plot_hdi raise exception when x is string (#2412) (#2413)

* plot_hdi - add exception if x is string type

* add test that plot_hdi raises when x is string

* run black

* update changelog

* Change TypeError to NotImplementedError, modify error message

* Fix typo in error message

* remove backticks from error message

* escape special characters in pytest.raise

* pylint and black

* run isort

Author: milesalanmoore

CHANGELOG.md

@@ -9,6 +9,7 @@
 - Only emit a warning for custom groups in `InferenceData` when explicitly requested ([2401](https://github.com/arviz-devs/arviz/pull/2401))
 - Splits Bayes Factor computation out from `az.plot_bf` into `az.bayes_factor` ([2402](https://github.com/arviz-devs/arviz/issues/2402))
 - Update `method="sd"` of `mcse` to not use normality assumption ([2167](https://github.com/arviz-devs/arviz/pull/2167)) 
+- Add exception in `az.plot_hdi` for `x` of type `str` ([2413](https://github.com/arviz-devs/arviz/pull/2413))
 
 ### Documentation
 - Add example of ECDF comparison plot to gallery ([2178](https://github.com/arviz-devs/arviz/pull/2178))

arviz/plots/hdiplot.py

@@ -136,6 +136,11 @@ def plot_hdi(
     x = np.asarray(x)
     x_shape = x.shape
 
+    if isinstance(x[0], str):
+        raise NotImplementedError(
+            "The `arviz.plot_hdi()` function does not support categorical data. "
+            "Consider using `arviz.plot_forest()`."
+        )
     if y is None and hdi_data is None:
         raise ValueError("One of {y, hdi_data} is required")
     if hdi_data is not None and y is not None:

arviz/tests/base_tests/test_plots_matplotlib.py

@@ -2,21 +2,22 @@
 
 # pylint: disable=redefined-outer-name,too-many-lines
 import os
+import re
 from copy import deepcopy
 
 import matplotlib.pyplot as plt
 import numpy as np
 import pytest
+import xarray as xr
 from matplotlib import animation
 from pandas import DataFrame
 from scipy.stats import gaussian_kde, norm
-import xarray as xr
 
 from ...data import from_dict, load_arviz_data
 from ...plots import (
     plot_autocorr,
-    plot_bpv,
     plot_bf,
+    plot_bpv,
     plot_compare,
     plot_density,
     plot_dist,
@@ -43,20 +44,20 @@
     plot_ts,
     plot_violin,
 )
+from ...plots.dotplot import wilkinson_algorithm
+from ...plots.plot_utils import plot_point_interval
 from ...rcparams import rc_context, rcParams
 from ...stats import compare, hdi, loo, waic
 from ...stats.density_utils import kde as _kde
-from ...utils import _cov, BehaviourChangeWarning
-from ...plots.plot_utils import plot_point_interval
-from ...plots.dotplot import wilkinson_algorithm
+from ...utils import BehaviourChangeWarning, _cov
 from ..helpers import (  # pylint: disable=unused-import
+    RandomVariableTestClass,
     create_model,
     create_multidimensional_model,
     does_not_warn,
     eight_schools_params,
     models,
     multidim_models,
-    RandomVariableTestClass,
 )
 
 rcParams["data.load"] = "eager"
@@ -1236,6 +1237,23 @@ def test_plot_hdi_dataset_error(models):
         plot_hdi(np.arange(8), hdi_data=hdi_data)
 
 
+def test_plot_hdi_string_error():
+    """Check x as type string raises an error."""
+    x_data = ["a", "b", "c", "d"]
+    y_data = np.random.normal(0, 5, (1, 200, len(x_data)))
+    hdi_data = hdi(y_data)
+    with pytest.raises(
+        NotImplementedError,
+        match=re.escape(
+            (
+                "The `arviz.plot_hdi()` function does not support categorical data. "
+                "Consider using `arviz.plot_forest()`."
+            )
+        ),
+    ):
+        plot_hdi(x=x_data, y=y_data, hdi_data=hdi_data)
+
+
 def test_plot_hdi_datetime_error():
     """Check x as datetime raises an error."""
     x_data = np.arange(start="2022-01-01", stop="2022-03-01", dtype=np.datetime64)