Add preliminary example

Author: franzpoeschel

examples/15_scipp_loader.py

@@ -1,9 +1,48 @@
 import openpmd_api as pmd
+import openpmd_api.scipp as pmdsc
+import scipp as sc
 
 
 def main():
-    series = pmd.Series("./out.bp5", pmd.Access.read_only)
+    series = pmd.Series("../samples/git-sample/data%T.h5", pmd.Access.read_only)
+
+    time = 65 * sc.Unit("fs")
     scipp_loader = series.to_scipp()
+    print(scipp_loader.iterations)
+    Ex = scipp_loader.get_field("E", "x", time=time)
+    print(Ex)
+    slicing_idx = pmdsc.closest(Ex, "x", 2 * sc.Unit("um"))
+    Ex_slice = Ex["x", slicing_idx]
+    print(Ex_slice)
+    Ex_slice.plot().save("slice.png")
+    Ex_line = Ex_slice["z", pmdsc.closest(Ex_slice, "z", 1.4e-5 * sc.Unit("m"))]
+    print(Ex_line)
+    Ex_line.plot().save("line.png")
+    (Ex_line * Ex_line).plot().save("line_squared.png")
+
+    # The full 3D array is not loaded into memory at this point.
+    Ex = scipp_loader.get_field("E", "x", time=time, relay=True)
+    # This time we will select a range rather than a slice.
+    # For a range there is no need for an exact match.
+    # But, we could also select a slice just like in the previous example.
+    Ex = Ex["x", -2e-6 * sc.Unit("m") : 2e-6 * sc.Unit("m")]
+    # Only now the smaller subset wil be loaded into memory
+    Ex = Ex.load_data()
+    print(Ex)
+
+    Ex = sc.concat(
+        [
+            scipp_loader.get_field("E", "x", iteration=iteration.value, time_tolerance=None)
+            for iteration in scipp_loader.iterations["iteration_id"]
+        ],
+        dim="t",
+    )
+    print(Ex)
+
+    # Let us just slice at some points to get a 2D dataset
+    Ex = Ex["x", 10]["y", 10]
+    print(Ex)
+    Ex.plot().save("moving_window.png")
 
 if __name__ == "__main__":
     main()