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    <p>You can do the job in one pass using object as an associative array:</p> <pre><code>var test_items = [ { title:'child element 2.2', type:'e', id:6, parent:4 }, { title:'child element 2.1', type:'e', id:5, parent:4 }, { title:'container 1', type:'c', id:1, parent:0 }, { title:'container 2', type:'c', id:4, parent:0 }, { title:'child element 1.1', type:'e', id:2, parent:1 }, { title:'child element 1.2', type:'e', id:3, parent:1 }, { title:'element without parent A', type:'e', id:8, parent:0 }, { title:'element without parent B', type:'e', id:7, parent:0 } ]; function itemsToTree2( items ) { var tree2 = {}; for( var i=0; i&lt;items.length; ++i ) { var item = items[i]; if( item.type=='c' || item.parent==0 ) { if( !tree2[item.id] ) { var parent = { id:item.id, parent:0, children:[] }; tree2[item.id] = parent; } tree2[item.id].title = item.title; tree2[item.id].type = 'c'; } else { if( !tree2[item.parent] ) { var parent = { id:item.parent, parent:0, children:[] }; tree2[item.parent] = parent; } tree2[item.parent].children.push(item); } } return tree2; } var test_tree2 = itemsToTree2(test_items); console.log(test_tree2); </code></pre> <p>Not sure if it will be significantly faster... And if you know that every container will appear before its elements in the input data - the code above can be simplified:</p> <pre><code>function itemsToTree2( items ) { var tree2 = {}; for( var i=0; i&lt;items.length; ++i ) { var item = items[i]; if( item.type=='c' || item.parent==0 ) { item.children = []; tree2[item.id] = item; } else { tree2[item.parent].children.push(item); } } return tree2; } </code></pre> <p>If you need to alphabetically sort the tree (by title) levelwise (which is very often the case) you will need extra processing:</p> <pre><code>function sortTree2( tree2, comparator ) { var tree2array = []; for( var id in tree2 ) tree2array.push( tree2[id] ); tree2array.sort(comparator); for( var i=0; i&lt;tree2array.length; ++i ) tree2array[i].children.sort(comparator); return tree2array; } var sorted_tree2 = sortTree2( test_tree2, function(a,b) { return a.title &gt; b.title; }); console.log(sorted_tree2); </code></pre> <p>General solution for trees deeper than 2 levels exists too. It uses resembling approach and is not much more complex than this.</p>
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    1. POsorting items by parents and type
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    1. COThank you very much, your sorting is interesting and i'll be glad to use it later, but this time i wanted to add position number in properties of element.
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    2. CO@philosophocat The issue with sorting is that building any conventional presentation of a tree (implemented with identation, embedded html lists, tree control or etc) already requires partial ordering of tree items: all descendants of every node must succeed that node and preceed any of its siblings (or upper nodes). In other words, items must be ordered so that tree could be folded/unfolded without reordering items. There exist much more than one such ordering. In other words, tree can be sorted only "levelwise".
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    3. CO@philosophocat So, if you use position property there are three cases. 1) Position property values already respect tree structure - no further processing needed, just display items in position order, indenting elements. 2) Position properties are arbitrary and you like to sort categories on minimal position of their items (not always position of category itself) - presort items on position property, then run tree-forming function. 3) Position properties are arbitrary and you like to sort categories on thir own positions - run tree-forming function, than levelwise sort on position like on title
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