How to get user ID's from multiple usernames?

Question

I am trying to produce user ID's from multiple specific usernames. The usernames are pulled from a profile field, and any number of usernames will be called. I want the user ID's from each of the users to be put into the 'include' of $args like 'include' => array( 1, 2),. What am I doing wrong?

// Search these Usernames
$usernames = array( user1, user2 );

// Fetch the User IDs
$prof_ids = array(); 
foreach ($usernames as $prof_id) {
    $user = get_user_by('user_login', $prof_id); 
    $prof_ids[] = $user->ID;
}

// WP_User_Query arguments
$args = array(
     'include' => $prof_ids,
);

I tried printing each variable to see where I'm going wrong, and these are their outputs:

$usernames = Array
$prof_ids = Array
$prof_id = user2
$user = 
$args = Array

Answer 1

Your call to get_user_by() has a small hiccup in it. It needs to be login rather than user_login

// Search these Usernames
$usernames = array('user1', 'user2');

// Fetch the User IDs
$prof_ids = array(); 
foreach ($usernames as $prof_id) {
    $user = get_user_by('login', $prof_id); 
    $prof_ids[] = $user->ID;
}

// WP_User_Query arguments
$args = array(
     'include' => $prof_ids,
);