code: public DataSetBuilder random(String column, Function<Random,?> gen) {
      return set(column, () -> gen.apply(rng));
    }
docs: Set customized random filler.
  
  <p>
  The specified column will be filled with values that are obtained
  from a generator function. The generator function
  takes a {@link Random} instance as an argument and returns a value:
  it should use the generator to produce column values in deterministic
  fashion (in particular, the random number generator argument should not
  be re-seeded).
  </p>
  
  <p><b>Illustration of use</b></p>
  <p>The filler below will yield strings
  <code>"ID_0", ..., "ID_9"</code> with an uniform
  distribution:</p>
  <blockquote><pre>
  DataSet ds = ...;
  ...
  ds.random("SomeColumn", rng -&gt; "ID_" + rng.nextInt(10));
  </pre></blockquote>
  @param column Column name.
  @param gen Generator function.
  
  @return The builder instance (for chained calls).
  
  @see java.util.Random
  @see #random(String, int, int)
  @see #random(String, long, long)
  @see #random(String, float, float)
  @see #random(String, double, double)
  @see #random(String, Date, Date)
  @see #random(String, Time, Time)
  @see #random(String, Timestamp, Timestamp)