Add brackets to string in data frame
<p>I've got this data frame called df:</p>

<pre><code>ColumnA   ColumnB
String1   A
String2   A
String3   B
String4   A
...       ...
</code></pre>

<p>Every string in ColumnA have different lenght. I want to put values from ColumnA in brackets if value in ColumnB == A in the same row. If the value in ColumnB == B I want to add square brackets instead. So it will looks like:</p>

<pre><code>ColumnA     ColumnB
(String1)   A
(String2)   A
[String3]   B
(String4)   A
...         ...
</code></pre>

<p>What's the best way to achive that?</p>