在group_by

Question

我有数据：

data = [["/","201408","41"],["/","201409","35"],["/","201410","59"],["/","201411","50"],["/","201412","79"],["/","201501","97"],["/","201502","85"],["/","201503","518"],["/","201504","251"],["/","201505","748"],["/","201506","916"],["/","201507","1008"],["/","201508","449"],["/","201509","235"],["/","201510","195"],["/","201511","229"],["/","201512","202"],["/","201601","142"],["/","201602","134"],["/","201603","17"]]

我想按年份对它们进行分组，但我不知道如何在group_by中使用正则表达式。我应该这样：

grouped = data.group_by { |row| row[1] }

但下一步是什么？ row [1]字符串是YYYYMM

Answer 1

为什么需要正则表达式？这不是你想要的吗？

data.group_by { |d| d[1][0..3] }

Answer 2

我更喜欢幻觉＆＃39;回答，但如果你还想使用正则表达式：
data.group_by { |row| row[1].match(/^(\d{4})/).captures[0] }

不是很干净，但是有效。