public Dataset<Row> buildPairsForM0Prep(Dataset<Row> df, Dataset<Row> dfOld, GlentParams params) {
        dfOld = dfOld
                .where(col("part").equalTo(params.glentDfM0PrepPartOld))  // limit to previous portion of M0Prep dataframe
                .drop(col("part"));

        Column oldTsCondition = null;
        if (dfOld.isEmpty()) {
            oldTsCondition = lit(true);
        } else {
            Row[] oldTsRows = dfOld.agg(max("q1_ts").alias("tsmax")).collect();
            int fieldIdx = oldTsRows[0].fieldIndex("q1_ts");
            oldTsCondition = col("q2.ts").gt(oldTsRows[0].getInt(fieldIdx)); // latest timestamp of the records in previous portion of M0Prep
        }
                                                                        // to avoid double counting

        df = df
              .withColumn("suggCount", lit(1))
              .withColumn("part", lit(params.glentDfM0PrepPartNew))
              .where(oldTsCondition.and(col("q1.ts").gt(params.logTsFrom)).and(col("q1.ts").lt(params.logTsTo)))
              .select(col("q1.query").alias("q1_query"), col("q1.queryNorm").alias("q1_queryNorm"), col("q1.queryType").alias("q1_queryType"),
                      col("q1.wikiid").alias("q1_wikiid"), col("q1.lang").alias("q1_lang"), col("q1.source").alias("q1_source"),
                      col("q2.query").alias("q2_query"), col("q2.queryNorm").alias("q2_queryNorm"), col("q2.queryType").alias("q2_queryType"),
                      col("q2.wikiid").alias("q2_wikiid"), col("q2.lang").alias("q2_lang"), col("q2.source").alias("q2_source"),
                      col("q1.ts").alias("q1_ts"), col("q1.hitsTotal").alias("q1_hitsTotal"), col("q2.hitsTotal").alias("q2_hitsTotal"),
                      col("q1q2LevenDist"), col("suggCount"), col("part"));
        if (!dfOld.isEmpty())
            df = df.union(dfOld);                                                   // add previous M0Prep

//	creates new M0Prep
        return df
                .groupBy("q1_query", "q1_queryNorm", "q1_queryType", "q1_wikiid", "q1_source",
                         "q2_query", "q2_queryNorm", "q2_queryType", "q2_wikiid", "q2_source", "q1q2LevenDist")
                .agg(
                    max("q1_ts").alias("q1_ts"),
                    max("q1_hitsTotal").alias("q1_hitsTotal"),
                    max("q2_hitsTotal").alias("q2_hitsTotal"),
                    sum("suggCount").alias("suggCount"))
                .select(col("q1_query"), col("q1_queryNorm"), col("q1_queryType"), col("q1_wikiid"), col("q1_lang"), col("q1_source"),
                        col("q2_query"), col("q2_queryNorm"), col("q2_queryType"), col("q2_wikiid"), col("q2_lang"), col("q2_source"),
                        col("q1_ts"), col("q1_hitsTotal"), col("q2_hitsTotal"), col("q1q2LevenDist"), col("suggCount"), col("part"));
    }