Clarity individual table sorting requirements before subset

[hyanwong]

This confused me, and was the reason that I couldn't canonicalise node 0 such that it pointed to individual 0 (see below and message on slack):

import tskit
print("Tskit version:", tskit.__version__)
ts = tskit.load("canonicalize_issue.trees")
print("Node in orig ts:", ts.node(0))
tables = ts.dump_tables()
tables.canonicalise()
print("Node in canonicalised ts (which I am trying to force with individual id=0):", tables.nodes[0])
ts = tables.tree_sequence()
print("Actual individual 0 in canonicalised has the following nodes:", ts.individual(0).nodes)

Tskit version: 1.0.0
Node in orig ts: Node(id=0, flags=1, time=0.0, population=0, individual=7, metadata=b'')
Node in canonicalised ts (which I am trying to force with individual id=0): NodeTableRow(flags=1, time=0.0, population=0, individual=7, metadata=b'')
Actual individual 0 in canonicalised has the following nodes: [46 47]

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.76%. Comparing base (25a26a7) to head (d37fe17).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3355   +/-   ##
=======================================
  Coverage   89.76%   89.76%           
=======================================
  Files          29       29           
  Lines       31292    31292           
  Branches     5738     5738           
=======================================
  Hits        28089    28089           
  Misses       1794     1794           
  Partials     1409     1409           

Flag	Coverage Δ
c-tests	86.77% <ø> (ø)
lwt-tests	80.38% <ø> (ø)
python-c-tests	87.12% <ø> (ø)
python-tests	98.85% <ø> (ø)
python-tests-no-jit	33.51% <ø> (ø)
python-tests-numpy1	50.28% <ø> (ø)

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Files with missing lines	Coverage Δ
python/tskit/tables.py	99.77% <ø> (ø)
python/tskit/trees.py	98.89% <ø> (ø)

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[petrelharp]

Mind pointing to the part(s) of the code from which we know this is accurate?