Why doesn't this PHP recursive function return the value?

Question

I was working on an API for ustream which returns the following array

This is the function I used to go through the array as I want to fetch the [id] => 14659377 which is inside sourceChannel.But I am getting an empty value as a return value.What is the mistake I am making? can anyone please help me with it?

$getUsername = array();
function recursion($array) {
foreach ($array as $key => $value) {
      if($key==='sourceChannel'){
            $getId = $value['id'];
            //print_r($getId);
            return $getId;
          }
      if (is_array($value))
         recursion($value);
     }
}

$getUsername=recursion($resultsArray);
print_r($getUsername);

What's wrong with using `$array['results'][0]['sourceChannel']['id']`? — naththedeveloper, Jun 05 '13 at 07:05
Why is your code actually starting with `$getUsername = array();` !? $getUsername is overwritten later and nothing is done with it in between... — nl-x, Jun 05 '13 at 07:37
@nl-x its a block of code and some lines exist as I have been trying out things with it! :P — coderunner, Jun 05 '13 at 07:57

nl-x · Answer 1 · 2013-06-05T07:50:10.007

12

Your code is flawed because you need to change

recursion($value);

into

return recursion($value);

The return will take the answer back to the caller until the first caller is reached.

edit: The lesson here is that your function should ALWAYS return a value. So here is some more elaboration:

function recursion($array) {
    if (!is_array($array)) // check if what you're getting is an array!
        return null;
    foreach ($array as $key => $value) {
        if($key==='sourceChannel') {
            return $value['id'];
        }
        if (is_array($value)) {
            $result = recursion($value);
            if ($result !== null) {
                return $result;
            }
        }
    }
    return null; // this happens if all recursions are done and sourceChannel was not found
}

edited Jun 05 '13 at 07:50

answered Jun 05 '13 at 07:18

nl-x

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@coderunner please try my re-edited code. And if fails, update your question with your current code. It should work now. – nl-x Jun 05 '13 at 07:31
This doesnt work because you're blindly returning the first recursion you try in the loop. You should only be returning if your recursion call actually returns a non-null value - otherwise we want to continue through the loop. See my answer for a complete fix. – jcsanyi Jun 05 '13 at 07:36
@jcsanyi thanks, overlooked that indeed. I updated my answer. – nl-x Jun 05 '13 at 07:46
1

I also missed 'return' syntax right before calling rec function again. Thanks. – Jeaf Gilbert Apr 02 '16 at 09:35
1

return recursion() worked for me like a charm. Thanks @nl-x – Alvin Chettiar Jan 04 '18 at 08:42
oh! you are a life saver. return worked like a charm! – Chayan C May 08 '23 at 11:57

jcsanyi · Answer 2 · 2013-06-05T16:00:48.857

You're not doing anything with the return from your recursion call. It's a bit more complex than simply returning it, because you only want to cascade out if we actually found anything.

Try this:

function recursion($array) {
    foreach ($array as $key => $value) {
        if($key==='sourceChannel') {
            return $value['id'];
        }
        if (is_array($value)) {
            $rc = recursion($value);
            if (!is_null($rc)) return $rc;
        }
    }
    return null;
}

First, I added return null; to the end of the function - if we didn't find anything, we return null.

Then, when I recurse, I check the return value... if it's non-null, it means we found something and we want to return it. If it is null, we don't want to return - we want to continue the loop instead.

There's a `return null;` inside the loop. – Ja͢ck Jun 05 '13 at 07:55 — Ja͢ck, Jun 05 '13 at 07:55

score 1 · Answer 3 · answered Jun 05 '13 at 07:05

1

Try like this

foreach ($array['results'] as $key => $value) {
   if($key == "sourceChannel"){
        $getId = $value['id'];
        //print_r($getId);
        return $getId;
   }       
}

answered Jun 05 '13 at 07:05

GautamD31

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This answer might suit this case. But doesn't have recursion, and thus does not really answer the question. `Why doesn't this PHP recursive function return the value?` – nl-x Jun 05 '13 at 07:20
Why iterate over the array if you can also use `isset()`? And what happened to the recursive step? – Ja͢ck Jun 05 '13 at 07:23
Depends on what is to be expected. For now it would do. But then FDL's comment will even be better... `$array['results'][0]['sourceChannel']['id']` – nl-x Jun 05 '13 at 07:24
It doesn't work,I believe I will need to modify my function call like this... `$getUsername=recursion($resultsArray['results']);` right? but still I get an error for either index 'result' or foreach argument! where am I wrong? – coderunner Jun 05 '13 at 07:28
call like $getUsername=recursion($resultsArray); only – GautamD31 Jun 05 '13 at 07:30
`'sourceChannel'` is not a key in `$array['results']`, so this code will never return anything other than undefined. – Ja͢ck Jun 05 '13 at 07:42
Then what will be the 'sourceChannel'..?? – GautamD31 Jun 05 '13 at 08:35

Ja͢ck · Answer 4 · 2013-06-05T07:39:38.637

1

You could use iterators to make your function a whole lot easier:

function findSourceChannel($array)
{
    foreach (new RecursiveIteratorIterator(new RecursiveArrayIterator($array)) as $key => $value) {
        if ($key == 'sourceChannel') {
            return $value['id'];
        }
    }
    return null;
}

That said, I'm not sure why you can't just do a search like this:

foreach ($array['results'] as $result) {
    if (isset($result['sourceChannel'])) {
        return $result['sourceChannel']['id'];
    }
}
return null;

edited Jun 05 '13 at 07:39

answered Jun 05 '13 at 07:20

Ja͢ck

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Hey,thanks Jack are these classes inbuilt with the PHP version?Can I directly use them?Haven't tried them yet. – coderunner Jun 05 '13 at 07:25
yup Jack that search did the trick.Also,if `sourceChannel` is not a `key`(as you said in the above post) in the array how can I do it using the `RecursiveIteratorIterator` method? – coderunner Jun 05 '13 at 08:03
@coderunner In the meantime I've expanded my answer to include a method that doesn't even need recursion. Do check that out. – Ja͢ck Jun 05 '13 at 08:19
Yes, I mentioned in the previous post that it works and I just didn't think about it!! – coderunner Jun 05 '13 at 08:24

Why doesn't this PHP recursive function return the value?

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