Recursive variable problem

nurseryboy

I have a function that I am trying to add up some values in an hierarachy. I'm running into the problem that it is not keeping the value when it loops. Here is the code:

function project_addPrice($parent, $level, $price) {
       $query = DB_query("SELECT id,price FROM project_data WHERE parent='$parent'"); 
       while ($A = DB_fetchArray($query)) { 
              $price = $price + $A['price'];
              project_addPrice($A['id'], $level+1, $price); 
       } 
       return $price;
}

As you can see, I am trying to get $price to be added onto itself each time it goes through, but for some reason, it is not. I currently have 4 records in the database, and it looks something like this:

Record1
----Record2
--------Record3
----Record4

For each one, the value of $A['price'] is equal to 1. So, $price should be returned with the value of 4. But, the value of 1 is always returned.

All I need is for the total of all 4 prices to be returned. Maybe I am going about this the wrong way.

Either way, I cannot figure this out for the life of me, and any help would be greatly appreciated.

Thanks.

Matt

gufmn

I'm guessing it could be because $price is being redeclared everytime your loop executes. Try putting $price = 0; just before entering your loop.

nurseryboy

Hello,

Thanks. I just tried that and it didn't make a difference. I would think that $price would be carried, as it is set when calling the function, and I actually do think that $price is carried - just like $A['id'] is. I know that works, as it does loop through the database correctly.

I was thinking that maybe the last loop checks for any children of the parent, and since there isn't any, $A['price'] equals 0. But, that shouldn't matter, as 0 plus a number is still that number, and that number should be the sum of all the previous loops.

For some reason, $price doesn't add up right at the end, and doesn't get out of the loop correctly.

If anyone has any suggestions on how to aquire the sum of the hierarchy (recursive) a different way, please let me know as well. I know this is done all the time, I just can't figure it out myself.

Thanks.

MikeSnead

try echoing the value of $price at various places in the function... try and see if you can tell where things are going wrong.

Also, how are you calling the function initially?... it might not matter but I'm just curious 🙂

nurseryboy

Ok. Echoing after the prices have been added, but before the function is called again, like this:

function project_addPrice($parent, $level, $price) {

   $query = DB_query("SELECT id,price FROM project_data WHERE parent='$parent'"); 
   while ($A = DB_fetchArray($query)) { 
          $price = $price + $A['price'];
    --> echo 'ID: ' .$A['id']. ' Price: ' .$price. '<br>';
          project_addPrice($A['id'], $level+1, $price); 
   } 
   //return $price;
}

This returns the correct ID's in the correct order, and looks something like this:

ID: 1 Price: 1
ID: 2 Price: 2
ID: 4 Price: 3
ID: 3 Price: 3

Remember that the order of these are:

ID:1
----ID:2
--------ID:4
----ID:3

So everything seems to be correct, and $price adds up, except for the last loop (last one should be 4). But, if I comment out the echo line, and uncomment the return $price line, all I get is 1.

I initially call the function by:

$price = project_addPrice('', 0, 0);
echo $price;

MikeSnead

Try this:


function project_addPrice($parent, $level, $price) {
       $query = DB_query("SELECT id,price FROM project_data WHERE parent='$parent'"); 
       while ($A = DB_fetchArray($query)) { 
              $price = $price + $A['price'];
              $price += project_addPrice($A['id'], $level+1, $price); 
       } 
       return $price;
}

I think the problem is that you are not using the return value in any of the recursive calls. Adding that "$price +=" infront of the recursive call should fix it I think. The lack of it makes sense for the type of problem you are having.

gufmn

ID: 1 Price: 1
ID: 2 Price: 2
ID: 4 Price: 3
ID: 3 Price: 3

You said the value for each $A['price'] entry was 1. If that were the case, wouldn't it be ID: 3 Price: 4?

If MikeSnead's suggestion doesn't fix it, maybe try a print_r($A); just to make sure the data returned is what it should be.

nurseryboy

Mike,

Using:

$price += project_addPrice($A['id'], $level+1, $price);

returns a value of 19.. I'm not sure where that number comes from..

gufmn,
Using print_r($A) in the loop returns this:

Array ( [0] => 1 [id] => 1 [1] => 1 [price] => 1 )
Array ( [0] => 2 [id] => 2 [1] => 1 [price] => 1 )
Array ( [0] => 4[id] => 4 [1] => 1 [price] => 1 )
Array ( [0] => 3 [id] => 3 [1] => 1 [price] => 1 )

Price is shown as 1 for each, so that looks correct.

Haha, all I need to be able to do is get all those prices added together and returned by the function. Who would think it would be this hard?

And yes, the final price should be 4 in this:

ID: 1 Price: 1
ID: 2 Price: 2
ID: 4 Price: 3
ID: 3 Price: 3

gufmn

Your getting 19 because of the recursive function call. If all you need to do is add those values, just comment out the:

$price += project_addPrice($A['id'], $level+1, $price);

Unless you absolutely have to iterate over $level. But according to your question, you don't.

wempy

This is because everytime you enter the function you read every row returned from the db.
So for each row returned you enter the function again and read each row again, so for 4 rows returned you are reading (adding together the prices) 4 times.
I'm not sure that this is what you want to do. Are you just trying to find the total sum of all the returned rows from the DB, if so then the sql statement SUM(field_name) may be more what you require.

nurseryboy

I do need to add those values (price), but the only way I can see to do that is by looping through each record in the database. But remember, it's a hierarchy, and I cannot just select all records that have a common parent and add the values together.

Example:

ID: 1 Parent: 0 Price: 1
----ID: 2 Parent: 1 Price: 1
--------ID: 4 Parent: 2 Price: 1
----ID: 3 Parent: 1 Price: 1

I can't just select all that have a parent of 0, or 1, etc., and get the values, and the number of sub-children is unlimited, so I can't hard code each loop either.

Maybe I'm not making any sense, or I'm not understanding what you guys mean. I apologize if that is the case.

wempy

No, it is I who should apologise, I didn't fully understand the layout of the table hierarchy.

now I do the following may help

function project_addPrice($parent,$level)
{
    $price=0;
    $query = DB_query("SELECT id,price FROM project_data WHERE parent='$parent'");
    while ($A = DB_fetchArray($query)) { 
        $price =$A['price'];
        $price += project_addPrice($A['id'],$level+1);
    }
    return $price;
}

The $level variable is only used to show the recursion level, the $price variable doesn't need to be passed to the function as it is added to the total when it returns as it is the return value of the function (if that makes sense).

MikeSnead

Well... I set up a database and some functions to try and emulate a situation. The following code worked for me in adding the values correctly.

function project_addPrice( $parent , $level , $price )
{
	$query = db_query("SELECT id,price FROM project_data WHERE parent='$parent'");
	while ( $row = fetch_array($query) )
	{
		$price += $row['price'];
		project_addPrice($row['id'], $level+1, &$price);
	}

return $price;
}

The function names are a little off, but you can fix that easy 🙂

gufmn

wempy, nice job. Heh, I actually just came to the same conclusion. However, I was passing a 0 back as $price in the recursion just in case...... for some reason...... it...... needed to..... be there.... for..... something.....I don't know why 😃

nurseryboy

Haha, thanks wempy. I actually didnt see your post and went straight to Mike's, so I got to try his first. Here's the conclusion:

Mike,

After looking at your code, the only thing different (other than some of the names) that I could find, was the & in front of $price when calling the function again. I added that to my code, and it works!

Might I ask what that & does? It made all the difference.

Thanks to all of you!