add columns flip

galomatch/io/__init__.py

@@ -15,4 +15,4 @@
 
 from .readsim import (get_sim_path, open_particle, open_unbinding,
                       read_particle, read_clumpid, read_clumps,
-                      convert_mass_cols, convert_position_cols)
+                      convert_mass_cols, convert_position_cols, flip_cols)

galomatch/io/readsim.py

@@ -363,3 +363,27 @@ def convert_position_cols(arr, cols, zero_centered=False):
         arr[col] *= BOXSIZE
         if zero_centered:
             arr[col] -= BOXSIZE / 2
+
+
+def flip_cols(arr, col1, col2):
+    """
+    Flip values in columns `col1` and `col2`. `arr` is passed by reference and
+    is not explicitly returned back.
+
+
+    Parameters
+    ----------
+    arr : structured array
+        The array whose columns are to be converted.
+    col1 : str
+        The first column name.
+    col2 : str
+        The second column name.
+
+    Returns
+    -------
+    nothing
+    """
+    dum = numpy.copy(arr[col1])
+    arr[col1] = arr[col2]
+    arr[col2] = dum