How to use array in function to get only value I want - php

Question

I am trying to work this function in wordpress theme the way where I can get value only what I want and not all to gather. I am not much familiar with using array in function so I need you expert help to make it works and I would really appreciate that.
Here is my code
function gallery_artist($arg=null, $arg2=null, $arg3=null){
global $png_gallery_meta;
$png_gallery_meta->the_meta();
$gallery = get_post_meta(get_the_ID(), $png_gallery_meta->get_the_id(), TRUE);
$gallery_value = $gallery['image_artist'];
$artist_info = $gallery_value;
$string = $artist_info;
$artist = substr($string, 0, stripos($string, "/") );
// getting first name and last name from user id
$author_first_name = get_userdata(basename($string))->first_name;
$author_last_name = get_userdata(basename($string))->last_name;
$author_full_name = $author_first_name . ' ' . $author_last_name;
$user_id = '<a href=" ' . get_author_posts_url(basename($string)) . ' " title="more submissions of ' . $author_first_name .' '. $author_last_name . ' " >' . $artist . '</a>';
$arg = $author_first_name;
echo $arg;
$arg2 = $author_last_name;
echo $arg2;
$arg3 = $user_id;
echo $arg3;
}
After than I want to use this function to get any value I want and not unnecessary to render all three to gather. Means if I want only first name than I pass value only for that and it will render only first name so on..
Here how I want to use something. but you can suggest any code and type of function I have no issue.
<?php call_user_func_array('gallery_artist', array('first_name','last_name','artist_id') ) ?>
Big Big thanks to you all..

Answer 1

Try replacing the bottom section with this:
if(!is_null($arg))
{
$arg = $author_first_name;
echo $arg;
}
if(!is_null($arg2))
{
$arg2 = $author_last_name;
echo $arg2;
}
if(!is_null($arg3))
{
$arg3 = $user_id;
echo $arg3;
}