init table in join() without init of underlying t_columns

cpp/perspective/src/cpp/data_table.cpp

@@ -99,26 +99,28 @@ t_data_table::name() const {
 }
 
 void
-t_data_table::init() {
+t_data_table::init(bool make_columns) {
     PSP_TRACE_SENTINEL();
     LOG_INIT("t_data_table");
     m_columns = std::vector<std::shared_ptr<t_column>>(m_schema.size());
 
-#ifdef PSP_PARALLEL_FOR
-    tbb::parallel_for(0, int(m_schema.size()), 1,
-        [this](int idx)
-#else
-    for (t_uindex idx = 0, loop_end = m_schema.size(); idx < loop_end; ++idx)
-#endif
-        {
-            const std::string& colname = m_schema.m_columns[idx];
-            t_dtype dtype = m_schema.m_types[idx];
-            m_columns[idx] = make_column(colname, dtype, m_schema.m_status_enabled[idx]);
-            m_columns[idx]->init();
-        }
-#ifdef PSP_PARALLEL_FOR
-    );
-#endif
+    if (make_columns) {
+    #ifdef PSP_PARALLEL_FOR
+        tbb::parallel_for(0, int(m_schema.size()), 1,
+            [this](int idx)
+    #else
+        for (t_uindex idx = 0, loop_end = m_schema.size(); idx < loop_end; ++idx)
+    #endif
+            {
+                const std::string& colname = m_schema.m_columns[idx];
+                t_dtype dtype = m_schema.m_types[idx];
+                m_columns[idx] = make_column(colname, dtype, m_schema.m_status_enabled[idx]);
+                m_columns[idx]->init();
+            }
+    #ifdef PSP_PARALLEL_FOR
+        );
+    #endif
+    }
 
     m_init = true;
 }
@@ -639,21 +641,27 @@ t_data_table::join(std::shared_ptr<t_data_table> other_table) const {
     } 
 
     std::shared_ptr<t_data_table> rval = std::make_shared<t_data_table>(
-        "", "", schema, get_capacity(), BACKING_STORE_MEMORY);
-    rval->init();
+        "", "", schema, DEFAULT_EMPTY_CAPACITY, BACKING_STORE_MEMORY);
+
+    // init() without initializing the t_columns on the returned table, as
+    // they will be immediately replaced by the columns from the tables
+    // we are joining together.
+    rval->init(false);
 
     // borrow columns from the current table
     for (const std::string& column : m_schema.m_columns) {
         rval->set_column(column, get_column(column));
     }
 
+    // and the columns we need from the other table
     for (const std::string& column : other_columns) {
         rval->set_column(column, other_table->get_column(column));
     }
 
-    // don't set size on the columns - they are already of equal size, and we
-    // don't want to mutate the columns.
+    // Set size and capacity on the table only - don't mutate any of the
+    // columns.
     rval->set_table_size(size());
+    rval->set_capacity(std::max(get_capacity(), other_table->get_capacity()));
 
     return rval;
 }

cpp/perspective/src/include/perspective/data_table.h

@@ -69,7 +69,12 @@ class PERSPECTIVE_EXPORT t_data_table {
         t_uindex init_cap, t_backing_store backing_store);
     ~t_data_table();
 
-    void init();
+    /**
+     * @brief Initialize the `t_data_table`. If `make_columns` is True (the
+     * default option), construct and initialize the `t_column`s for the
+     * table.
+     */
+    void init(bool make_columns = true);
 
     const std::string& name() const;
 

python/perspective/perspective/tests/table/test_view_expression.py

@@ -81,6 +81,43 @@ def data():
         result = view.to_dict()
         assert result["123"] == [123 for _ in range(300)]
 
+    def test_view_streaming_expression_limit(self):
+        def data():
+            return [{"a": random()} for _ in range(55)]
+
+        table = Table(data(), limit=50)
+        view = table.view(expressions=["123"])
+
+        for i in range(5):
+            table.update(data())
+
+        assert table.size() == 50
+        result = view.to_dict()
+        assert result["123"] == [123 for _ in range(50)]
+
+    def test_view_streaming_expression_one(self):
+        def data():
+            return [{"a": random()} for _ in range(50)]
+
+        table = Table(data())
+        view = table.view(row_pivots=["c0"], expressions=['//c0\n"a" * 2'])
+
+        for i in range(5):
+            table.update(data())
+
+        assert table.size() == 300
+
+    def test_view_streaming_expression_two(self):
+        def data():
+            return [{"a": random()} for _ in range(50)]
+
+        table = Table(data())
+        view = table.view(row_pivots=["c0"], column_pivots=["c1"], expressions=['//c0\n"a" * 2', "//c1\n'new string'"])
+
+        for i in range(5):
+            table.update(data())
+
+        assert table.size() == 300
 
     def test_view_expression_create_no_alias(self):
         table = Table({"a": [1, 2, 3, 4], "b": [5, 6, 7, 8]})