Create a Map of Objects from an Array via Lodash

Question

I have the following array of arrays consisting of a name , age , and department

[[ "Kevin", 22,"Psychology" ],
[ "Cathy", 26, "Psychology" ],
[ "David", 31, "Engineering" ],
[ "Christine", 23, "Engineering" ]]

I want to create a map based on the unique departments that would look like this:

{ Psychology: [ 
  { name: "Cathy", age: 26 }, 
  { name: "Kevin", age: 22 } ] 
},
{ Engineering: [ 
  { name: "Christine", age: 23 }, 
  { name: "David", age: 31 } ] 
}

The index of department in the array will always be same. How can this be done utilizing lodash ?

Answer 1

Without using a external library, using new ESNext stuff like this is pretty easy.

 const data = [ [ "Kevin", 22,"Psychology" ], [ "Cathy", 26, "Psychology" ], [ "David", 31, "Engineering" ], [ "Christine", 23, "Engineering" ]]; const result = data.reduce((a, v) => { const [name,age,dept] = v; (a[dept] = a[dept] || []).push({name,age}); return a; }, {}); console.log(result); 

Answer 2

Here is a lodash solution:

 const {flow, groupBy, nth, mapValues, map, zipObject} = _ const transform = flow( people => groupBy(people, p => nth(p, 2)), grouped => mapValues(grouped, dept => map( dept, person => zipObject(['name', 'age'], person) )) ) const people = [["Kevin", 22, "Psychology"], ["Cathy", 26, "Psychology"], ["David", 31, "Engineering"], ["Christine", 23, "Engineering"]] console.log(transform(people)) 

 <script src="//cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.5/lodash.min.js"></script> 

It would probably be made simpler with lodash/fp, but I've never gotten that working correctly. I probably haven't spent much time on it because I'm one of the authors of another FP library for JS, Ramda . The solution above was created by translating my first code, written with Ramda:

 const {pipe, groupBy, nth, map, zipObj} = R; const transform = pipe( groupBy(nth(2)), map(map(zipObj(['name', 'age']))) ) const people = [["Kevin", 22, "Psychology"], ["Cathy", 26, "Psychology"], ["David", 31, "Engineering"], ["Christine", 23, "Engineering"]] console.log(transform(people)) 

 <script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script> 

I'm guessing that lodash/fp code would probably look pretty similar, except that you'd have to replace the first map with mapValues .