PHP Create Associative Array from two arrays

Question

I need to push a second array into the first array by matching "cat_id" in the first array to "parent_id" in the second array.

I have the first array - $categories:

[
  {
    "cat_id": "350",
    "parent_id": "0",
    "cat_name": "Category 1"
  }
]

And a second array - $topics:

[
  {
    "cat_id": "351",
    "parent_id": "350",
    "cat_name": "Topic 1",
  },
  {
    "cat_id": "352",
    "parent_id": "350",
    "cat_name": "Topic 2",
  }
]

And I want this:

[
  {
    "cat_id": "350",
    "parent_id": "0",
    "cat_name": "Category 1",
    "topics": [
        {
          "cat_id": "351",
          "parent_id": "350",
          "cat_name": "Topic 1",
        },
        {
          "cat_id": "352",
          "parent_id": "350",
          "cat_name": "Topic 2",
        }
    ]
  }
]

I'm thinking that an embeded foreach loop might be the answer, but still sifting through all of the PHP array functions to try an figure out if there is an existing function that just does this: http://php.net/manual/en/ref.array.php

Sounds like you need to filter the second array on matching "parent_id"s and set that array to the value of the first array's "topics". — Sunny Patel
– Sunny Patel, Commented Jul 11, 2016 at 19:29
You need to learn how to use basic tools to accomplish things. e.g. swing_hammer() and twist_screwdriver() instead of flailing around for build_a_house() — Marc B
– Marc B, Commented Jul 11, 2016 at 19:30
in the initial array -> "cat_id": "350", , in the expected array "cat_id": "222", Why? — RomanPerekhrest
– RomanPerekhrest, Commented Jul 11, 2016 at 19:33

Ben Shoval · Accepted Answer · 2016-07-11 21:29:08Z

2

The short answer is:

foreach ( $categories AS &$category ) {
  foreach ( $topics AS $topic ) {
    if ( $category[ 'cat_id' ] == $topic[ 'parent_id' ] ) {
      $category[ 'topics' ][] = $topic;
    }
  }
}

This full script should (I hope) demonstrate the behavior you're after.

<?php

$categories = array(
    [
      "cat_id" => "350",
      "parent_id" => "0",
      "cat_name" => "Category 1",
      "topics" => []
    ]
  );

$topics = array (
    [
      "cat_id" => "351",
      "parent_id" => "350",
      "cat_name" => "Category 1 Topic 1",
    ],
    [
      "cat_id" => "352",
      "parent_id" => "350",
      "cat_name" => "Category 1 Topic 2",
    ]
  );

foreach ( $categories AS &$category ) {
  foreach ( $topics AS $topic ) {
    if ( $category[ 'cat_id' ] == $topic[ 'parent_id' ] ) {
      $category[ 'topics' ][] = $topic;
    }
  }
}

echo '<pre>';
print_r( $categories );
echo '</pre>';

?>

edited Jul 11, 2016 at 21:29

answered Jul 11, 2016 at 19:45

Ben Shoval

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11 Comments

webmaster_sean Over a year ago

Thanks for your answer Ben, sorry I should have been more specific, I've updated my question..

Ben Shoval Over a year ago

I've updated my answer to reflect your updated question. Hope it helps!

webmaster_sean Over a year ago

Hey Ben, I think this is close but it ends up repeating the first object per new topic as another object so I have redundant entry_id entries... this seems trivial because you should be able to say "if this key value matches this key value push this object into this array... Javascript libraries like Lodash these things are easy!

Ben Shoval Over a year ago

Hi Sean - If you could post some more of your sample arrays, I can likely figure out what's going on. You'll need to put it in your question or on pastebin with a link to it here, since comments are limited in characters. - Ben

Ben Shoval Over a year ago

Glad I can help. And again, if you'd like to share the data, the solution is likely pretty simple... I deal with a lot of very dirty data!

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