http://cos.name/cn/topic/108836

108836.R

x = read.csv('http://www.dataanalysis.cn/doc/a/1/qq.csv')[, -1]
x$time = as.POSIXct(x$time, format = '%Y/%m/%d %H:%M:%S', tz = 'GMT+8')
summary(x$id)[1:10]
#        7cha18        6cha4376        4cha3875         8cha083         4cha698 
#          1511            1238            1100             695             533 
#     1cha65314 acha@vip.qq.com           2cha1          5cha80        3cha4233 
#           440             380             354             304             300 
x$time = as.factor(as.Date(x$time, tz = 'GMT+8'))
summary(unique(x)$id)[1:10]
#      6cha4376        4cha3875          7cha18 acha@vip.qq.com         4cha698 
#           165             152             112              92              89 
#         2cha1         8cha083         1cha457       1cha59002          8cha08 
#            79              75              58              53              50