Group by values and other groups

I need a help with the algorytm.

from the table

I would like to get the group names with its values, in case group contains another group values from this group

G1=V1,V2

G2=V1,V3

G3=V4

G4=V1,V3,V5

I need to write it in python but it can be any language

Here is an example program in python that looks to do what you need!
Edit: I see I've misinterpreted. Will edit again and add group.
program.py

file = open("file.csv", "r")
class link_arr():
    def __init__(self):
        self.linked_groups = []
        self.values = []
    def __str__(self):
        return str(self.values)
    def __repr__(self):
        return self.__str__()

output = {}
while True:
    line = file.readline()
    if line == '':
        break
    words = line.split(',')
    words = [w.strip() for w in words]
    if not words[0] in output:
        output[words[0]] = link_arr()
    if words[1] in output:
        output[words[1]].linked_groups.append(words[0])
        for val in output[words[1]].values:
            output[words[0]].values.append(val)
    else:
        output[words[0]].values.append(words[1])
    for group in output[words[0]].linked_groups:
        output[group].values.append(words[1])
print(output)

file.csv

G1,V1
G1,V2
G2,V1
G2,V3
G3,V4
G4,G2
G4,V5

output:

{'G1': ['V1', 'V2'], 'G2': ['V1', 'V3'], 'G3': ['V4'], 'G4': ['V1', 'V3', 'V5']}