Keep the experiment identifiers map when slicing a reflection table. (#…

…2371)

Fixes #2276

newsfragments/2371.bugfix

@@ -0,0 +1 @@
+Keep the experiment identifiers map when slicing a reflection table

src/dials/array_family/boost_python/flex_table_suite.h

@@ -468,6 +468,20 @@ namespace dials { namespace af { namespace boost_python { namespace flex_table_s
       copy_to_slice_visitor<T> visitor(result, it->first, as);
       it->second.apply_visitor(visitor);
     }
+    if (self.contains("id")) {
+      /* note some tables contain id values of -1 for unindexed reflections
+      but the identifiers map only allows keys of type size_t
+      */
+      af::shared<int> col = result["id"];
+      std::set<int> new_ids(col.begin(), col.end());
+      typedef typename T::experiment_map_type::iterator iterator;
+      for (std::set<int>::iterator i = new_ids.begin(); i != new_ids.end(); ++i) {
+        iterator found = self.experiment_identifiers()->find(*i);
+        if (found != self.experiment_identifiers()->end()) {
+          (*result.experiment_identifiers())[found->first] = found->second;
+        }
+      }
+    }
     return result;
   }
 

tests/array_family/test_reflection_table.py

@@ -172,6 +172,17 @@ def test_delete():
     assert table.ncols() == 2
 
 
+def test_slice():
+    table = flex.reflection_table()
+    table["col1"] = flex.int([0, 0, 1, 2, 3, 4, 5])
+    table["id"] = flex.int([-1, 0, 1, 2, 3, 4, 5])
+    for i in range(0, 6):
+        table.experiment_identifiers()[i] = str(i)
+    sliced = table[4:]
+    assert sliced.nrows() == 3
+    assert dict(sliced.experiment_identifiers()) == {3: "3", 4: "4", 5: "5"}
+
+
 def test_row_operations():
     # The columns as lists
     c1 = list(range(10))