Iterating through an array of objects and creating a new object with the iterate values

Question

First time posting on here and was hoping to get some help I can't seem to figure out how to do this problem. It's basically to create a function that receives an array of objects that returns a new object.

For some reason, push won't go through and returns the error property of push is undefined.

const organizeInstructors = function(instructors) {

  let output = {}; // so the obvious which is to create the object
  for (let i = 0; i < instructors.length; i++) {
    if (!output[instructors[course]]) {
      output[instructors[course]] = instructors[course];
    } else {
      output[instructors[course]].push(instructors[name]);
    }
  }
  return output;
};

console.log(organizeInstructors([{
    name: "Samuel",
    course: "iOS"
  },
  {
    name: "Victoria",
    course: "Web"
  },
  {
    name: "Karim",
    course: "Web"
  },
  {
    name: "Donald",
    course: "Web"
  }
]));

expected output

{
  iOS: ["Samuel"],
  Web: ["Victoria", "Karim", "Donald"]
}

Thanks for any advice or hints you guys can give

I think they were trying to do code formatting and add a couple of extra back ticks — Ameer
– Ameer, Commented Aug 14, 2020 at 0:37
You need to learn the difference between instructors[course] and instructors.course — Barmar
– Barmar, Commented Aug 14, 2020 at 0:51

MarkCBall · Accepted Answer · 2020-08-14 00:43:52Z

2

Looks like you were getting a bit confused iterating over arrays vs keying into objects.

let organizeInstructors = function(instructors) {
let output = {}; // so the obvious which is to create the object
  for(let i = 0; i < instructors.length; i++) { 
    const instructor = instructors[i]
    if(!output[instructor.course]) { 
      output[instructor.course] = []
    }                                                   
    output[instructor.course].push(instructor.name)   
   }
return output;
}
console.log(organizeInstructors([
  {name: "Samuel", course: "iOS"},
  {name: "Victoria", course: "Web"},
  {name: "Karim", course: "Web"},
  {name: "Donald", course: "Web"}
]))

Adding the const instructor makes it much easier to read as well

edited Aug 14, 2020 at 0:43

answered Aug 14, 2020 at 0:37

MarkCBall

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1 Comment

Despot Over a year ago

Hi MarkCBall, Thank you so much!

Jhecht · Accepted Answer · 2020-08-14 00:44:30Z

This uses the Array.prototype.reduce method.

Please note that this will not check if the value is already present in the course array and will just blindly add in. This could mean that you get multiple instances of the same name in the same course.

const organizeInstructors = function(instructors) {
  return instructors.reduce((cumulative, current) => {
    // if we don't have a course in cumulative object, add it.
    if (!cumulative[current.course]) cumulative[current.course] = [];
    // add in the current name.
    cumulative[current.course].push(current.name);
    // return the cumulative object for the next iteration.
    return cumulative;
  }, {});
}
console.log(organizeInstructors([{
    name: "Samuel",
    course: "iOS"
  },
  {
    name: "Victoria",
    course: "Web"
  },
  {
    name: "Karim",
    course: "Web"
  },
  {
    name: "Donald",
    course: "Web"
  }
]));

Sven.hig · Accepted Answer · 2020-08-19 06:11:20Z

0

Using reduce

data = [ { name: "Samuel", course: "iOS" }, { name: "Victoria", course: "Web" }, { name: "Karim", course: "Web" }, { name: "Donald", course: "Web" }, ];
getObj = (data) =>
  data.reduce(
    (r, c) => (
      !r[c.course] // checks if accumulator doesn't have c.course as key  
        ? ((r[c.course] = []), r[c.course].push(c.name)) // then make an array that corresponds the key then push c.name
        : r[c.course].push(c.name), // else push c.name to the corresponding array 
      r
    ),
    {}
  );
console.log(getObj(data));

edited Aug 19, 2020 at 6:11

answered Aug 14, 2020 at 0:43

Sven.hig

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1 Comment

Jhecht Over a year ago

you may want to explain the first part of your ternary --

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