plot_elpd, avoid modyfing the input dict (#1477)

* avoid modyfing the input dict

* update changelog

CHANGELOG.md

@@ -30,7 +30,7 @@
 * Automatically get the current axes instance for `plt_kde`, `plot_dist` and `plot_hdi` ([1452](https://github.com/arviz-devs/arviz/pull/1452))
 * Add grid argument to manually specify the number of rows and columns ([1459](https://github.com/arviz-devs/arviz/pull/1459))
 * Switch to `compact=True` by default in our plots ([1468](https://github.com/arviz-devs/arviz/issues/1468))
-
+* `plot_elpd`, avoid modifying the input dict ([1477](https://github.com/arviz-devs/arviz/issues/1477))
 
 ### Deprecation
 

arviz/plots/elpdplot.py

@@ -1,4 +1,5 @@
 """Plot pointwise elpd estimations of inference data."""
+from copy import deepcopy
 import numpy as np
 
 from ..data import convert_to_inference_data
@@ -115,6 +116,7 @@ def plot_elpd(
     ic_fun = loo if ic == "loo" else waic
 
     # Make sure all object are ELPDData
+    compare_dict = deepcopy(compare_dict)
     for k, item in compare_dict.items():
         if not isinstance(item, ELPDData):
             compare_dict[k] = ic_fun(convert_to_inference_data(item), pointwise=True, scale=scale)