Sorting data into mulit-dimensional, hierarchical array with PHP

Question

I need to sort an array of objects hierarchically. The data looks like this:

array (size=54)
  0 => 
    object(stdClass)[786]
      public 'term_id' => string '1' (length=3)
      public 'name' => string 'Boots' (length=25)
      public 'parent' => string '0' (length=3)
  1 => 
    object(stdClass)[785]
      public 'term_id' => string '2' (length=3)
      public 'name' => string 'Dresses' (length=25)
      public 'parent' => string '1' (length=3)
  2 => 
    object(stdClass)[786]
      public 'term_id' => string '3' (length=3)
      public 'name' => string 'Scarves' (length=25)
      public 'parent' => string '2' (length=3)
  3 => 
    object(stdClass)[785]
      public 'term_id' => string '4' (length=3)
      public 'name' => string 'Gloves' (length=25)
      public 'parent' => string '1' (length=3)

I want to create a multidimensional array that would show this hierarchy of "parent and children". The parent property of each object refers to the term_id of another object.

The result would look something like this:

array (size=54)
  0 => 
    object(stdClass)[786]
      public 'term_id' => string '1' (length=3)
      public 'name' => string 'Boots' (length=25)
      public 'parent' => string '0' (length=3)
      public 'children' => array (size=2)
            0 => 
                object(stdClass)[785]
                  public 'term_id' => string '2' (length=3)
                  public 'name' => string 'Dresses' (length=25)
                  public 'parent' => string '1' (length=3)
                  public 'children' => (size=1)
                      0 => 
                        object(stdClass)[786]
                          public 'term_id' => string '3' (length=3)
                          public 'name' => string 'Scarves' (length=25)
                          public 'parent' => string '2' (length=3)
            1 =>
                object(stdClass)[785]
                  public 'term_id' => string '4' (length=3)
                  public 'name' => string 'Gloves' (length=25)
                  public 'parent' => string '1' (length=3)

So far I have come up with this code:

$sortedCategories = array();
foreach($shopCategories as $shopCategory) {       
    $tmp = $shopCategory;
    foreach($shopCategories as $category) {
        if ($tmp->term_id == $category->parent) {
            $tmp->children[] = $category;
            $sortedCategories[] = $tmp;
        } 
    }
}

,but I cannot get it work with the multi-level hierarchy.

How can I sort the data to achieve the desired result?

kainaw · Accepted Answer · 2015-04-02 14:47:53Z

4

I would use a recursive function. It isn't really sorting that you are doing. You are building a tree structure. Assume your original objects are in an array called $a and you want the new tree to be called $b. What this function does is add everyone who is a child of the current parent you are working on. Every time it adds a child, it also calls itself to add that object's children. Hence, the recursion. You start with a parent of 0, which I assume means "no parent".

$b = build_tree($a);

function build_tree(&$a, $parent=0)
{
    $tmp_array = array();
    foreach($a as $obj)
    {
        if($obj->parent == $parent)
        {
            // The next line adds all children to this object
            $obj->children = build_tree($a, $obj->term_id);
            $tmp_array[] = $obj
        }
    }
    // You *could* sort the temp array here if you wanted.
    return $tmp_array;
}

answered Apr 2, 2015 at 14:47

kainaw

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4 Comments

luqo33 Over a year ago

Works perfectly. There is only one question I have. Why do you pass $a by reference to the build_tree function ? Is this necessary? Thank you a lot!

kainaw Over a year ago

I'm not going to alter $a in any way, so there is not reason to copy the entire array. That would just waste time and memory.

luqo33 Over a year ago

This is a very reasonable point. I must say the script that you proposed in your reply looks so neat and straightforward, but I find it difficult to rewalk its steps in my head. I definitely need practice..

kainaw Over a year ago

The walk is rather simple: Start with root (null) node. Add all the children to the root. When you add a child, right before you add it, add all children to that node. So, when you are adding those children, right before you add then, add all their children. Another note: I use recursion here because the recursion takes place in the middle of the function. If you ever write a recursive function and the recursion is at the end, you did it wrong.

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