Get authors who has posts in category - php

Question

I'm using Barcelona theme and I need to get authors who have posted in certain category.
In my author.php template I have:
$barcelona_authors = get_users( array(
'fields' => 'ID',
'who' => 'authors',
'order' => 'DESC',
'orderby'=> 'post_count'
) );
<?php
foreach ( $barcelona_authors as $barcelona_author_id ) {
barcelona_author_box( $barcelona_author_id, false );
}
?>
How to get authors who have posted to category ID 59?
For example I tried with:
$barcelona_authors = get_posts('category=59');
But I'm getting error. Any help?
ERROR:
Notice: Object of class WP_Post could not be converted to int in
/home/wp-includes/author-template.php on line 296

Answer 1

Your get_posts( 'category=59' ) code should work. I have tested the following on one of my test wordpress installation and it works (with a different category ID of course). If you get an error during the get_posts call you need to show us the error.
<?php
$category_posts = get_posts( 'category=59' );
$authors_ids = array();
$authors = array();
foreach( $category_posts as $cat_post ) {
$authors_ids[] = $cat_post->post_author;
}
// Not sure if you need more data than just the ID so here is what you need
// to get other fields.
foreach( $authors_ids as $id ) {
$user = get_user_data( $id );
// Display name: $user->display_name;
// Nice name: $user->user_nicename;
// etc...
}
?>

Answer 2

This was the solution for Barcelona theme:
$barcelona_posts = get_posts('cat=59');
$barcelona_author_ids = array();
foreach ( $barcelona_posts as $k => $v ) {
if ( ! in_array( $v->post_author, $barcelona_author_ids ) ) {
$barcelona_author_ids[] = $v->post_author;
}
}
$barcelona_authors = get_users( array(
'fields' => 'ID',
'who' => 'authors',
'order' => 'DESC',
'orderby'=> 'post_count',
'include' => $barcelona_author_ids
) );