fix bug when declaring a cmap and color argument would produce len(df…

RELEASE_NOTES.md

@@ -6,6 +6,7 @@
 - [#212](https://github.com/IAMconsortium/pyam/pull/212) Now natively support reading R-style data frames with year columns like "X2015"
 - [#202](https://github.com/IAMconsortium/pyam/pull/202) Extend the `df.rename()` function with a `check_duplicates (default True)` validation option
 - [#201](https://github.com/IAMconsortium/pyam/pull/201) Added native support for legends outside of plots with `pyam.plotting.OUTSIDE_LEGEND` with a tutorial
+- [#200](https://github.com/IAMconsortium/pyam/pull/200) Bugfix when providing `cmap`  and `color`  arguments to plotting functions
 - [#199](https://github.com/IAMconsortium/pyam/pull/199) Initializing an `IamDataFrame` accepts kwargs to fill or create from the data any missing required columns
 - [#197](https://github.com/IAMconsortium/pyam/pull/197) Added a `normalize` function that normalizes all data in a data frame to a specific time period.
 - [#195](https://github.com/IAMconsortium/pyam/pull/195) Fix filtering for `time`, `day` and `hour` to use generic `pattern_match()` (if such a column exists) in 'year'-formmatted IamDataFrames

pyam/plotting.py

@@ -32,7 +32,7 @@
 
 from pyam.logger import logger
 from pyam.run_control import run_control
-from pyam.utils import requires_package, SORT_IDX, isstr
+from pyam.utils import requires_package, IAMC_IDX, SORT_IDX, isstr
 
 from pandas.plotting._style import _get_standard_colors
 
@@ -108,9 +108,13 @@ def assign_style_props(df, color=None, marker=None, linestyle=None,
     df : pd.DataFrame
         data to be used for style properties
     """
+    if color is None and cmap is not None:
+        raise ValueError('`cmap` must be provided with the `color` argument')
+
     # determine color, marker, and linestyle for each line
-    defaults = default_props(reset=True, num_colors=len(df),
-                             colormap=cmap)
+    n = len(df[color].unique()) if color in df.columns else \
+        len(df[list(set(df.columns) & set(IAMC_IDX))].drop_duplicates())
+    defaults = default_props(reset=True, num_colors=n, colormap=cmap)
 
     props = {}
     rc = run_control()

tests/test_plotting.py

@@ -57,6 +57,22 @@ def test_line_plot(plot_df):
     return fig
 
 
+def test_line_plot_cmap(plot_df):
+    # need to provide cmap and color both
+    _plot_df = copy.deepcopy(plot_df)
+    _plot_df.set_meta(meta=[np.nan] * 4, name='test')
+    pytest.raises(ValueError, _plot_df.line_plot, cmap='magma')
+
+
+@pytest.mark.mpl_image_compare(**MPL_KWARGS)
+def test_line_plot_cmap_color_arg(plot_df):
+    _plot_df = copy.deepcopy(plot_df)
+    _plot_df.set_meta(meta=[np.nan] * 4, name='test')
+    fig, ax = plt.subplots(figsize=(8, 8))
+    _plot_df.line_plot(ax=ax, legend=True, cmap='magma', color='variable')
+    return fig
+
+
 @pytest.mark.mpl_image_compare(**MPL_KWARGS)
 def test_line_plot_dict_legend(plot_df):
     fig, ax = plt.subplots(figsize=(8, 8))