Manipulation of array in angularjs/javascript

Question

I have the following array:

 [["1", "2", "Anna"], ["1", "2", "Jodie"], ["1", "2", "susan"]]

My question is how can I output them as shown below?

I want to get all 1 as there parent index:

(
 [1] =>Array
      (
      [2] => 3
      )
)

The number 1 means the O index of array of arrays.

The 2 is the 1 index and 3 means how many students which 1 index is equal to two. In above array there are 3 students.

Any ideas?

Answer 1

My understanding is that, given a record in the form [a, b, c], You want to produce an array summing the number of times you can reach a value by traversing through a to b.

Given [ [a,b,x], [a,b,y], [a,b,z] ] your output would be{a: {b: 3}}.

Given [ [a,b,x], [a,b,y], [c,d,x], [c,d,y], [e,f,z]], your output would be

{
  a: {
    b: 2
  },
  c: {
    d: 2
  },
  e: {
    f: 1
  }
}

This is relatively simple:

    records = [
      ["1", "2", "Anna"],
      ["1", "2", "Jodie"],
      ["1", "2", "susan"]
    ]
   
    data = {}; // this will hold your final structure
    
    records.forEach(function (r) {
      var first = r[0], second = r[1];

      // create the first dimension unless it exists
      data[first] || (data[first] = {});
    
      // create the second dimension unless it exists
      data[first][second] || (data[first][second] = 0); 
    
      data[first][second]++;
    });
    
    console.log(data);  // { "1": { "2": 3 } }