PHP - Unexpected Behavior in Nested foreach Loop

Question

Some Background

I have 2 arrays with the following information:

$x = [
    ['name' => 'Fred', 'ykey' => 'A', 'rank' => '1', 'VIP' => '1'],
    ['name' => 'Fred', 'ykey' => 'B', 'rank' => '2', 'VIP' => '1'],
    ['name' => 'Joe', 'ykey' => 'A', 'rank' => '1', 'VIP' => '1'],
    ['name' => 'Joe', 'ykey' => 'B', 'rank' => '2', 'VIP' => '1'],
    ['name' => 'Frank', 'ykey' => 'A', 'rank' => '1', 'VIP' => '0'],
    ['name' => 'Frank', 'ykey' => 'B', 'rank' => '2', 'VIP' => '0']
]

and

$y = [
    'A' => [
        'hasVIPmember' => false,
        'slots' = [] //X elements will be placed here
    ]
    'B' => [
        'hasVIPmember' => false,
        'slots' = [] //X elements will be placed here
    ]

The goal is to place each of the elements in $x into $y with only one VIP member. I have a method to place the VIP members and then one to place everyone else. The information in $x is obtained from a database. The '1' in VIP means true.

The Problem

The problem I am having is outlined in the comments in the code below.

for($i = 1; $i <= 2; $i++){
    foreach($x as $z){
        //all Xs are seen here (after all iterations complete)
        if($z['VIP'] == 1 && $z['rank'] == $i){
            //Only Fred and Joe elements of X are shown here. (after all iterations complete)
            if(!($y[$z['ykey']]['hasVIPmember'])){
                //Only 'Fred' elements are shown here. Why?(after all iterations complete)
                $y[$z['ykey']]['slots'][]= $z;
                $y[$z['ykey']]['hasVIPmember'] = true;
            }
        }
    }
}

So the problem is, as you can see from the comments, when I perform if(!($y[$z['ykey']]['hasVIPmember'])){...} I only see the elements with the name "Fred" and, consequently, Fred is placed in both A and B.

The Question

Why is the list of items that are iterated through narrowed further in the final if statement? Is there any way to correct this behavior?

well, you never change hasVIPmember inside the loop, so even after you add a vipmember, you'll just keep adding more vip members,b ecause you never reset the flag to say one was added previously. — Marc B
– Marc B, Commented Sep 4, 2015 at 18:40
@MarcB Thanks for pointing that out. I actually do have that in my original code. I just missed it when I moved it here. — rabidhamper7
– rabidhamper7, Commented Sep 4, 2015 at 18:44

BinaryPatrick · Accepted Answer · 2015-09-04 19:11:16Z

4

When you run the iteration Fred is first for both ranks 1 and 2. As it runs, it adds Fred to $y and then skips over the rest because at that point $y[hasVIPmember] is true. You would need to find a way to invalidate Fred from the running after he is added to any $y by using some kind of counter or key, or change your data set.

$used = NULL;
for($i = 1; $i <= 2; $i++){
    foreach($x as $z){
        //all Xs are seen here (after all iterations complete)
        if($z['VIP'] == 1 && $z['rank'] == $i){
            //Only Fred and Joe elements of X are shown here. (after all iterations complete)
            if(!($y[$z['ykey']]['hasVIPmember'])){
                // looks for used
                if (!($z['name'] == $used)) {
                    $y[$z['ykey']]['slots'][]= $z;
                    $y[$z['ykey']]['hasVIPmember'] = true;
                    $used = $z['name']; //add Fred to the used name list
                }

            }
        }
    }
}

edited Sep 4, 2015 at 19:11

answered Sep 4, 2015 at 19:04

BinaryPatrick

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2 Comments

rabidhamper7 Over a year ago

Thanks for the fast answer! if( ... $z['rank'] == $i){...} prevents that from happening. I am seeing the following at the second comment (after the first if statement): When $i = 1 I see the first entry for Fred and then the first entry for Joe. When $i = 2 I see the second entry for Fred and then the second entry for Joe.

rabidhamper7 Over a year ago

After rereading your answer, I found that you were correct. Thanks so much for your help!

Golden_flash · Accepted Answer · 2015-09-04 19:30:23Z

2

Reason for the unexpected behavior is that you are using

$y[$z['ykey']]['hasVIPmember'] = true;

This lead to set hasVIPmember = true for all names in $x that has ykey='A' in the first iteration.Therefore after fred has been entered joe is skipped.

Similarly it sets hasVIPmember = true for all names in $x that has ykey='B' in the second iteration.

Even if you had more names in $x they all would have been excluded.

This code gives the desirable output ,

<?php

$x = [
['name' => 'Fred', 'ykey' => 'A', 'rank' => '1', 'VIP' => '1'],
['name' => 'Joe', 'ykey' => 'A', 'rank' => '1', 'VIP' => '1'],
['name' => 'Fred', 'ykey' => 'B', 'rank' => '2', 'VIP' => '1'],
['name' => 'Joe', 'ykey' => 'B', 'rank' => '2', 'VIP' => '1'],
['name' => 'Frank', 'ykey' => 'A', 'rank' => '1', 'VIP' => '0'],
['name' => 'Frank', 'ykey' => 'B', 'rank' => '2', 'VIP' => '0']
];

$y = [
'A' => [ 'hasVIPmember' => false , 'slots' => []  ],
'B' => [ 'hasVIPmember' => false , 'slots' => []  ]

 ];


for($i = 1; $i <= 2; $i++){
foreach($x as $z){
    //all Xs are seen here (after all iterations complete)
    if($z['VIP'] == 1 && $z['rank'] == $i){
       //Only Fred and Joe elements of X are shown here. (after all iterations complete)
        if(!($y[$z['ykey']]['hasVIPmember']))
          {
          echo $z['name']; // printing to check the name 
          echo $z['ykey']; // printing to check the ykey
          echo "<br>";  
          $y[$z['ykey']]['slots'][]= $z;

    }

}

}
}

?>

answered Sep 4, 2015 at 19:30

Golden_flash

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2 Comments

rabidhamper7 Over a year ago

I need to have only 1 VIP member in A and 1 VIP member in B. That is why I have that flag there, otherwise I will get multiples in each.

rabidhamper7 Over a year ago

That's correct. I failed to say that order was important in my question. Sorry about that.

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