请问在正则表达式中，提取多个数值中的某一个怎么写？

Question

比如

内容1：[8175.6,0.0085],[8175.1,0.55],[8175,2.5],[8174.9,1.5],[8174.8,0.814],[8172.1,0.2],[8171.8,0.356],[8171.6,1.32],[8171.5,0.8],[8171.2,0.0615],[8171.1,0.0025],[8170.9,0.2],[8170.2,0.5],[8169.7,0.3843],[8169.6,0.6858],[8169.4,1.836],[8169.2,0.4],[8168.9,0.5152],[8168.8,0.2],[8167.9,0.4],[8167.8,0.4],[8167.5,0.3396],[8165.3,0.2423],[8165.2,0.2],[8165.1,11.1044]

内容2：[8165,8.8056], [8164.9,0.0864], [8164.7,0.48], [8164,0.48], [8163.3,0.0911], [8162,0.009], [8161.7,0.003], [8161.4,4.3], [8161.3,3], [8161,0.55], [8160.8,0.4], [8160.7,0.4], [8160,5.8816], [8159.8,13.0436], [8159.3,0.02], [8159.1,0.0433], [8159,0.4], [8158.8,0.0705], [8158.7,0.4], [8158.5,2.5013], [8156.2,12.5], [8155.3,0.02], [8155.1,0.9989], [8155,11.102], [8153.4,1]

取内容1中第一个数值：8175.6,0.0085 或[8175.6,0.0085]
取内容2中第一个数值：8165,8.8056 或[8165,8.8056]

表达式该怎么写？如果是取最后一个数值，或者其中某个数值呢？
谢谢各位帮忙，十分感激