feat(SelectionsMixin): allow selection from index map values

draco/analysis/transform.py

@@ -1354,22 +1354,35 @@ def process(self, data: containers.ContainerBase) -> containers.ContainerBase:
             Container of same type as the input with specific axis selections.
             Any datasets not included in the selections will not be initialized.
         """
-        # Re-format selections to only use axis name
-        for ax_sel in list(self._sel):
-            ax = ax_sel.replace("_sel", "")
-            self._sel[ax] = self._sel.pop(ax_sel)
+        sel = {}
+
+        # Parse axes with selections and reformat to use only
+        # the axis name
+        for k in self.selections:
+            *axis, type_ = k.split("_")
+            axis_name = "_".join(axis)
+
+            ax_sel = self._sel.get(f"{axis_name}_sel")
+
+            if type_ == "map":
+                # Use index map to get the correct axis indices
+                imap = list(data.index_map[axis_name])
+                ax_sel = [imap.index(x) for x in ax_sel]
+
+            if ax_sel is not None:
+                sel[axis_name] = ax_sel
 
         # Figure out the axes for the new container and
         # Apply the downselections to each axis index_map
         output_axes = {
-            ax: mpiarray._apply_sel(data.index_map[ax], sel, 0)
-            for ax, sel in self._sel.items()
+            ax: mpiarray._apply_sel(data.index_map[ax], ax_sel, 0)
+            for ax, ax_sel in sel.items()
         }
         # Create the output container without initializing any datasets.
         out = data.__class__(
             axes_from=data, attrs_from=data, skip_datasets=True, **output_axes
         )
-        containers.copy_datasets_filter(data, out, selection=self._sel)
+        containers.copy_datasets_filter(data, out, selection=sel)
 
         return out
 

draco/core/io.py

@@ -26,6 +26,7 @@
 import os.path
 import shutil
 import subprocess
+from functools import partial
 from typing import ClassVar, Optional, Union
 
 import numpy as np
@@ -351,6 +352,11 @@ class SelectionsMixin:
     selections : dict, optional
         A dictionary of axis selections. See below for details.
 
+    allow_index_map : bool, optional
+        If true, selections can be made based on an index_map dataset.
+        This cannot be implemented when reading from disk. See below for
+        details. Default is False.
+
     Selections
     ----------
     Selections can be given to limit the data read to specified subsets. They can be
@@ -359,11 +365,13 @@ class SelectionsMixin:
     Selections can be given as a slice with an `<axis name>_range` key with either
     `[start, stop]` or `[start, stop, step]` as the value. Alternatively a list of
     explicit indices to extract can be given with the `<axis name>_index` key, and
-    the value is a list of the indices. If both `<axis name>_range` and `<axis
-    name>_index` keys are given the former will take precedence, but you should
-    clearly avoid doing this.
+    the value is a list of the indices. Finally, selection based on an `index_map`
+    can be given with specific `index_map` entries with the `<axis name>_map` key,
+    which will be converted to axis indices. `<axis name>_range` will take precedence
+    over `<axis name>_index`, which will in turn take precedence over `<axis_name>_map`,
+    but you should clearly avoid doing this.
 
-    Additionally index based selections currently don't work for distributed reads.
+    Additionally, index-based selections currently don't work for distributed reads.
 
     Here's an example in the YAML format that the pipeline uses:
 
@@ -373,9 +381,11 @@ class SelectionsMixin:
             freq_range: [256, 512, 4]  # A strided slice
             stack_index: [1, 2, 4, 9, 16, 25, 36, 49, 64]  # A sparse selection
             stack_range: [1, 14]  # Will override the selection above
+            pol_map: ["XX", "YY"] # Select the indices corresponding to these entries
     """
 
     selections = config.Property(proptype=dict, default=None)
+    allow_index_map = config.Property(proptype=bool, default=False)
 
     def setup(self):
         """Resolve the selections."""
@@ -386,7 +396,14 @@ def _resolve_sel(self):
 
         sel = {}
 
-        sel_parsers = {"range": self._parse_range, "index": self._parse_index}
+        sel_parsers = {
+            "range": self._parse_range,
+            "index": partial(self._parse_index, type_=int),
+            "map": self._parse_index,
+        }
+
+        if not self.allow_index_map:
+            del sel_parsers["map"]
 
         # To enforce the precedence of range vs index selections, we rely on the fact
         # that a sort will place the axis_range keys after axis_index keys
@@ -398,7 +415,8 @@ def _resolve_sel(self):
 
             if type_ not in sel_parsers:
                 raise ValueError(
-                    f'Unsupported selection type "{type_}", or invalid key "{k}"'
+                    f'Unsupported selection type "{type_}", or invalid key "{k}". '
+                    "Note that map-type selections require `allow_index_map=True`."
                 )
 
             sel[f"{axis_name}_sel"] = sel_parsers[type_](self.selections[k])
@@ -419,15 +437,15 @@ def _parse_range(self, x):
 
         return slice(*x)
 
-    def _parse_index(self, x):
+    def _parse_index(self, x, type_=object):
         # Parse and validate an index type selection
 
         if not isinstance(x, (list, tuple)) or len(x) == 0:
             raise ValueError(f"Index spec must be a non-empty list or tuple. Got {x}.")
 
         for v in x:
-            if not isinstance(v, int):
-                raise ValueError(f"All elements of index spec must be ints. Got {x}")
+            if not isinstance(v, type_):
+                raise ValueError(f"All elements of index spec must be {type_}. Got {x}")
 
         return list(x)