Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/19479#discussion_r150391234 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/Statistics.scala --- @@ -275,6 +313,127 @@ object ColumnStat extends Logging { avgLen = row.getLong(4), maxLen = row.getLong(5) ) + if (row.isNullAt(6)) { + cs + } else { + val ndvs = row.getArray(6).toLongArray() + assert(percentiles.get.numElements() == ndvs.length + 1) + val endpoints = percentiles.get.toArray[Any](attr.dataType).map(_.toString.toDouble) + // Construct equi-height histogram + val bins = ndvs.zipWithIndex.map { case (ndv, i) => + HistogramBin(endpoints(i), endpoints(i + 1), ndv) + } + val nonNullRows = rowCount - cs.nullCount + val histogram = Histogram(nonNullRows.toDouble / ndvs.length, bins) + cs.copy(histogram = Some(histogram)) + } + } + +} + +/** + * This class is an implementation of equi-height histogram. + * Equi-height histogram represents the distribution of a column's values by a sequence of bins. + * Each bin has a value range and contains approximately the same number of rows. + * @param height number of rows in each bin --- End diff -- nit: one blank line before this.
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