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remove precondition on aggregate such that empty slices are allowed #795

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Apr 22, 2020
Merged

remove precondition on aggregate such that empty slices are allowed #795

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2 changes: 0 additions & 2 deletions core/src/main/java/tech/tablesaw/table/TableSliceGroup.java
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,6 @@

package tech.tablesaw.table;

import com.google.common.base.Preconditions;
import com.google.common.base.Splitter;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.ListMultimap;
Expand Down Expand Up @@ -187,7 +186,6 @@ public Table aggregate(String colName1, AggregateFunction<?, ?>... functions) {
*/
@SuppressWarnings({"unchecked", "rawtypes"})
public Table aggregate(ListMultimap<String, AggregateFunction<?, ?>> functions) {
Preconditions.checkArgument(!getSlices().isEmpty());
Table groupTable = summaryTableName(sourceTable);
StringColumn groupColumn = StringColumn.create("Group");
groupTable.addColumns(groupColumn);
Expand Down
26 changes: 26 additions & 0 deletions core/src/test/java/tech/tablesaw/table/TableSliceGroupTest.java
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Expand Up @@ -21,6 +21,7 @@
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.IntStream;
import org.apache.commons.math3.stat.StatUtils;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
Expand Down Expand Up @@ -139,4 +140,29 @@ public void aggregateWithMultipleColumns() {
group.aggregate(ImmutableListMultimap.of("approval", exaggerate, "approval2", exaggerate));
assertEquals(aggregated.rowCount(), group.size());
}

/**
* Make sure that aggregations are allowed on empty tables. They should however just create new
* empty tables.
*
* <p>see <a href="https://github.com/jtablesaw/tablesaw/issues/785">Issue#785</a>
*/
@Test
public void aggregateWithEmptyResult() {
// drop all rows in order to carry out aggregation on an empty table
table = table.dropRows(IntStream.range(0, table.column(0).size()).toArray());

TableSliceGroup group = StandardTableSliceGroup.create(table, table.categoricalColumn("who"));
Table aggregated = group.aggregate("approval", exaggerate);
assertEquals(0, aggregated.rowCount(), "result should be empty");
assertEquals(2, aggregated.columnCount()); // 1 original column + the aggregation column

table.addColumns(table.categoricalColumn("approval").copy().setName("approval2"));
group = StandardTableSliceGroup.create(table, table.categoricalColumn("who"));

aggregated =
group.aggregate(ImmutableListMultimap.of("approval", exaggerate, "approval2", exaggerate));
assertEquals(0, aggregated.rowCount(), "result should be empty");
assertEquals(3, aggregated.columnCount()); // 2 original columns + the aggregation column
}
}