add readme

Signed-off-by: Sidhant Kohli <[email protected]>

README.md

@@ -47,6 +47,7 @@ pre-commit install
     - [Map](https://github.com/numaproj/numaflow-python/tree/main/examples/map)
     - [Reduce](https://github.com/numaproj/numaflow-python/tree/main/examples/reduce)
     - [Map Stream](https://github.com/numaproj/numaflow-python/tree/main/examples/mapstream)
+    - [Batch Map](https://github.com/numaproj/numaflow-python/tree/main/examples/batchmap)
 - [Implement User Defined Sinks](https://github.com/numaproj/numaflow-python/tree/main/examples/sink)
 - [Implement User Defined SideInputs](https://github.com/numaproj/numaflow-python/tree/main/examples/sideinput)
 
@@ -111,6 +112,8 @@ These are the class names for the server types supported by each of the function
         - ReduceAsyncServer
     - MapStream
         - MapStreamAsyncServer
+    - BatchMap
+      - BatchMapAsyncServer
     - Source Transform
         - SourceTransformServer
         - SourceTransformMultiProcServer
@@ -147,6 +150,8 @@ The list of base handler classes for each of the functionalities is given below
         - MapStreamer
     - Source Transform
         - SourceTransformer
+    - Batch Map
+      - BatchMapper
 - UDSource
     - Sourcer
 - UDSink

examples/batchmap/README.md

@@ -0,0 +1,66 @@
+## BatchMap Interface
+The BatchMap interface allows developers to 
+process multiple data items together in a single UDF handler.
+
+
+### What is BatchMap?
+BatchMap is an interface that allows developers to process multiple data items 
+in a UDF single call, rather than each item in separate calls. 
+
+
+The BatchMap interface can be helpful in scenarios 
+where performing operations on a group of data can be more efficient.
+
+
+### Understanding the User Interface
+The BatchMap interface requires developers to implement a handler with a specific signature.
+Here is the signature of the BatchMap handler:
+
+```python
+async def handler(datums: AsyncIterable[Datum]) -> BatchResponses:
+```
+The handler takes an iterable of `Datum` objects and returns
+`BatchResponses`. 
+The `BatchResponses` object is a list of the *same length* as the input
+datums, with each item corresponding to the response for one request datum.
+
+To clarify, let's say we have three data items:
+
+```json lines
+data_1 = {"name": "John", "age": 25}
+data_2 = {"name": "Jane", "age": 30}
+data_3 = {"name": "Bob", "age": 45}
+```
+
+These data items will be grouped together by numaflow and
+passed to the handler as an iterable:
+
+```python
+result = await handler([data_1, data_2, data_3])
+```
+
+The result will be a BatchResponses object, which is a list of responses corresponding to each input data item's processing. 
+
+### Important Considerations
+When using BatchMap, there are a few important considerations to keep in mind:
+
+- Ensure that the `BatchResponses` object is tagged with the *correct request ID*. 
+Each Datum has a unique ID tag, which will be used by Numaflow to ensure correctness.
+
+```python
+async for datum in datums:
+    batch_response = BatchResponse.new_batch_response(datum.id)
+```
+
+
+- Ensure that the length of the `BatchResponses`
+list is equal to the number of requests received. 
+**This means that for every input data item**, there should be a corresponding 
+response in the BatchResponses list.
+
+Use batch processing only when it makes sense. In some 
+scenarios, batch processing may not be the most 
+efficient approach, and processing data items one by one 
+could be a better option.
+The burden of concurrent processing of the data will rely on the 
+UDF implementation in this use case.