reduce array to a by grouping objects with same property

Question

I have an array of objects and I am trying to group them by similar property value. So lets say here is array

[  
  {  
    \"size\":\"6.5\",
    \"width\":\         


        

Answer 1

One simple way to do this would be to break this into several steps:

var sizeSorter = function(a, b) {return a - b};
var sizes = data.reduce(function(acc, item) {
    (acc[item.size] || (acc[item.size] = [])).push(item.width);
    return acc;
}, {}); //=> {8: ['M', 'W'], '6.5': ['W', 'M'], '7.5': ['W']}
Object.keys(sizes).sort(sizeSorter).map(function(size) {
    return {size_new: size, width_group: sizes[size]};
});

That sorting is necessary because the keys will be sorted in Array order, with small numbers like '8' before strings like '6.5'.

Answer 2

You need to search if you have already added a specific size and then update only its width. Otherwise insert a new object

var _x = x.reduce(function(p,v){
    var existing = p.filter(function(item){return item.new_size === v.size})[0];
    if (existing){
        existing.width_group.push( v.width );
    } else {
        p.push( {
            new_size: v.size,
            width_group:[v.width]
        } );
    }
    return p;
},[]);

Demo at http://jsfiddle.net/ogrqg412/3/