } var b = [{ "maths":"Mathematics", "biology":"Biology", "physics":"Physics" },{ "maths":"Mathematics", "biology":"Biology", "english":"English" }] const result = b.map(obj => Object.keys(obj).map(key => a[key])); console.log(result);