Questions about appending data in PHP

Example:

<code>$a = "1,3,4";
</code>

How to append data to $a? Before appending, you need to check whether it contains the pre-added number. For example, 5 is not among them, then the result after appending is:

<code>$a = "1,3,4,5";
</code>

How to achieve this?

Reply content:

Example:

<code>$a = "1,3,4";
</code>

How to append data to $a? Before appending, you need to check whether it contains the pre-added number. For example, 5 is not among them, then the result after appending is:

<code>$a = "1,3,4,5";
</code>

How to achieve this?

<code>implode(',',array_unique(explode(',',$a)))</code>

Convert to array first, merge, remove duplicates, then convert back

Why not use an array? array_search() checks whether the memory exists. If it does not exist, push it to enter. Finally, impload(l