Matching/Sorting line terminations

Hi: The first difficulty with the problem I describe below is that I
don't know what the key terms would be to search Google accurately. I
have searched for a long time already. So if anyone could even tell me
what it is I am looking for I'd be very grateful.

The problem is this: I have a large file of poetry in alphabetical
order sorted on the last term in each line, I post an except in
sample1 below. I want to sort it so that lines that share, say, the
last two terms (on the right) with the last two terms of any other
line are in one group, those lines that share the last three terms in
another and so on up to seven places -- as in sample2 below.

The first difficulty I have is getting the search terms into an :ex
command -- I need to find for each line whether there are any others
that match it to seven terminal places, then to six and so on. I could
do the simple locating with something cumbersome like this:

map ö $BB2yW: p0ig/ A$/m0 map ä $ByW: p0ig/ A$/m0

and so on up to seven places. But it must be possible to generalize
that somehow. What would be the general form of an expression for
finding the last 'x' words of a line in the same position somewhere
else in the file?

Apart from the crudeness of the operation, the trouble would be
exporting (redirecting?) the results automatically and keeping the
exported results in order (as in sample2 below). And also how to
iterate it usefully through the whole file.

If I started at the top of the raw file, iterating something like
these commands, checking each line and exporting the results to a
single file, the resulting file would be identical to the original
file. I need, I think, to be able to eliminate those lines which do
not share any terminations with any other lines. I think starting
(somehow) with seven places then six and down to two, would leave me
the non-sharing lines by themselves in the original file(?).

But I'm not even sure what the strategic logic should be: exactly what
tasks should I be trying to get the program to perform? The process
needs to be automated because the file is 33,000 lines long. As I say,
if someone could tell me what key terms, what types of operations, I
should be looking for on Google, it would help a great deal.

Many thanks for any help, JBL
Vim 7.x Debian/Win7

Here are the samples, one before (from the raw file) and one after (as
I'd like the whole thing organized).

Raw Lines
6.4.30.7 All these our ioyes and all our blisse abate
2.12.15.9 And after them did driue with all her power and might
3.9.14.4 And both full liefe his boasting to abate
6.6.27.9 And layd at him amaine with all his will and might
6.1.38.2 At once did heaue with all their powre and might
6.1.12.7 But through misfortune which did me abase
5.11.57.9 Did set vpon those troupes with all his powre and might
6.2.26.5 For deare affection and vnfayned zeale
3.2.13.6 For hardy thing it is to weene by might
4.9.6.9 He her vnwares attacht and captiue held by might
6.1.32.9 He spide come pricking on with al his powre and might
6.6.31.9 He stayd his second strooke and did his hand abase
3.8.51.6 Mote not mislike you also to abate
3.8.28.7 Ne ought your burning fury mote abate
1.7.35.1 No magicke arts hereof had any might
5.8.46.8 She at her ran with all her force and might
1.10.2.8 She cast to bring him where he chearen might
3.7.35.3 That at the last his fiercenesse gan abate
4.8.17.8 That her inburning wrath she gan abate
1.10.47.7 That hill they scale with all their powre and might
4.6.3.4 The armes he bore his speare he gan abase
5.9.39.4 To all assayes; his name was called Zele
2.9.7.4 To serue that Queene with all my powre and might
2.1.26.7 When suddenly that warriour gan abace
6.12.23.9 Where he him found despoyling all with maine and might
1.5.1.8 With greatest honour he atchieuen might
4.8.1.7 With sufferaunce soft which rigour can abate
5.5.30.1 With that she turn'd her head as halfe abashed

Sorted lines
---Lines not repeating final term (=Unique lines):
FQ 2.1.26.7 When suddenly that warriour gan abace
FQ 5.5.30.1 With that she turn'd her head as halfe abashed
FQ 6.2.26.5 For deare affection and vnfayned zeale
FQ 5.9.39.4 To all assayes; his name was called Zele

---Lines repeating final term only:
FQ 6.1.12.7 But through misfortune which did me abase
FQ 6.6.31.9 He stayd his second strooke and did his hand abase
FQ 4.6.3.4 The armes he bore his speare he gan abase
FQ 3.8.28.7 Ne ought your burning fury mote abate
FQ 4.8.1.7 With sufferaunce soft which rigour can abate
FQ 6.4.30.7 All these our ioyes and all our blisse abate
FQ 1.7.35.1 No magicke arts hereof had any might
FQ 1.10.2.8 She cast to bring him where he chearen might
FQ 1.5.1.8 With greatest honour he atchieuen might
FQ 6.6.27.9 And layd at him amaine with all his will and might

---Lines repeating final two terms:
FQ 3.9.14.4 And both full liefe his boasting to abate
FQ 3.8.51.6 Mote not mislike you also to abate
FQ 4.8.17.8 That her inburning wrath she gan abate
FQ 3.7.35.3 That at the last his fiercenesse gan abate
FQ 3.2.13.6 For hardy thing it is to weene by might
FQ 4.9.6.9 He her vnwares attacht and captiue held by might

---Lines repeating final three terms:
FQ 5.8.46.8 She at her ran with all her force and might
FQ 6.12.23.9 Where he him found despoyling all with maine and might
FQ 2.9.7.4 To serue that Queene with all my powre and might
........

---Lines repeating final six terms:
FQ 2.12.15.9 And after them did driue with all her power and might
FQ 5.11.57.9 Did set vpon those troupes with all his powre and might
FQ 6.1.32.9 He spide come pricking on with all his powre and might
FQ 1.10.47.7 That hill they scale with all their powre and might
FQ 6.1.38.2 At once did heaue with all their powre and might

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