Add method to write new snapshot that contains a subset of another snapshot's molecules.

cmeutils/gsd_utils.py

@@ -380,6 +380,131 @@
     print(f"XML data written to {gsdfile}")
 
 
+def trim_snapshot_molecules(parent_snapshot, mol_indices):
+    """Given a snapshot of a system, trim the snapshot to only include
+    a subset of the molecules.
+
+    Parameters
+    ----------
+    parent_snapshot : gsd.hoomd.Frame
+        The snapshot to read in.
+    mol_indices : list of np.ndarray
+        List of arrays where each array contains the indices
+        of the particles in a molecule to include.
+
+    Returns
+    -------
+    gsd.hoomd.Frame
+        The new snapshot with only the specified molecules.
+
+    Notes
+    -----
+    See cmetuils.gsd_utils.get_molecule_cluster for a method to obtain
+    mol_indices.
+
+    """
+    new_snap = gsd.hoomd.Frame()
+    new_snap.configuration.box = parent_snapshot.configuration.box
+    new_snap.particles.N = sum(len(i) for i in mol_indices)
+
+    # Write out particle info
+    for attr in [
+        "position",
+        "mass",
+        "velocity",
+        "orientation",
+        "image",
+        "diameter",
+        "angmom",
+        "typeid",
+    ]:
+        setattr(
+            new_snap.particles,
+            attr,
+            np.concatenate(
+                list(
+                    getattr(parent_snapshot.particles, attr)[i]
+                    for i in mol_indices
+                )
+            ),
+        )
+    new_snap.particles.types = parent_snapshot.particles.types
+
+    particle_index_map = dict()
+    count = 0
+    for indices in mol_indices:
+        for i in indices:
+            particle_index_map[i] = count
+            count += 1
+
+    # Write out bond info
+    mol_bond_groups = []
+    mol_bond_ids = []
+    for indices in mol_indices:
+        mask = np.any(
+            np.isin(parent_snapshot.bonds.group, indices.flatten()), axis=1
+        )
+        parent_mol_bonds = parent_snapshot.bonds.group[np.where(mask)[0]]
+        parent_mol_bond_typeids = parent_snapshot.bonds.typeid[
+            np.where(mask)[0]
+        ]
+        new_mol_bonds = np.vectorize(particle_index_map.get)(parent_mol_bonds)
+        mol_bond_groups.append(new_mol_bonds)
+        mol_bond_ids.append(parent_mol_bond_typeids)
+
+    new_snap.bonds.types = parent_snapshot.bonds.types
+    new_snap.bonds.group = np.concatenate(mol_bond_groups)
+    new_snap.bonds.typeid = np.concatenate(mol_bond_ids)
+    new_snap.bonds.N = sum(len(i) for i in mol_bond_ids)
+
+    # Write out angle info
+    mol_angle_groups = []
+    mol_angle_ids = []
+    for indices in mol_indices:
+        mask = np.any(
+            np.isin(parent_snapshot.angles.group, indices.flatten()), axis=1
+        )
+        parent_mol_angles = parent_snapshot.angles.group[np.where(mask)[0]]
+        parent_mol_angle_typeids = parent_snapshot.angles.typeid[
+            np.where(mask)[0]
+        ]
+        new_mol_angles = np.vectorize(particle_index_map.get)(parent_mol_angles)
+        mol_angle_groups.append(new_mol_angles)
+        mol_angle_ids.append(parent_mol_angle_typeids)
+
+    new_snap.angles.types = parent_snapshot.angles.types
+    new_snap.angles.group = np.concatenate(mol_angle_groups)
+    new_snap.angles.typeid = np.concatenate(mol_angle_ids)
+    new_snap.angles.N = sum(len(i) for i in mol_angle_ids)
+
+    # Write out dihedral info
+    mol_dihedral_groups = []
+    mol_dihedral_ids = []
+    for indices in mol_indices:
+        mask = np.any(
+            np.isin(parent_snapshot.dihedrals.group, indices.flatten()), axis=1
+        )
+        parent_mol_dihedrals = parent_snapshot.dihedrals.group[
+            np.where(mask)[0]
+        ]
+        parent_mol_dihedral_typeids = parent_snapshot.dihedrals.typeid[
+            np.where(mask)[0]
+        ]
+        new_mol_dihedrals = np.vectorize(particle_index_map.get)(
+            parent_mol_dihedrals
+        )
+        mol_dihedral_groups.append(new_mol_dihedrals)
+        mol_dihedral_ids.append(parent_mol_dihedral_typeids)
+
+    new_snap.dihedrals.types = parent_snapshot.dihedrals.types
+    new_snap.dihedrals.group = np.concatenate(mol_dihedral_groups)
+    new_snap.dihedrals.typeid = np.concatenate(mol_dihedral_ids)
+    new_snap.dihedrals.N = sum(len(i) for i in mol_dihedral_ids)
+
+    new_snap.validate()
+    return new_snap
+
+
 def identify_snapshot_connections(snapshot):
     """Identify angle and dihedral connections in a snapshot from bonds.