CODEWITHSUNDEEP
javascriptarrays
shobokshy
shobokshy

Reputation: 35

Splitting an array based on it's first value

hopefully you understand my question. Lets say I have this array:

[[1, 0.3], [1, 0.5], [2, 0.6], [2, 0.7], [3, 0.8], [3, 0.9]]

I want new arrays based on the first value like this:

[0.3, 0.5]
[0.6, 0.7]
[0.8, 0.9]

They are three arrays because there are three numbers 1 and 2 and 3. If there are more numbers, then more arrays should come out.

Thanks a lot.

Upvotes: 1

Views: 159

Answers (6)

Nina Scholz
Nina Scholz

Reputation: 386634

Just use Array.prototype.reduce() with a value for comparing the group.

var data = [[1, 0.3], [1, 0.5], [2, 0.6], [2, 0.7], [3, 0.8], [3, 0.9]],
    array = [];

data.reduce(function (r, a) {
    if (r === a[0]) {
        array[array.length - 1].push(a[1]);
    } else {
        array.push([a[1]]);
    }
    return a[0];
}, null);

document.write('<pre>' + JSON.stringify(array, 0, 4) + '</pre>');

Upvotes: 0

Dong Nguyen
Dong Nguyen

Reputation: 1269

If the first element is always non-negative number, something like this also works for you:

function merge(arr){
  var tmp = [];
  arr.map(function(item){
    var key = item[0], value = item[1];
    if(!tmp[key]){
      tmp[key] = [value];
    }
    else{
      tmp[key].push(value);
    }
  });

  return tmp.filter(function(item){
    return item ? true : false;
  });
}

http://jsfiddle.net/ndaidong/f1g882gy/

Input: [[1, 0.3], [1, 0.5], [2, 0.6], [2, 0.7], [3, 0.8], [3, 0.9]];

Output: [ [ 0.3, 0.5 ], [ 0.6, 0.7 ], [ 0.8, 0.9 ] ]

Input: [[1, 0.3], [4, 0.6], [3, 0.8], [4, 0.2], [1, 0.5], [2, 0.7], [2, 0.6], [3, 0.9]];

Output: [ [ 0.3, 0.5 ], [ 0.7, 0.6 ], [ 0.8, 0.9 ], [ 0.6, 0.2 ] ]

Upvotes: 0

sunzhida
sunzhida

Reputation: 35

Check for this:

var target = [[1, 0.3], [1, 0.5], [2, 0.6], [2, 0.7], [3, 0.8], [3, 0.9]];
var result = [];
for (var count=0; count<target.length; count++){
  var arrayCount = [];
  for (var elem in target) {
    if (target[elem][0] === count) {
        arrayCount.push(target[elem][1]);
    }
  }
  if (arrayCount.length !== 0) {
    result.push(arrayCount);
  }
}
//This is the result, i.e.: [[0.3, 0.5], [0.6, 0.7], [0.8, 0.9]]
console.log(result);

Upvotes: 0

Andy
Andy

Reputation: 63524

I agree with the other answerers that an object containing a set of arrays with keys corresponding to the number you want to group by is the way to go. Here's a solution using reduce. It passes in an empty object as an initial value.

var obj = arr.reduce(function (p, c) {

  // for each of the nested arrays we iterate over
  // set the key as the "groupBy" number
  // (the first element)
  var key = c[0];

  // if that key doesn't exist in the object (p)
  // that we've passed in
  // create it and assign a new array to it
  p[key] = p[key] || [];

  // push the second element of the array to the
  // array in the object
  p[key].push(c[1]);

  // pass the object in to the next iteration
  // of the reduce callback
  return p;

}, {});

DEMO

Output

{
  "1": [ 0.3, 0.5 ],
  "2": [ 0.6, 0.7 ],
  "3": [ 0.8, 0.9 ]
}

You can then get the data using square-bracket notation.

obj['1'][0] // 0.3

Upvotes: 0

Amir Popovich
Amir Popovich

Reputation: 29836

You can create a new object where the key will be the index number(first index of each current array value) and the value will be the relevant numbers (the second index).

var arr = [[1, 0.3], [1, 0.5], [2, 0.6], [2, 0.7], [3, 0.8], [3, 0.9]];

var newObj = {};

arr.map(function(item){
	if(newObj[item[0]])
  	   newObj[item[0]].push(item[1]);
        else
  	   newObj[item[0]] = [item[1]];
});

console.log('New object: ' + JSON.stringify(newObj));

// if you insist on creating an array

var newArr = [];
var cnt = 0;
for(var item in newObj)
{
   if(newObj.hasOwnProperty(item))
   {
      newArr[cnt] = newObj[item];
      cnt++;
   }
}

console.log('New array: ' + JSON.stringify(newArr));

Upvotes: 3

gurvinder372
gurvinder372

Reputation: 68393

check this fiddle

var arr = [[1, 0.3], [1, 0.5], [2, 0.6], [2, 0.7], [3, 0.8], [3, 0.9]];
var outputObj = {};
var outputArr = [];
for ( var counter = 0; counter < arr.length; counter++ )
{
   if ( !outputObj[ arr[ counter ][ 0 ] ] )
   {
      outputObj[ arr[ counter ][ 0 ] ] = [];
   }
   outputObj[ arr[ counter ][ 0 ] ].push( arr[ counter ][ 1 ] );
}
for( var id in outputObj )
{
   outputArr.push( outputObj[ id ] );
}
console.log( outputArr );

Upvotes: 0

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