java script 2D array find unique array combinations

Question

I need to know the best way to get following results

courseFrequency : [
{
      'courses': [
        'a.i'
      ],
      'count' : 1
},
{
      'courses': [
        'robotics'
      ],
      'count' : 2

},
{
      'courses': [
        'software engineering', 'a.i'
      ],
      'count' : 2         
},
    {
      'courses': [
        'software engineering', 'a.i','robotics'
      ],
      'count' : 1
}

]

from following json data.

arr = [
    {
      'courses': [
        'a.i'
      ]
    },
    {
      'courses': [
        'robotics'
      ]
    },
    {
      'courses': [
        'software engineering', 'a.i'
      ]
    },
    {
      'courses': [
        'robotics'
      ]
    },
    {
      'courses': [
        'software engineering', 'a.i'
      ],

      'courses': [
        'software engineering', 'a.i','robotics'
      ]       

    }];

Basically i need to find out the unique courses and their frequency. What is the most optimal way to do that ?

I'm voting to close this question as off-topic because the question does not show any sign of effort. this is a requirement and not a problem statement. — Rajesh Dixit
– Rajesh Dixit, Commented Dec 1, 2017 at 6:05

Jonas Wilms · Accepted Answer · 2017-12-01 06:22:30Z

3

const hash = {}, result = [];

for(const {courses} of arr){
  const k = courses.join("$");
  if(hash[k]){
    hash[k].count++;
  } else {
    result.push(hash[k] = { courses, count : 1 });
  }
}

Simply use a hashmap to find duplicates. As arrays are compared by reference, we need to join it to a string for referencing ( note that this will fail if a coursename contains the joining symbol ($))

answered Dec 1, 2017 at 6:22

Jonas Wilms

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5 Comments

Rajesh Dixit Over a year ago

should we not expect OP to share effort? In my POV, answering such questions will promote spoon feeding.

Jonas Wilms Over a year ago

@rajesh i think it depends on the difficulty of the question. I admit that this case is debateable, however im friendly today ;)

Rajesh Dixit Over a year ago

That doesn't sound right! Discipline should not depend on mood, but this is an opinionated comment and I hope someone other than me feels the same. Have a good day :-)

Jonas Wilms Over a year ago

@rajesh if we close all noob questions, there would be no one explaining things to them so they will land on pages like w3schools etc. No one wants that. And this question would be really good if the op would add its tries.

Rajesh Dixit Over a year ago

Can't agree more in relation to w3schools. Point taken.

A.D. · Accepted Answer · 2017-12-01 06:07:47Z

There both of them are best for area relates to them.These concepts are heaving their own property and methods to accomplish a certain task like JSON used for data transfer and cross browsing aspect as the common type data value.Arrays are really good at storing ordered lists and ordering things while the cost of removing/splicing elements is a bit higher.

JSON is a representation of the data structure, it's not an object or an array. JSON can be used to send data from the server to the browser, for example, because it is easy for JavaScript to parse into a normal JavaScript data structure.for doing an action on JSON data you need to convert it into an object which is also seamed some property like ARRAY. Arrays are really good at storing ordered lists and ordering things while the cost of removing/splicing elements is a bit higher.

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