Modify compare() docstring, error-check, pass var_name.

.pylintrc

@@ -244,6 +244,7 @@ function-naming-style=snake_case
 
 # Good variable names which should always be accepted, separated by a comma
 good-names=b,
+           e,
            i,
            j,
            k,
@@ -265,7 +266,7 @@ good-names=b,
            ok,
            sd,
            tr,
-	         eta,
+           eta,
            Run,
            _log,
            _

CHANGELOG.md

@@ -10,6 +10,7 @@
 * Added interactive legend to bokeh `forestplot` ([1591](https://github.com/arviz-devs/arviz/pull/1591))
 * Added interactive legend to bokeh `ppcplot` ([1602](https://github.com/arviz-devs/arviz/pull/1602))
 * Added `data.log_likelihood`, `stats.ic_compare_method` and `plot.density_kind` to `rcParams` ([1611](https://github.com/arviz-devs/arviz/pull/1611))
+* Improve error messages in `stats.compare()`, and `var_name` parameter. ([1616](https://github.com/arviz-devs/arviz/pull/1616))
 
 ### Maintenance and fixes
 * Enforced using coordinate values as default labels ([1201](https://github.com/arviz-devs/arviz/pull/1201))

arviz/data/io_pymc3.py

@@ -89,7 +89,8 @@ def __init__(
         # this permits us to get the model from command-line argument or from with model:
         try:
             self.model = self.pymc3.modelcontext(model or self.model)
-        except TypeError:
+        except TypeError as e:
+            _log.error("Got error %s trying to find log_likelihood in translation.", e)
             self.model = None
 
         if self.model is None:
@@ -251,12 +252,17 @@ def _extract_log_likelihood(self, trace):
                 "`pip install pymc3>=3.8` or `conda install -c conda-forge pymc3>=3.8`."
             ) from err
         for var, log_like_fun in cached:
-            for k, chain in enumerate(trace.chains):
-                log_like_chain = [
-                    self.log_likelihood_vals_point(point, var, log_like_fun)
-                    for point in trace.points([chain])
-                ]
-                log_likelihood_dict.insert(var.name, np.stack(log_like_chain), k)
+            try:
+                for k, chain in enumerate(trace.chains):
+                    log_like_chain = [
+                        self.log_likelihood_vals_point(point, var, log_like_fun)
+                        for point in trace.points([chain])
+                    ]
+                    log_likelihood_dict.insert(var.name, np.stack(log_like_chain), k)
+            except TypeError as e:
+                raise TypeError(
+                    *tuple(["While computing log-likelihood for {var}: "] + list(e.args))
+                ) from e
         return log_likelihood_dict.trace_dict
 
     @requires("trace")

arviz/rcparams.py

@@ -9,11 +9,22 @@
 from collections.abc import MutableMapping
 from pathlib import Path
 from typing import Any, Dict
+from typing_extensions import Literal
+
+NO_GET_ARGS: bool = False
+try:
+    from typing_extensions import get_args
+except ImportError:
+    NO_GET_ARGS = True
+
 
 import numpy as np
 
 _log = logging.getLogger(__name__)
 
+ScaleKeyword = Literal["log", "negative_log", "deviance"]
+ICKeyword = Literal["loo", "waic"]
+
 
 def _make_validate_choice(accepted_values, allow_none=False, typeof=str):
     """Validate value is in accepted_values.
@@ -277,9 +288,17 @@ def validate_iterable(value):
     "plot.matplotlib.constrained_layout": (True, _validate_boolean),
     "plot.matplotlib.show": (False, _validate_boolean),
     "stats.hdi_prob": (0.94, _validate_probability),
-    "stats.information_criterion": ("loo", _make_validate_choice({"waic", "loo"})),
+    "stats.information_criterion": (
+        "loo",
+        _make_validate_choice({"loo", "waic"} if NO_GET_ARGS else set(get_args(ICKeyword))),
+    ),
     "stats.ic_pointwise": (False, _validate_boolean),
-    "stats.ic_scale": ("log", _make_validate_choice({"deviance", "log", "negative_log"})),
+    "stats.ic_scale": (
+        "log",
+        _make_validate_choice(
+            {"log", "negative_log", "deviance"} if NO_GET_ARGS else set(get_args(ScaleKeyword))
+        ),
+    ),
     "stats.ic_compare_method": (
         "stacking",
         _make_validate_choice({"stacking", "bb-pseudo-bma", "pseudo-bma"}),

arviz/stats/stats.py

@@ -2,17 +2,24 @@
 """Statistical functions in ArviZ."""
 import warnings
 from copy import deepcopy
-from typing import TYPE_CHECKING, List, Optional, Tuple, Union
+from typing import List, Optional, Tuple, Union, Mapping, cast, Callable
 
 import numpy as np
 import pandas as pd
 import scipy.stats as st
 import xarray as xr
 from scipy.optimize import minimize
+from typing_extensions import Literal
+
+NO_GET_ARGS: bool = False
+try:
+    from typing_extensions import get_args
+except ImportError:
+    NO_GET_ARGS = True
 
 from arviz import _log
 from ..data import InferenceData, convert_to_dataset, convert_to_inference_data
-from ..rcparams import rcParams
+from ..rcparams import rcParams, ScaleKeyword, ICKeyword
 from ..utils import Numba, _numba_var, _var_names, get_coords
 from .density_utils import get_bins as _get_bins
 from .density_utils import histogram as _histogram
@@ -27,9 +34,6 @@
 from ..sel_utils import xarray_var_iter
 from ..labels import BaseLabeller
 
-if TYPE_CHECKING:
-    from typing_extensions import Literal
-
 
 __all__ = [
     "apply_test_function",
@@ -45,7 +49,14 @@
 
 
 def compare(
-    dataset_dict, ic=None, method="stacking", b_samples=1000, alpha=1, seed=None, scale=None
+    dataset_dict: Mapping[str, InferenceData],
+    ic: Optional[ICKeyword] = None,
+    method: Literal["stacking", "BB-pseudo-BMA", "pseudo-MA"] = "stacking",
+    b_samples: int = 1000,
+    alpha: float = 1,
+    seed=None,
+    scale: Optional[ScaleKeyword] = None,
+    var_name: Optional[str] = None,
 ):
     r"""Compare models based on PSIS-LOO `loo` or WAIC `waic` cross-validation.
 
@@ -58,10 +69,10 @@ def compare(
     ----------
     dataset_dict: dict[str] -> InferenceData
         A dictionary of model names and InferenceData objects
-    ic: str
+    ic: str, optional
         Information Criterion (PSIS-LOO `loo` or WAIC `waic`) used to compare models. Defaults to
         ``rcParams["stats.information_criterion"]``.
-    method: str
+    method: str, optional
         Method used to estimate the weights for each model. Available options are:
 
         - 'stacking' : stacking of predictive distributions.
@@ -71,19 +82,19 @@ def compare(
           weighting, without Bootstrap stabilization (not recommended).
 
         For more information read https://arxiv.org/abs/1704.02030
-        Defaults to ``rcParams["stats.ic_compare_method"]``.
-    b_samples: int
+    b_samples: int, optional default = 1000
         Number of samples taken by the Bayesian bootstrap estimation.
         Only useful when method = 'BB-pseudo-BMA'.
-    alpha: float
+        Defaults to ``rcParams["stats.ic_compare_method"]``.
+    alpha: float, optional
         The shape parameter in the Dirichlet distribution used for the Bayesian bootstrap. Only
         useful when method = 'BB-pseudo-BMA'. When alpha=1 (default), the distribution is uniform
         on the simplex. A smaller alpha will keeps the final weights more away from 0 and 1.
-    seed: int or np.random.RandomState instance
+    seed: int or np.random.RandomState instance, optional
         If int or RandomState, use it for seeding Bayesian bootstrap. Only
         useful when method = 'BB-pseudo-BMA'. Default None the global
         np.random state is used.
-    scale: str
+    scale: str, optional
         Output scale for IC. Available options are:
 
         - `log` : (default) log-score (after Vehtari et al. (2017))
@@ -92,6 +103,9 @@ def compare(
 
         A higher log-score (or a lower deviance) indicates a model with better predictive
         accuracy.
+    var_name: str, optional
+        If there is more than a single observed variable in the ``InferenceData``, which
+        should be used as the basis for comparison.
 
     Returns
     -------
@@ -142,10 +156,16 @@ def compare(
     --------
     loo : Compute the Pareto Smoothed importance sampling Leave One Out cross-validation.
     waic : Compute the widely applicable information criterion.
-
     """
     names = list(dataset_dict.keys())
-    scale = rcParams["stats.ic_scale"] if scale is None else scale.lower()
+    if scale is not None:
+        scale = cast(ScaleKeyword, scale.lower())
+    else:
+        scale = cast(ScaleKeyword, rcParams["stats.ic_scale"])
+    allowable = ["log", "negative_log", "deviance"] if NO_GET_ARGS else get_args(ScaleKeyword)
+    if scale not in allowable:
+        raise ValueError(f"{scale} is not a valid value for scale: must be in {allowable}")
+
     if scale == "log":
         scale_value = 1
         ascending = False
@@ -156,9 +176,15 @@ def compare(
             scale_value = -2
         ascending = True
 
-    ic = rcParams["stats.information_criterion"] if ic is None else ic.lower()
+    if ic is None:
+        ic = cast(ICKeyword, rcParams["stats.information_criterion"])
+    else:
+        ic = cast(ICKeyword, ic.lower())
+    allowable = ["loo", "waic"] if NO_GET_ARGS else get_args(ICKeyword)
+    if ic not in allowable:
+        raise ValueError(f"{ic} is not a valid value for ic: must be in {allowable}")
     if ic == "loo":
-        ic_func = loo
+        ic_func: Callable = loo
         df_comp = pd.DataFrame(
             index=names,
             columns=[
@@ -172,7 +198,7 @@ def compare(
                 "warning",
                 "loo_scale",
             ],
-            dtype=np.float,
+            dtype=np.float_,
         )
         scale_col = "loo_scale"
     elif ic == "waic":
@@ -190,7 +216,7 @@ def compare(
                 "warning",
                 "waic_scale",
             ],
-            dtype=np.float,
+            dtype=np.float_,
         )
         scale_col = "waic_scale"
     else:
@@ -208,7 +234,12 @@ def compare(
     names = []
     for name, dataset in dataset_dict.items():
         names.append(name)
-        ics = ics.append([ic_func(dataset, pointwise=True, scale=scale)])
+        try:
+            # Here is where the IC function is actually computed -- the rest of this
+            # function is argument processing and return value formatting
+            ics = ics.append([ic_func(dataset, pointwise=True, scale=scale, var_name=var_name)])
+        except Exception as e:
+            raise e.__class__(f"Encountered error trying to compute {ic} from model {name}.") from e
     ics.index = names
     ics.sort_values(by=ic, inplace=True, ascending=ascending)
     ics[ic_i] = ics[ic_i].apply(lambda x: x.values.flatten())
@@ -1280,7 +1311,9 @@ def summary(
     n_vars = np.sum([joined[var].size // n_metrics for var in joined.data_vars])
 
     if fmt.lower() == "wide":
-        summary_df = pd.DataFrame(np.full((n_vars, n_metrics), np.nan), columns=metric_names)
+        summary_df = pd.DataFrame(
+            (np.full(cast(Tuple[int, int], (n_vars, n_metrics)), np.nan)), columns=metric_names
+        )
         indexs = []
         for i, (var_name, sel, isel, values) in enumerate(
             xarray_var_iter(joined, skip_dims={"metric"})

arviz/tests/base_tests/test_stats.py

@@ -40,6 +40,23 @@ def non_centered_eight():
     return non_centered_eight
 
 
+@pytest.fixture
+def multivariable_log_likelihood(centered_eight):
+    centered_eight = centered_eight.copy()
+    centered_eight.add_groups({"log_likelihood": centered_eight.sample_stats.log_likelihood})
+    centered_eight.log_likelihood = centered_eight.log_likelihood.rename_vars(
+        {"log_likelihood": "obs"}
+    )
+    new_arr = DataArray(
+        np.zeros(centered_eight.log_likelihood["obs"].values.shape),
+        dims=["chain", "draw", "school"],
+        coords=centered_eight.log_likelihood.coords,
+    )
+    centered_eight.log_likelihood["decoy"] = new_arr
+    delattr(centered_eight, "sample_stats")
+    return centered_eight
+
+
 def test_hdp():
     normal_sample = np.random.randn(5000000)
     interval = hdi(normal_sample)
@@ -151,7 +168,7 @@ def test_compare_same(centered_eight, multidim_models, method, multidim):
 
 def test_compare_unknown_ic_and_method(centered_eight, non_centered_eight):
     model_dict = {"centered": centered_eight, "non_centered": non_centered_eight}
-    with pytest.raises(NotImplementedError):
+    with pytest.raises(ValueError):
         compare(model_dict, ic="Unknown", method="stacking")
     with pytest.raises(ValueError):
         compare(model_dict, ic="loo", method="Unknown")
@@ -192,6 +209,20 @@ def test_compare_different_size(centered_eight, non_centered_eight):
         compare(model_dict, ic="waic", method="stacking")
 
 
+@pytest.mark.parametrize("ic", ["loo", "waic"])
+def test_compare_multiple_obs(multivariable_log_likelihood, centered_eight, non_centered_eight, ic):
+    compare_dict = {
+        "centered_eight": centered_eight,
+        "non_centered_eight": non_centered_eight,
+        "problematic": multivariable_log_likelihood,
+    }
+    with pytest.raises(TypeError, match="several log likelihood arrays"):
+        get_log_likelihood(compare_dict["problematic"])
+    with pytest.raises(TypeError, match="model problematic"):
+        compare(compare_dict, ic=ic)
+    assert compare(compare_dict, ic=ic, var_name="obs") is not None
+
+
 def test_summary_ndarray():
     array = np.random.randn(4, 100, 2)
     summary_df = summary(array)