Support freq="W" in standardized indices

CHANGELOG.rst

@@ -28,6 +28,7 @@ New features and enhancements
 * ``xclim.indices.run_length.runs_with_holes`` allows to input a condition that must be met for a run to start and a second condition that must be met for the run to stop. (:pull:`1778`).
 * New generic compute function ``xclim.indices.generic.thresholded_events`` that finds events based on a threshold condition and returns basic stats for each. See also ``xclim.indices.run_length.find_events``. (:pull:`1778`).
 * ``xclim.core.units.rate2amount`` and ``xclim.core.units.amount2rate`` can now also accept quantities (pint objects or strings), in which case the ``dim`` argument must be the ``time`` coordinate through which we can find the sampling rate. (:pull:`1778`).
+* `xclim.indices.stats.standardized_index` now supports a weekly resampling frequency. Only standard calendar is supported for this mode. (:issue:`1892`, :pull:`1952`)
 
 Bug fixes
 ^^^^^^^^^

xclim/indices/stats.py

@@ -657,6 +657,8 @@ def preprocess_standardized_index(
             group = "time.dayofyear"
         elif compare_offsets(final_freq, "==", "MS"):
             group = "time.month"
+        elif compare_offsets(final_freq, "==", "W"):
+            group = "time.week"
         else:
             raise ValueError(
                 f"The input (following resampling if applicable) has a frequency `{final_freq}` "
@@ -910,6 +912,9 @@ def reindex_time(da, da_ref, group):
         elif group == "time.month":
             da = da.rename(month="time").reindex(time=da_ref.time.dt.month)
             da["time"] = da_ref.time
+        elif group == "time.week":
+            da = da.rename(week="time").reindex(time=da_ref.time.dt.week)
+            da["time"] = da_ref.time
         # I don't think rechunking is necessary here, need to check
         return da if not uses_dask(da) else da.chunk({"time": -1})