Add __setitem__ to tables.

c/CHANGELOG.rst

@@ -1,7 +1,15 @@
 ----------------------
-[0.99.13] - 2021-07-08
+[0.99.14] - 2021-0X-XX
 ----------------------
 
+**Features**
+
+- Add `tsk_X_table_update_row` methods which allow modifying single rows of tables
+  (:user:`jeromekelleher`, :issue:`1545`, :pr:`1552`).
+
+----------------------
+[0.99.13] - 2021-07-08
+----------------------
 **Fixes**
 
 - Fix segfault when very large columns overflow 

python/CHANGELOG.rst

@@ -1,3 +1,13 @@
+--------------------
+[0.3.8] - 2021-0X-XX
+--------------------
+
+**Features**
+
+- Add `__setitem__` to all tables allowing single rows to be updated. For example
+  `tables.nodes[0] = tables.nodes[0].replace(flags=tskit.NODE_IS_SAMPLE)`
+  (:user:`jeromekelleher`, :user:`benjeffery`, :issue:`1545`, :pr:`1600`).
+
 --------------------
 [0.3.7] - 2021-07-08
 --------------------

python/tests/test_tables.py

@@ -448,6 +448,64 @@ class NotADuck:
         with pytest.raises(AttributeError, match="'NotADuck' object has no attribute"):
             self.table_class().append(NotADuck())
 
+    def test_setitem(self):
+        table = self.table_class()
+        for row in self.make_transposed_input_data(10):
+            table.append(table.row_class(**row))
+        table2 = self.table_class()
+        for row in self.make_transposed_input_data(20)[10:]:
+            table2.append(table.row_class(**row))
+        assert table != table2
+
+        copy = table.copy()
+        for j in range(10):
+            table[j] = table[j]
+        table.assert_equals(copy)
+
+        for j in range(10):
+            table[j] = table2[j]
+        table.assert_equals(table2)
+
+    def test_setitem_duck_type(self):
+        class Duck:
+            pass
+
+        table = self.table_class()
+        for row in self.make_transposed_input_data(10):
+            table.append(table.row_class(**row))
+        table2 = self.table_class()
+        for row in self.make_transposed_input_data(20)[10:]:
+            table2.append(table.row_class(**row))
+        assert table != table2
+
+        for j in range(10):
+            duck = Duck()
+            for k, v in dataclasses.asdict(table2[j]).items():
+                setattr(duck, k, v)
+            table[j] = duck
+        table.assert_equals(table2)
+
+    def test_setitem_error(self):
+        class NotADuck:
+            pass
+
+        table = self.table_class()
+        table.append(table.row_class(**self.make_transposed_input_data(1)[0]))
+        with pytest.raises(AttributeError, match="'NotADuck' object has no attribute"):
+            table[0] = NotADuck()
+
+        with pytest.raises(IndexError, match="Index out of bounds"):
+            self.table_class()[0] = table[0]
+        with pytest.raises(IndexError, match="Index out of bounds"):
+            self.table_class()[-1] = table[0]
+
+        with pytest.raises(TypeError, match="Index must be integer"):
+            self.table_class()[0.5] = table[0]
+        with pytest.raises(TypeError, match="Index must be integer"):
+            self.table_class()[None] = table[0]
+        with pytest.raises(TypeError, match="Index must be integer"):
+            self.table_class()[[1]] = table[0]
+
     def test_set_columns_data(self):
         for num_rows in [0, 10, 100, 1000]:
             input_data = {col.name: col.get_input(num_rows) for col in self.columns}
@@ -1347,12 +1405,6 @@ def test_bad_indexes(self, table):
         with pytest.raises(TypeError, match="not supported between instances"):
             table["foobar"]
 
-    def test_not_writable(self, table):
-        with pytest.raises(TypeError, match="object does not support item assignment"):
-            table[5] = 5
-        with pytest.raises(TypeError, match="object does not support item assignment"):
-            table[[5]] = 5
-
 
 common_tests = [
     CommonTestsMixin,
@@ -4665,3 +4717,14 @@ def test_with_mutation_times(self):
         tables.compute_mutation_times()
         ts = tables.tree_sequence()
         self.verify_subset_union(ts)
+
+
+class TestTableSetitemMetadata:
+    @pytest.mark.parametrize("table_name", tskit.TABLE_NAMES)
+    def test_setitem_metadata(self, ts_fixture, table_name):
+        table = getattr(ts_fixture.tables, table_name)
+        if hasattr(table, "metadata_schema"):
+            assert table.metadata_schema == tskit.MetadataSchema({"codec": "json"})
+            assert table[0].metadata != table[1].metadata
+            table[0] = table[1]
+            assert table[0] == table[1]

python/tskit/tables.py

@@ -344,7 +344,7 @@ def __getitem__(self, index):
         is True. Note that as the result is a new table, the row ids will change as tskit
         row ids are row indexes.
 
-        :param index: the zero-index of a desired row, a slice of the desired rows, an
+        :param index: the index of a desired row, a slice of the desired rows, an
             iterable or array of the desired row numbers, or a boolean array to use as
             a mask.
         """
@@ -374,6 +374,43 @@ def __getitem__(self, index):
 
         return ret
 
+    def __setitem__(self, index, new_row):
+        """
+        Replaces a row of this table at the specified index with information from a
+        row-like object. Metadata, will be validated and encoded according to the table's
+        :attr:`metadata_schema<tskit.IndividualTable.metadata_schema>`.
+
+        :param index: the index of the row to change
+        :param row-like new_row: An object that has attributes corresponding to the
+            properties of the new row. Both the objects returned from ``table[i]`` and
+            e.g. ``ts.individual(i)`` work for this purpose, along with any other
+            object with the correct attributes.
+        """
+        if isinstance(index, numbers.Integral):
+            # Single row by integer
+            if index < 0:
+                index += len(self)
+            if index < 0 or index >= len(self):
+                raise IndexError("Index out of bounds")
+        else:
+            raise TypeError("Index must be integer")
+
+        row_data = {
+            column: getattr(new_row, column)
+            for column in self.column_names
+            if "_offset" not in column
+        }
+
+        # Encode the metadata - note that if this becomes a perf bottleneck it is
+        # possible to use the cached, encoded metadata in the row object, rather than
+        # decode and reencode
+        if "metadata" in row_data:
+            row_data["metadata"] = self.metadata_schema.validate_and_encode_row(
+                row_data["metadata"]
+            )
+
+        self.ll_table.update_row(row_index=index, **row_data)
+
     def append(self, row):
         """
         Adds a new row to this table and returns the ID of the new row. Metadata, if