For example this list:
[['software', 'foundation'], ['of', 'the'], ['the', 'python'], ['software', 'foundation'],['of', 'the'], ['software', 'foundation']]
# 进行频率统计,例如输出结果为:
("['software','foundation']", 3), ("['of', 'the']", 2), ("['the', 'python']", 1)