Add a gallery example showing the usage of vertical and horizontal ba…

…rs (GenericMappingTools#1521)

Co-authored-by: Dongdong Tian <[email protected]>
Co-authored-by: Yvonne Fröhlich <[email protected]>

examples/gallery/symbols/bars.py

@@ -0,0 +1,71 @@
+r"""
+Vertical or horizontal bars
+---------------------------
+The :meth:`pygmt.Figure.plot` method can plot vertical (**b**) or
+horizontal (**B**) bars by passing the corresponding shortcut to
+the ``style`` parameter. By default, *base* = 0 meaning that the
+bar is starting from 0. Append **+b**\[*base*] to change this
+value. To plot multi-band bars, please append
+**+v**\|\ **i**\ *ny* (for verticals bars) or **+v**\|\ **i**\ *nx*
+(for horizontal ones), where *ny* or *nx* indicate the total
+number of bands in the bar (and hence the number of values required
+to follow the *x,y* coordinate pair in the input). Here, **+i**
+means we must accumulate the bar values from the increments
+*dy* or *dx*, while **+v** means we get the complete values relative
+to base. Normally, the bands are plotted as sections of a final
+single bar. Use **+s** to instead split the bar into *ny* or *nx*
+side-by-side, individual and thinner bars. Multi-band bars require
+``cmap=True`` with one color per band.
+"""
+
+import pygmt
+
+fig = pygmt.Figure()
+
+pygmt.makecpt(cmap="roma", series=[0, 4, 1])
+
+with fig.subplot(
+    nrows=2,
+    ncols=2,
+    subsize=("8c", "4c"),
+    frame="ag",
+    sharey=True,
+    sharex=True,
+    margins=["0.5c", "0.75c"],
+):
+
+    pen = "1.5p"
+    with fig.set_panel(panel=0):
+        color = "skyblue"
+        fig.basemap(region=[0, 4, 0, 3], frame="+tvertical bars")
+        fig.plot(x=1, y=2, style="b0.5c", color=color, pen=pen)
+        fig.plot(x=2, y=2.5, style="b1c", color=color, pen=pen)
+        # +b1 means that the bar is starting from y=1 here
+        fig.plot(x=3, y=2.5, style="b0.75c+b1", color=color, pen=pen)
+
+    with fig.set_panel(panel=1):
+        color = "tomato"
+        fig.basemap(region=[0, 4, 0, 3], frame="+thorizontal bars")
+        fig.plot(x=1.5, y=0.5, style="B0.75c", color=color, pen=pen)
+        fig.plot(x=3, y=1.5, style="B1c", color=color, pen=pen)
+        # +b2 means that the bar is starting from x=2 here
+        fig.plot(x=3.5, y=2.5, style="B0.5c+b2", color=color, pen=pen)
+
+    # generate dictionary for plotting multi-band bars
+    data = {
+        "x1": [0.25, 1.25],
+        "y": [1, 2],
+        "x2": [0.65, 0.5],
+        "x3": [0.4, 1.25],
+        "x4": [2.25, 0.75],
+    }
+
+    with fig.set_panel(panel=2):
+        fig.basemap(region=[0, 4, 0, 3], frame="+tstacked bars")
+        fig.plot(data=data, style="B0.75c+i4", cmap=True, pen=pen)
+
+    with fig.set_panel(panel=3):
+        fig.basemap(region=[0, 4, 0, 3], frame="+tsplit bars")
+        fig.plot(data=data, style="B1c+v4+s", cmap=True, pen=pen)
+
+fig.show()