doc(map): call out unary, batch, and streaming (#3164)

Signed-off-by: Vigith Maurice <vigith@gmail.com>

Author: vigith

docs/user-guide/user-defined-functions/map/map.md

@@ -2,16 +2,6 @@
 
 Map in a Map vertex takes an input and returns 0, 1, or more outputs (also known as flat-map operation). Map is an element wise operator.
 
-## Build Your Own UDF
-
-You can build your own UDF in multiple languages.
-
-Check the links below to see the UDF examples for different languages.
-
-- [Python](https://github.com/numaproj/numaflow-python/tree/main/packages/pynumaflow/examples/map/)
-- [Golang](https://github.com/numaproj/numaflow-go/tree/main/examples/mapper/)
-- [Java](https://github.com/numaproj/numaflow-java/tree/main/examples/src/main/java/io/numaproj/numaflow/examples/map/)
-
 After building a docker image for the written UDF, specify the image as below in the vertex spec.
 
 ```yaml
@@ -23,44 +13,45 @@ spec:
           image: my-python-udf-example:latest
 ```
 
-### Streaming Mode
+Map supports three modes: [Unary](#unary-mode), [Streaming](#streaming-mode), and [Batch](#batch-mode).
 
-In cases the map function generates more than one output (e.g., flat map), the UDF can be
-configured to run in a streaming mode instead of batching, which is the default mode.
-In streaming mode, the messages will be pushed to the downstream vertices once generated
-instead of in a batch at the end.
+## Unary Mode
 
-Note that to maintain data orderliness, we restrict the read batch size to be `1`.
+Unary Map is the default mode where each input message is processed individually and returns 0, 1, or more outputs.
 
-```yaml
-spec:
-  vertices:
-    - name: my-vertex
-      limits:
-        # mapstreaming won't work if readBatchSize is != 1      
-        readBatchSize: 1
-```
+Check the links below to see the UDF examples for different languages.
+
+- [Python](https://github.com/numaproj/numaflow-python/tree/main/packages/pynumaflow/examples/map/)
+- [Golang](https://github.com/numaproj/numaflow-go/tree/main/examples/mapper/)
+- [Java](https://github.com/numaproj/numaflow-java/tree/main/examples/src/main/java/io/numaproj/numaflow/examples/map/)
+
+## Streaming Mode
+
+In cases the map function generates more than one output (e.g., flat map), the UDF can be
+configured to run in a streaming mode where the messages will be pushed to the downstream vertices as 
+soon as the output is generated instead of collecting all the responses and then sending them 
+together at the end when the function returns.
 
 Check the links below to see the UDF examples in streaming mode for different languages.
 
 - [Python](https://github.com/numaproj/numaflow-python/tree/main/packages/pynumaflow/examples/mapstream/flatmap_stream/)
 - [Golang](https://github.com/numaproj/numaflow-go/tree/main/examples/mapstreamer/flatmap_stream/)
 - [Java](https://github.com/numaproj/numaflow-java/tree/main/examples/src/main/java/io/numaproj/numaflow/examples/mapstream/flatmapstream/)
 
-### Batch Map Mode
+## Batch Mode
 
 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.
 
-#### Important Considerations
+### 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. 
+- 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.
-- Ensure that the length of the BatchResponses list is equal to the number of requests received. This means that for 
+- 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.
 - The total batch size can be up to `readBatchSize` long.
 
@@ -71,7 +62,7 @@ Check the links below to see the UDF examples in batch mode for different langua
 - [Java](https://github.com/numaproj/numaflow-java/tree/main/examples/src/main/java/io/numaproj/numaflow/examples/batchmap/)
 - [Rust](https://github.com/numaproj/numaflow-rs/tree/main/examples/batchmap-cat/)
 
-### Available Environment Variables
+## Available Environment Variables
 
 Some environment variables are available in the user-defined function container, they might be useful in your own UDF implementation.
 
@@ -81,7 +72,9 @@ Some environment variables are available in the user-defined function container,
 - `NUMAFLOW_PIPELINE_NAME` - Name of the pipeline.
 - `NUMAFLOW_VERTEX_NAME` - Name of the vertex.
 
-### Configuration
+## Configuration
+
+To achieve ordering, please set `readBatchSize` to 1.
 
 Configuration data can be provided to the UDF container at runtime multiple ways.