Add just parameter to geom_bar and geom_col

Author: has2k1

doc/changelog.qmd

@@ -68,6 +68,9 @@ title: Changelog
   )
   ```
 
+- Geoms [](:class:`~plotnine.geom_bar`) and [](:class:`~plotnine.geom_col`) have
+  gained new parameter `just` that controls how the bars align with the axis break point.
+
 ### Enhancements
 
 - Included datasets [](:attr:`~plotnine.data.mpg`), [](:attr:`~plotnine.data.msleep`) and

plotnine/geoms/geom_bar.py

@@ -20,6 +20,11 @@ class geom_bar(geom_rect):
     Parameters
     ----------
     {common_parameters}
+    just : float, default=0.5
+        How to align the column with respect to the axis breaks. The default
+        `0.5` aligns the center of the column with the break. `0` aligns the
+        left of the of the column with the break and `1` aligns the right of
+        the column with the break.
     width : float, default=None
         Bar width. If `None`{.py}, the width is set to
         `90%` of the resolution of the data.
@@ -35,6 +40,7 @@ class geom_bar(geom_rect):
         "stat": "count",
         "position": "stack",
         "na_rm": False,
+        "just": 0.5,
         "width": None,
     }
 
@@ -45,6 +51,8 @@ def setup_data(self, data: pd.DataFrame) -> pd.DataFrame:
             else:
                 data["width"] = resolution(data["x"], False) * 0.9
 
+        just = self.params.get("just", 0.5)
+
         bool_idx = data["y"] < 0
 
         data["ymin"] = 0.0
@@ -53,7 +61,7 @@ def setup_data(self, data: pd.DataFrame) -> pd.DataFrame:
         data["ymax"] = data["y"]
         data.loc[bool_idx, "ymax"] = 0.0
 
-        data["xmin"] = data["x"] - data["width"] / 2
-        data["xmax"] = data["x"] + data["width"] / 2
+        data["xmin"] = data["x"] - data["width"] * just
+        data["xmax"] = data["x"] + data["width"] * (1 - just)
         del data["width"]
         return data

plotnine/geoms/geom_col.py

@@ -17,6 +17,11 @@ class geom_col(geom_bar):
     Parameters
     ----------
     {common_parameters}
+    just : float, default=0.5
+        How to align the column with respect to the axis breaks. The default
+        `0.5` aligns the center of the column with the break. `0` aligns the
+        left of the of the column with the break and `1` aligns the right of
+        the column with the break.
     width : float, default=None
         Bar width. If `None`{.py}, the width is set to
         `90%` of the resolution of the data.
@@ -32,5 +37,6 @@ class geom_col(geom_bar):
         "stat": "identity",
         "position": "stack",
         "na_rm": False,
+        "just": 0.5,
         "width": None,
     }

tests/baseline_images/test_geom_bar_col_histogram/col_just.png

@@ -40,6 +40,17 @@ def test_col():
     assert p == "col"
 
 
+def test_col_just():
+    data = pd.DataFrame({"x": range(1, 4), "y": range(1, 4)})
+    p = (
+        ggplot(data, aes("x", "y"))
+        + geom_col(just=0, fill="red", width=1 / 3)  # left
+        + geom_col(just=1, fill="blue", width=1 / 3)  # right
+        + geom_col(just=0.5, fill="green", width=1 / 3, alpha=0.7)  # center
+    )
+    assert p == "col_just"
+
+
 def test_histogram_count():
     p = ggplot(data, aes("x")) + geom_histogram(aes(fill="factor(z)"), bins=n)