Spark combine columns as nested array
<p>How can I combine columns in spark as a nested array?</p>

<pre><code>val inputSmall = Seq(
    ("A", 0.3, "B", 0.25),
    ("A", 0.3, "g", 0.4),
    ("d", 0.0, "f", 0.1),
    ("d", 0.0, "d", 0.7),
    ("A", 0.3, "d", 0.7),
    ("d", 0.0, "g", 0.4),
    ("c", 0.2, "B", 0.25)).toDF("column1", "transformedCol1", "column2", "transformedCol2")
</code></pre>

<p>To something similar as</p>

<pre><code>+-------+---------------+---------------+------- +
|column1|transformedCol1|transformedCol2|combined|
+-------+---------------+---------------+------ -+
|      A|            0.3|            0.3[0.3, 0.3]|
+-------+---------------+---------------+-------+
</code></pre>