Use pandas DF to hold data in Bunch class

Use pandas DF to hold data in Bunch class instead of numpy masked array -> better behaviour and allows to set to alive particles only

Tracking/beam.py

@@ -7,7 +7,7 @@ Beam and bunch elements
 """
 
 import numpy as np
-import numpy.ma as ma
+import pandas as pd
 import warnings
 
 class Bunch:
@@ -45,33 +45,38 @@ class Bunch:
     """
     
     def __init__(self, ring, mp_number=1e3, current=1e-3):
-        dpart = np.dtype([("x",np.float64),("xp",np.float64),
-                          ("y",np.float64),("yp",np.float64),
-                          ("tau",np.float64),("delta",np.float64)])
-        self.dtype = dpart
-        particles = np.zeros((int(mp_number),6), dtype=np.float64)
-        self.particles = ma.masked_array(particles)
-        
+        particles = {"x":np.zeros((int(mp_number),)),
+                     "xp":np.zeros((int(mp_number),)),
+                     "y":np.zeros((int(mp_number),)),
+                     "yp":np.zeros((int(mp_number),)),
+                     "tau":np.zeros((int(mp_number),)),
+                     "delta":np.zeros((int(mp_number),)),
+                     }
+        self.particles = pd.DataFrame(particles)
+        self.alive = pd.Series(np.ones((int(mp_number),),dtype=bool))
         self.ring = ring
         self._mp_number = int(mp_number)
         self.current = current
         
     def __len__(self):
         """Return the number of alive particles"""
-        #mask = self.particles["alive"] == True
-        return len(self.particles)
+        return len(self[:])
         
-    def __getitem__(self, i):
-        """Return the alive particle number i"""
-        return self.particles[i]
+    def __getitem__(self, label):
+        """Return the columns label for alive particles"""
+        return self.particles.loc[self.alive, label]
     
-    def __setitem__(self, i, value):
-        """Set value to the alive particle number i"""
-        self.particles[i] = value
+    def __setitem__(self, label, value):
+        """Set value to the columns label for alive particles"""
+        self.particles.loc[self.alive, label] = value
     
     def __iter__(self):
-        """Iterate over alive particles"""
-        return self.particles.__iter__()
+        """Iterate over labels"""
+        return self[:].__iter__()
+    
+    def __repr__(self):
+        """Return representation of alive particles"""
+        return f'{self[:]!r}'
         
     @property
     def mp_number(self):
@@ -129,7 +134,7 @@ class Bunch:
         mean : numpy array
             mean position of alive particles
         """
-        mean = [[self[name].mean()] for name in self.dtype.names]
+        mean = [[self[name].mean()] for name in self]
         return np.array(mean)
     
     def std(self):
@@ -142,7 +147,7 @@ class Bunch:
         std : numpy array
             standard deviation of the position of alive particles
         """
-        std = [[self[name].std()] for name in self.dtype.names]
+        std = [[self[name].std()] for name in self]
         return np.array(std)
         
     def emit(self):