how to grab a "random" set of items from a loop in php

Im looping through some XML nodes, and say i have between 1 and 200 of these nodes.

How can i "randomly" select a maximum of 10 of these nodes. It has to be as most ten, but as few as 1.

This is what im working with now...

        $i = 0;
 开发者_如何学编程       foreach ($butters->users->user as $user) {
            if($i==10) break;
            $id = $user->id;
            $name = $user->screen_name;
            $profimg = $user->profile_image_url;
            echo "things";
            $i++;
        } 

The difficulty is that i don't know how many i will have, but would like the pool from which i select my "random" 10 to be from the entirety of however many are present.

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$randomPool = array_rand ( $butters->users->user, 10 );

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I'd get the 10 random indexes, then loop through those and get the nodes.

$indexes = array();
for($i = 0; $i< 10; $i++){
  $indexes[] = rand(0, $butters->users->length);
}

foreach($indexes as $index){
  $user = $butters->users->item($index);
  //do whatever with $user
}

You'll need to add a check to make sure that you have not already got the index when you add it to the $indexes array.

You could put this into one command, however you may end up with duplicates (unlikely depending on the amount of elements, but possible...

for($i = 0; $i< 10; $i++){
  $user = $butters->users->item(rand(0, $butters->users->length));
  //do something with $user
}

---

Put all users in an array, shuffle it and grab the first ten items:

$users = array[];
foreach ($butters->users->user as $user) {
    $users[] = &$user;
}
shuffle($users);
$tenRandomUsers = array_slice($users, 0, 10);

Maybe you can shorten the first step with just $users = (array) $butters->users->user.

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Create a random object (don't know the PHP specific code) then call it and compare with 10 / (total in the set). This means you should in theory select 10%, however it could be less, and your exiting code stops it from selecting more.

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Assuming you are using SimpleXML, you could use an XPath to get all the users. This will return an array and from that it should be cake.

Something like this should do:

$users  = $xml->xpath('//butters/users/user');
$random = array_rand($users, 10);

Someone might want to correct me on the Xpath though. Doing it from memory

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if you have some sort of strange self-implemented data structure for $users you might want to use reservior sampling -- Efficiently selecting a set of random elements from a linked list