将嵌套数组转换为逗号分隔的值列表

Question

I have a simple bit of JSON like this:

{
  "grinning": {
    "unicode": "1f600",
    "unicode_alternates": "",
    "name": "grinning face",
    "shortname": ":grinning:",
    "category": "people",
    "emoji_order": "1",
    "aliases": [

    ],
    "aliases_ascii": [

    ],
    "keywords": [
      "happy",
      "joy",
      "smile",
      "grin",
      "smiling",
      "smiley",
      "person"
    ]
  },
  "grimacing": {
    "unicode": "1f62c",
    "unicode_alternates": "",
    "name": "grimacing face",
    "shortname": ":grimacing:",
    "category": "people",
    "emoji_order": "2",
    "aliases": [

    ],
    "aliases_ascii": [

    ],
    "keywords": [
      "teeth",
      "grimace",
      "disapprove",
      "pain",
      "person"
    ]
  }
}

I can access the "unicode" and "name" elements via:

<?php
$str = file_get_contents('http://localhost/_testing/emoji/emoj1-test.json');

$json_a = json_decode($str, true);

foreach($json_a as $key => $val) {
    echo $val['unicode'];
    echo $val['name'];
}
?>

But I can't work out how I can get the "keywords" nested array into a variable containg the keywords held as a comma separated list of values.

I simplistically tried:

echo $val['keywords'];

But because that's an array, it returns this error:

Notice: Array to string conversion

I then tried:

echo $val['keywords'][0];

Which I think is along the right lines, but still doesn't return any data.

Answer 1

echo implode(',', $val['keywords']);