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Version: Java (Groovy)

How to create a hierarchical tree table

This guide will show you how to create a hierarchical tree table. A tree table implements a tree structure in a table, with expandable nodes to see child-parent relationships.

Parent-child relationships are given in pairs of columns. Parent column values are expected to be found in the ID column as well. For instance, a row with Parent = A is a child of the row with ID = A. Nodes with Parent=null are children of the root, and visible in the initial expansion.

The basic syntax for creating a tree table is as follows:

resultWithNoOrphans = source.tree(idCol, parentCol)
resultWithOrphans = TreeTable.promoteOrphans(source, idCol, parentCol).tree(idCol, parentCol)

The resulting table initially only has the root node expanded. Nodes can be expanded by clicking on the right-facing arrow in a given cell. Doing so expands everything that is one level down from the selected node.

Examples​

Static data​

The first example creates two constituent tables, which are then joined together to form the source table. The ID and Parent columns in source are used as the ID and parent columns, respectively.

source = emptyTable(100).updateView("ID = i", "Parent = i == 0 ? NULL_INT : (int)(i / 4)")

result = source.tree("ID", "Parent")

Real-time data​

Tree tables work in real-time applications the same way as they do in static contexts. This can be shown via an example similar to the one above.

t1 = emptyTable(10_000).updateView("ID = i", "Parent = i == 0 ? NULL_INT : (int)(i / 10)")
t2 = timeTable("PT00:00:00.01").updateView("I = i % 10_000").lastBy("I")

source = t1.join(t2, "ID = I")

result = source.tree("ID", "Parent")

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Orphan nodes​

Rows in a tree table are considered "orphans" if their parent is not null and does not exist in the table. By default, these rows are omitted from the tree table altogether. In order to include orphans in a tree table, call promoteOrphans on the TreeTable interface, and call tree on the result of that invocation to ensure that the tree will contain the orphan nodes as children of the root.

import io.deephaven.engine.table.hierarchical.TreeTable

source = emptyTable(100).updateView("ID = i + 2", "Parent = i == 0 ? NULL_INT : i % 9")

resultNoOrphans = source.tree("ID", "Parent")
resultWithOrphans = TreeTable.promoteOrphans(source, "ID", "Parent").tree("ID", "Parent")