A Pig UDF that allows you to modify a map by adding additional key/value pairs

AddToMap.java

import java.io.IOException;
import java.util.Map;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.DataType;
import org.apache.pig.data.Tuple;

/**
 * Simple UDF to allow modifying an existing map[] datum
 *
 * Usage:
 *   FOREACH relation GENERATE AddToMap(m, "foo", "bar");
 *
 * Multiple key-value pairs can be included (similar to the builtin TOMAP)
 */
public class AddToMap extends EvalFunc<Map> {

    @Override
    public Map exec(Tuple tuple) throws IOException {
      // If tuple is null, has fewer than 3 values, or has an even number of values
      if (tuple == null || tuple.size() < 3 || (tuple.size() % 2 == 0)) {
        throw new IOException("Incorrect number of values.");
      }
      try {
        Map<String, Object> map = (Map<String, Object>) tuple.get(0);
        String key;
        Object value;
        for(int i=1; i<tuple.size(); i+=2) {
          key = (String)tuple.get(i);
          value = (Object)tuple.get(i+1);
          map.put(key, value);
        }
        return map;
      } catch (Exception e) {
        throw new IOException(e);
      }
    }

}