1) Under which condition should the algorithm switch to build another group ? (as soon as we meet a X-Y link that is below the threshold ? other ?)

2) Do the order matter inside a line ?
(In other words : is it correct to assume that X-Y can be considered the same way as Y-X) ?

3) Do the order matter between lines ? (in think it does in order to preserve the chaining of pairs... is that correct ?)

---------- Post updated at 10:09 AM ---------- Previous update was at 09:54 AM ----------

Let's start a "kind of" pseudo-code:

Let's say we are going to build some Groups :
G[1]
G[2]
...

Let's start with G[1]
while scanning your input file line by line :
if G[1] is empty, then put G[1]=$1" "$2
if G[1] is not empty, let's check the scanned line :
if $1 is in G[1] and $2 is not : then add $2 into that group
if $2 is in G[1] and $1 is not : then add $1 into that group
if both are in it : ignore it an process next line (should we consider it as a breaking sequence so that we start a new group ?)
if none are in it : build next group : G[++c]=$1 FS $2

Is that algo correct ?

if so, the following :

A D 90
E D 90
C F 90
D C 90

would generate 2 Groups sequence :

A D E
C F D

And not

A D E C F

So before coding, you must think of what logic and what condition should apply for breaking the sequence and/or switch to a new group.

Thanks in advance for clarifing your requirements at first.