code: public static Vec numericToStringVec(Vec src) {
      if (src.isCategorical() || src.isUUID())
        throw new H2OIllegalValueException("Cannot convert a non-numeric column"
            + " using numericToStringVec() ",src);
      Vec res = new MRTask() {
        @Override
        public void map(Chunk chk, NewChunk newChk) {
          if (chk instanceof C0DChunk) { // all NAs
            for (int i=0; i < chk._len; i++)
              newChk.addNA();
          } else {
            for (int i=0; i < chk._len; i++) {
              if (!chk.isNA(i))
                newChk.addStr(PrettyPrint.number(chk, chk.atd(i), 4));
              else
                newChk.addNA();
            }
          }
        }
      }.doAll(Vec.T_STR, src).outputFrame().anyVec();
      assert res != null;
      return res;
    }
docs: Create a new {@link Vec} of string values from a numeric {@link Vec}.
  
  Currently only uses a default pretty printer. Would be better if
  it accepted a format string PUBDEV-2211
  
  @param src a numeric {@link Vec}
  @return a string {@link Vec}