Question about php foreach

<?php
$post_ids = $wpdb->get_col("SELECT comment_post_ID FROM $wpdb->comments WHERE user_id = $current_user->ID AND comment_approved = '1' ");
foreach($post_ids as $post_id) {
$shedeg .= "$post_id, ";
}
echo $shedeg;
?>

PHP:

As you see this code adds , symbol to every $post_id value. How can I prevent adding it to the last value only.

Now the result is:
1, 2, 3, 4, 5,

And I need it to be:

1, 2, 3, 4, 5

Thanks in advance

 

<?php
$post_ids = $wpdb->get_col("SELECT comment_post_ID FROM $wpdb->comments WHERE user_id = $current_user->ID AND comment_approved = '1' ");
foreach($post_ids as $post_id) {
$shedeg .= "$post_id, ";
}
$shedeg = substr($shedeg, 0, -1);
echo $shedeg;
?>

add new line (bolded)
rep me up

 

Or use trim, for example:

$shedeg = trim($shedeg, ",");

PHP:

 

I would do that like this

<?php
$post_ids = $wpdb->get_col("SELECT comment_post_ID FROM $wpdb->comments WHERE user_id = $current_user->ID AND comment_approved = '1' ");
$shedeg='';
foreach($post_ids as $post_id) {
$shedeg .= (('' === $shedeg)?', ':'').$post_id;
}
echo $shedeg;
?>

PHP:

PS
I believe $shedeg = trim($shedeg, ",");
won't work since the last char is ' ' (space) not comma.

 

Oh, thanks to point out that... it should be this then

$shedeg = trim($shedeg, ", ");

PHP:

 

Guys, there's a function specific to this:

$shedeg = implode(',', $shedeg); 

Code (markup):

There, no need to complicate matters