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I currently use TNF100-1 simulation data, and want to sort a dataset from all subhaloes with all keys in z=0.

And I am not sure how to access primary halo mass of subhalo

Here is my code

import pandas as pd
import numpy as np
import illustris_python as il
basePath = '/Users/glin/TNG100-1/output/'
header = il.groupcat.loadHeader(basePath, 99)
print('Available fields:', list(header.keys()))

subhalos = il.groupcat.loadSubhalos(basePath, 99)
halos = il.groupcat.loadHalos(basePath, 99, fields=['GroupFirstSub', 'Group_M_Crit200'])
primary_halo_mass = np.zeros(subhalos['count'])

for i in range(subhalos['count']):
    # Find Subhalo's group
    group_id = subhalos['SubhaloGrNr'][i]
    # find the group's primary subhalo
    primary_subhalo_id = halos['GroupFirstSub'][group_id]    
    # primary halo mass
    if primary_subhalo_id >= 0:
        primary_halo_mass[i] = halos['Group_M_Crit200'][group_id] * 1e10 / 0.704
    else
        primary_halo_mass[i] = 0

subhalo_data['PrimaryHaloMass'] = primary_halo_mass

Did I sort the right primary_halo_mass to subhalos?
Thanks

You want to calculate: for each subhalo (including satellites), the M200c mass of its parent halo?

Then this should just be:

primary_halo_mass = np.zeros(subhalos['count'], dtype='float32')

for i in range(subhalos['count']):
    # Find Subhalo's group
    group_id = subhalos['SubhaloGrNr'][i]
    # primary halo mass
    primary_halo_mass[i] = halos['Group_M_Crit200'][group_id] * 1e10 / 0.704

but it can also be done simply without loops:

primary_halo_mass = halos['Group_M_Crit200'][subhalos['SubhaloGrNr']]