[lmi-commits] [lmi] master 337d81f 37/46: Make UponDeleteCells() more efficient for large censuses

[Greg Chicares]

branch: master
commit 337d81ff1d68d0f2ead26102ba5a89ca6ac01565
Author: Vadim Zeitlin <vadim@tt-solutions.com>
Commit: Vadim Zeitlin <vadim@tt-solutions.com>

    Make UponDeleteCells() more efficient for large censuses
    
    Operate on entire blocks, i.e. ranges of the selected rows, at once,
    rather than on the individual rows, as there are many fewer of the
    former than of the latter.
---
 census_view.cpp | 53 +++++++++++++++++++++++++++++++++--------------------
 1 file changed, 33 insertions(+), 20 deletions(-)

diff --git a/census_view.cpp b/census_view.cpp
index c213144..06a7bda 100644
--- a/census_view.cpp
+++ b/census_view.cpp
@@ -2727,13 +2727,33 @@ void CensusDVCView::UponDeleteCells(wxCommandEvent&)
 void CensusGridView::UponDeleteCells(wxCommandEvent&)
 {
     auto const n_items = grid_table_->GetRowsCount();
-    auto rows = grid_window_->GetSelectedRows();
-    // If no cell is selected then use the current row
-    if (rows.empty())
+
+    // Iterate over selected blocks, not rows, as this can be significantly
+    // more efficient: in a grid with 10,000 rows, the user can easily select
+    // all of them, but the selection consists of just a single block, so
+    // iterating over it is quick, while iterating over all the individual rows
+    // would take much longer.
+    auto sel_blocks = grid_window_->GetSelectedRowBlocks();
+
+    int n_sel_items = 0;
+
+    // If no rows are selected, use the current row.
+    if (sel_blocks.empty())
+        {
+        // Synthesize a block corresponding to the current row using 0 for the
+        // column values because we don't use them anyhow.
+        auto const cursor_row = grid_window_->GetGridCursorRow();
+        sel_blocks.push_back(wxGridBlockCoords{cursor_row, 0, cursor_row, 0});
+
+        n_sel_items = 1;
+        }
+    else // Compute the total number of selected rows
         {
-        rows.push_back(grid_window_->GetGridCursorRow());
+        for(auto const& block : sel_blocks)
+            {
+            n_sel_items += block.GetBottomRow() - block.GetTopRow() + 1;
+            }
         }
-    auto const n_sel_items = lmi::ssize(rows);
 
     if(n_items == n_sel_items)
         {
@@ -2770,33 +2790,26 @@ void CensusGridView::UponDeleteCells(wxCommandEvent&)
 
     auto const cursor_col = grid_window_->GetGridCursorCol();
 
-    std::sort(rows.begin(), rows.end());
-
     LMI_ASSERT(lmi::ssize(cell_parms()) == n_items);
 
     wxGridUpdateLocker grid_update_locker(grid_window_);
     grid_window_->ClearSelection();
 
-    int items_left = n_sel_items;
-    while(items_left > 0)
+    // Annoyingly, range-for can't be used to iterate in the reverse direction
+    // before C++20, so do it manually.
+    for(auto i = sel_blocks.rbegin(); i != sel_blocks.rend(); ++i)
         {
-        int cur_item = items_left - 1;
-        for(; 0 < cur_item; --cur_item)
-            {
-            if(rows[cur_item] - 1 != rows[cur_item - 1])
-                break;
-            }
-        int const count = items_left - cur_item;
-        items_left -= count;
+        auto const& block = *i;
+        auto const count = block.GetBottomRow() - block.GetTopRow() + 1;
 
-        auto const first = cell_parms().begin() + cur_item;
+        auto const first = cell_parms().begin() + block.GetTopRow();
         cell_parms().erase(first, first + count);
-        grid_window_->DeleteRows(cur_item, count);
+        grid_window_->DeleteRows(block.GetTopRow(), count);
         }
     LMI_ASSERT(lmi::ssize(cell_parms()) == n_items - n_sel_items);
 
     int const new_cursor_row(std::min
-        (rows.front()
+        (sel_blocks.front().GetTopRow()
         ,lmi::ssize(cell_parms()) - 1
         ));
     grid_window_->GoToCell(new_cursor_row, cursor_col);