feat(transform): implement columns pivot map function

dlt/sources/helpers/transform.py

@@ -1,3 +1,5 @@
+from typing import List, Union
+
 from dlt.common.typing import TDataItem
 from dlt.extract.items import ItemTransformFunctionNoMeta
 
@@ -24,3 +26,31 @@ def _filter(_: TDataItem) -> bool:
         return count > max_items
 
     return _filter
+
+
+def pivot(columns: Union[str, List[str]], prefix: str) -> ItemTransformFunctionNoMeta[TDataItem]:
+    """Pivot a list of columns into a dictionary.
+
+    Args:
+        columns (Union[str, List[str]]): list of column names
+        prefix (str): prefix to add to the column names
+
+    Returns:
+        ItemTransformFunctionNoMeta[TDataItem]:
+            A function to pivot columns into a dict.
+    """
+    if isinstance(columns, str):
+        columns = [columns]
+
+    def _transformer(item: TDataItem) -> TDataItem:
+        """Pivot columns into a dictionary.
+
+        Args:
+            item (TDataItem): a data item.
+
+        Returns:
+            TDataItem: a data item with pivoted columns.
+        """
+        return {prefix + col: item[ind] for ind, col in enumerate(columns)}
+
+    return _transformer

tests/pipeline/test_pipeline_state.py

@@ -11,6 +11,7 @@
 from dlt.common import pipeline as state_module
 from dlt.common.utils import uniq_id
 from dlt.common.destination.reference import Destination
+from dlt.sources.helpers.transform import pivot
 
 from dlt.pipeline.exceptions import PipelineStateEngineNoUpgradePathException, PipelineStepFailed
 from dlt.pipeline.pipeline import Pipeline
@@ -486,6 +487,27 @@ def transform(item):
     )
 
 
+def test_transform_function_pivot() -> None:
+    @dlt.resource
+    def test_resource():
+        for row in (
+            [[1, 2, 3], [4, 5, 6]],
+            [[7, 8, 9], [10, 11, 12]],
+        ):
+            yield row
+
+    res = test_resource()
+    res.add_map(pivot(["a", "b", "c"], "prefix_"))
+
+    result = list(res)
+    assert result == [
+        {"prefix_a": 1, "prefix_b": 2, "prefix_c": 3},
+        {"prefix_a": 4, "prefix_b": 5, "prefix_c": 6},
+        {"prefix_a": 7, "prefix_b": 8, "prefix_c": 9},
+        {"prefix_a": 10, "prefix_b": 11, "prefix_c": 12},
+    ]
+
+
 def test_migrate_pipeline_state(test_storage: FileStorage) -> None:
     # test generation of version hash on migration to v3
     state_v1 = load_json_case("state/state.v1")