// k2 vector

t:0 0 0 2 2 2 4 4 7 7           / tree
c:#t                            / count of tree
n:!c                            / nodes (labels)
f:50<                           / predicate
l:~n _lin t                     / leaves
d:l*(c _draw 100)%l             / data (NaN at non-leaves)
b:&l&f d                        / leaves where f
p:t\'b                          / paths to leaves where f
N:{x@<x}@?,//p                  / subtree labels
z:&#N                           / zeros
i:N?/:/:p                       / path indices (renumbering)
k:,'/(-1 1_'2#,:)'i             / path indices -> pairwise links
T:@[z;*k;:;k 1]                 / subtree = renumbered tree
D:@[z%z;i[;0];:;d b]            / subtree data

/ pretty print
pp:{`0:{(x$z)," ",$y}'[#:'x\'!#x;y;z]}

\

pp[t;d;n]
  
0
 1 51
 2
  3 34
  4
  5 51
   6 29
   7
    8 17
    9 89

pp[T;D;N] 

0
 1 51
 2
  4
  5 51
   7
    9 89

/ big tree (~500000 nodes, 10000 leaves)
t:0,&10000_draw 100