From b3c7d687b7adbf9ae6fd1a2ac71a17405c3a52fd Mon Sep 17 00:00:00 2001
From: rstiskalek <richard.stiskalek@protonmail.com>
Date: Wed, 12 Oct 2022 11:47:11 +0100
Subject: [PATCH] add columns flip

---
 galomatch/io/__init__.py |  2 +-
 galomatch/io/readsim.py  | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/galomatch/io/__init__.py b/galomatch/io/__init__.py
index 3d34c77..26e9b4d 100644
--- a/galomatch/io/__init__.py
+++ b/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)
diff --git a/galomatch/io/readsim.py b/galomatch/io/readsim.py
index 4852218..2ef8f3f 100644
--- a/galomatch/io/readsim.py
+++ b/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