fix stack plot bug part 1 issue 266 (#270)

RELEASE_NOTES.md

@@ -1,6 +1,7 @@
 
 # Next Release
 
+- [#270](https://github.com/IAMconsortium/pyam/pull/270) Include variables with zeros in `stack_plot`  (see [#266](https://github.com/IAMconsortium/pyam/issues/266))
 - [#269](https://github.com/IAMconsortium/pyam/pull/269) Ensure append doesn't accidentally swap indexes
 - [#268](https://github.com/IAMconsortium/pyam/pull/268) Update `aggregate_region` so it can find variables below sub-cateogories too
 - [#267](https://github.com/IAMconsortium/pyam/pull/267) Make clear error message if variable-region pair is missing when `check_aggregate_region` is called

pyam/plotting.py

@@ -472,7 +472,7 @@ def stack_plot(df, x='year', y='value', stack='variable',
     # is on the right (case of timeseries which go from negative to positive
     # is an edge case we haven't thought about as it's unlikely to apply to
     # us).
-    pos_cols = [c for c in _df if (_df[c] > 0).all()]
+    pos_cols = [c for c in _df if (_df[c] >= 0).all()]
     cross_cols = first_zero_times.columns[::-1].tolist()
     neg_cols = [c for c in _df if (_df[c] < 0).all()]
     col_order = pos_cols + cross_cols + neg_cols

tests/test_plotting.py

@@ -580,3 +580,21 @@ def test_stack_plot_negative_emissions_kwargs_custom_total(plot_stack_plot_df):
         ax=ax,
     )
     return fig
+
+
+@pytest.mark.mpl_image_compare(**MPL_KWARGS)
+def test_stack_plot_missing_zero_issue_266(plot_stack_plot_df):
+    df = pyam.IamDataFrame(pd.DataFrame(
+        [
+            ['a', 1, 2, 3, 4],
+            ['b', 0, 1, 2, 3],
+            ['c', -1, 1, -1, -1],
+            ['d', 1, 1, 1, -1]
+        ],
+        columns=['variable', 2010, 2020, 2030, 2040],
+    ), model='model_a', scenario='scen_a', region='World', unit='some_unit')
+
+    fig, ax = plt.subplots(figsize=(8, 8))
+    df.stack_plot(ax=ax)
+
+    return fig