Documentation: Added documentation for custom columns

docs/dfanalyzer_custom_columns.rst

@@ -0,0 +1,41 @@
+===========================================
+Custom Columns Derived from DFTracer
+===========================================
+
+This section describes how to derive custom columns for a DFAnalyzer data framework from DFTracer events using a custom function and load specific fields.
+
+Example: Custom Workflow Columns
+================================
+
+We can define custom columns in `DFAnalyzer` by specifying a function that extracts the desired fields from the `json_object` and then loading those fields with their corresponding types.
+
+Below is an example of how to define a custom function to derive columns from a Pegasus Montage workflow trace:
+
+.. code-block:: python
+
+    def wf_cols_function(json_object, current_dict, time_approximate, condition_fn, load_data):
+        d = {}
+        if "args" in json_object:
+            if "size" in json_object["args"]:
+                d["size"] = int(json_object["args"]["size"])
+            if "ret" in json_object["args"]:
+                d["ret"] = int(json_object["args"]["ret"])
+        return d
+
+    load_cols_wf = {'size': "int64[pyarrow]", 'ret': "int64[pyarrow]"}
+
+Next, use this function in `DFAnalyzer` to load traces with the custom columns (here is an example of loading Montage traces):
+
+.. code-block:: python
+
+    from dfanalyzer import DFAnalyzer
+
+    analyzer = DFAnalyzer(
+        "/path/to/montage-*-preload.pfw.gz", 
+        load_fn=wf_cols_function, 
+        load_cols=load_cols_wf
+    )
+
+Here, the custom columns `size`, `ret`, and `cmd` are loaded into the `DFAnalyzer` using the `wf_cols_function`.
+
+You can modify the function and column types to match the fields relevant to your workload.

docs/index.rst

@@ -28,6 +28,7 @@ DFTracer: is a library for profiling I/O calls and application functions.
    dfanalyzer_conf
    dfanalyzer_alcf_polaris
    dfanalyzer_overlap_analysis
+   dfanalyzer_custom_columns  
 
 .. toctree::
    :maxdepth: 2