source	target	value	group_color2
A	a	12	grey
A	b	12	grey
B	c	32	grey
B	d	16	grey
B	a	32	grey
C	b	26	grey
C	c	41	grey
C	d	3	grey
C	a	12	grey
D	b	23	grey
a	1	41	grey
a	2	53	grey
a	3	25	grey
b	4	65	grey
c	5	23	grey
d	1	31	grey