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I get the read the subfindID. But when I want to read the detailed information about it through its subfindID.
I get the subfindID from the code:

def trans(basePath,subhaloID,SnapNum,id):
    '''try to get the subfindID from its subhaloID'''
    RowNum, LastProgID, SubhaloID = il.sublink.treeOffsets(basePath, SnapNum, id, "SubLink")
    rowStart = RowNum
    rowEnd   = RowNum + (LastProgID - SubhaloID)
    nRows    = rowEnd - rowStart + 1
    offsets = il.sublink.subLinkOffsets(basePath, "SubLink", True)
    rowOffsets = rowStart - offsets
    fileNum = np.max(np.where(rowOffsets >= 0))
    subhaloID=subhaloID%1000000
    with h5py.File(il.sublink.treePath(basePath, "SubLink", fileNum), 'r') as f:
        SubfindID=f['SubfindID'][subhaloID]
    return SubfindID

and I want to use it in loadSingle, but it has the error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-8-9083be1f37e1> in <module>
      4     if i in cut:
      5         continue
----> 6     cosI=angular(basePath,mergerlist[2*i],mergerlist[2*i+1],snap)
      7     total.append(cosI)

<ipython-input-3-3e61878b4f88> in angular(basePath, SubfindID1, SubfindID2, SnapNum)
      2     '''know the cos of the two galaxies' angular monmentous '''
      3     sub1=il.groupcat.loadSingle(basePath, SnapNum, haloID=-1,subhaloID=SubfindID1)
----> 4     sub2=il.groupcat.loadSingle(basePath, SnapNum, haloID=-1,subhaloID=SubfindID2)
      5     L1=sub1['SubhaloMass']*sub1['SubhaloSpin']
      6     L2=sub2['SubhaloMass']*sub2['SubhaloSpin']

~/illustris_python/groupcat.py in loadSingle(basePath, snapNum, haloID, subhaloID)
    152     with h5py.File(gcPath(basePath, snapNum, fileNum), 'r') as f:
    153         for haloProp in f[gName].keys():
--> 154             result[haloProp] = f[gName][haloProp][groupOffset]
    155 
    156     return result

h5py/_objects.pyx in h5py._objects.with_phil.wrapper()

h5py/_objects.pyx in h5py._objects.with_phil.wrapper()

/opt/conda/lib/python3.6/site-packages/h5py/_hl/dataset.py in __getitem__(self, args)
    474 
    475         # Perform the dataspace selection.
--> 476         selection = sel.select(self.shape, args, dsid=self.id)
    477 
    478         if selection.nselect == 0:

/opt/conda/lib/python3.6/site-packages/h5py/_hl/selections.py in select(shape, args, dsid)
     92 
     93     sel = SimpleSelection(shape)
---> 94     sel[args]
     95     return sel
     96 

/opt/conda/lib/python3.6/site-packages/h5py/_hl/selections.py in __getitem__(self, args)
    259             return self
    260 
--> 261         start, count, step, scalar = _handle_simple(self.shape,args)
    262 
    263         self._id.select_hyperslab(start, count, step)

/opt/conda/lib/python3.6/site-packages/h5py/_hl/selections.py in _handle_simple(shape, args)
    449         else:
    450             try:
--> 451                 x,y,z = _translate_int(int(arg), length)
    452                 s = True
    453             except TypeError:

/opt/conda/lib/python3.6/site-packages/h5py/_hl/selections.py in _translate_int(exp, length)
    469 
    470     if not 0<=exp<length:
--> 471         raise ValueError("Index (%s) out of range (0-%s)" % (exp, length-1))
    472 
    473     return exp, 1, 1

ValueError: Index (62467) out of range (0-14077)

so what's wrong, please help me

I am not sure what the trans() function is trying to do?

And what does subhaloID=subhaloID%1000000 mean?

Dear sir,
the trans() function trys get the subfindID of the NextProgenitor which comes from tree. And for subhaloID=subhaloID%1000000 , it's used to read the index of the Nextprogenitor.

For example

In [3]: tree = il.sublink.loadTree(basePath, snap_num, subhalo_id)

In [8]: tree['FirstProgenitorID'][0]
Out[8]: 257735

In [9]: ww = np.where(tree['SubhaloID'] == 257735)

In [10]: ww
Out[10]: (array([1]),)

In [13]: tree['NextProgenitorID'][1]
Out[13]: 258657

In [14]: ww = np.where(tree['SubhaloID'] == 258657)

In [15]: ww
Out[15]: (array([923]),)

In [16]: tree['SubfindID'][923]
Out[16]: ANSWER

but it maybe unread because the ww of np.where(tree['SubhaloID'] == 258657) equals array[].

By definition, if you specify onlyMPB=True when loading the tree, then the result does not contain any Next Progenitors.

If you want to explore the full tree, and not just the Main Progenitor Branch, you should delete onlyMPB=True.

Dear Sir,
I have a try in my code. But in 33snapshot,the array is empty.
why is the shape of the subhalo smaller than the NextProgenitorID?

You cannot access tree['NextProgenitorID'][0], this is undefined (for the root node).

You should first access tree['FirstProgenitorID'][0], which is 1, then tree['NextProgenitorID'][1], which is 52265.