使用公共值将两个表中的两个数组合并为一个数组

I'm trying to combine arrays generated from 2 different tables - 'articles' and 'article_categories'. The output of 'article_categories' is:

Array
(
[0] => Array
    (
        [id] => 0
        [title] => local
    )

[1] => Array
    (
        [id] => 1
        [title] => politics
    )

[2] => Array
    (
        [id] => 2
        [title] => economics
    )
)

The function code is:

public function newsGetCategoryList() {
        $result = $this->db->select('SELECT * FROM article_categories ORDER BY id');   
        return $result;
}

The output of 'articles' is:

Array
(
[0] => Array
    (
        [id] => 0
        [title] => Article 1
        [content] => content
        [category] => local
    )

[1] => Array
    (
        [id] => 1
        [title] => Article 2
        [content] => content
        [category] => local
    )

[2] => Array
    (
        [id] => 2
        [title] => Article 2
        [content] => content
        [category] => local
    )
)

The function code is:

public function newsGetCategoryArticles($category) {
       $result = $this->db->select('SELECT * FROM articles WHERE category_id = :category', array('category' => $category));            
       return $result;
    }

I need to insert 'articles' array into 'article_categories' so the output becomes:

Array
(
[0] => Array
    (
        [id] => 0
        [title] => local
        [articles] => Array
        (
        [0] => Array
            (
               [id] => 0
               [title] => Article 1
               [content] => content
               [category] => local
            )

        [1] => Array
            (
               [id] => 1
               [title] => Article 2
               [content] => content
               [category] => local
            )

        [2] => Array
            (
               [id] => 2
               [title] => Article 2
               [content] => content
               [category] => local
            )
        )
)
[1] => Array
    (
        [id] => 1
        [title] => politics
    )

[2] => Array
    (
        [id] => 2
        [title] => economics
    )
)

In other words, articles should be inside the category array if articles' category value matches to category's title.

I have tried applying array_push in foreach loop on 'article_categories' but I was only getting a separate array for each category entry, rather than the whole array. I have no ideas how to approach this.

Thanks

Found the solution myself. Had to change newsGetCategoryList()

public function newsGetCategoryList() {
        $array = $this->db->select('SELECT * FROM article_categories ORDER BY id');
        $result = array();
        foreach ($array as $value) {
            $articles = $this->newsGetCategoryArticles($value['title']);
            array_push($value, $articles);
            $result[] = $value;                
        } 
        return $result;
    }