这就是我的数据帧的样子。最右边的列(" TimeForLevelChange")是我想要的列。当给定名称的级别发生变化时,我想从先前级别获取最小日期,并从发生级别变化的行中取出日期并计算差异。所以在第三排,约翰的等级从1变为2,他在等级1中花了16天(2016-01-17 - 2016-01-01),然后再改为等级2.
library(data.table)
dt <- fread('
Name Level Date RecentLevelChange TimeForLevelChange
John 1 2016-01-01 NA NA
John 1 2016-01-10 NA NA
John 2 2016-01-17 1->2 16
John 2 2016-01-18 NA NA
John 3 2016-01-22 2->3 5
John 4 2016-01-26 3->4 4
John 4 2016-01-27 NA NA
John 7 2016-01-29 4->7 3
Tom 1 2016-01-10 NA NA
Tom 2 2016-01-17 1->2 7
Tom 2 2016-01-18 NA NA
Tom 3 2016-01-22 2->3 5
Tom 4 2016-01-26 3->4 4
Tom 4 2016-01-27 NA NA
Tom 7 2016-01-29 4->7 3
')
dt[, Date := as.IDate(Date)]
我可以在data.table中使用shift函数但我不知道如何为给定名称定义先前级别的最小日期。
答案 0 :(得分:7)
我可能会这样做
spell = dt[,{.(
w = .I[1L],
Date = Date[1L]
)}, by=.(Name, rleid(Level))][, .(
w = tail(w,-1),
d = diff(Date)
), by=Name]
dt[spell$w, dur_lastspell := spell$d]
给出了
Name Level Date RecentLevelChange TimeForLevelChange dur_lastspell
1: John 1 2016-01-01 NA NA NA days
2: John 1 2016-01-10 NA NA NA days
3: John 2 2016-01-17 1->2 16 16 days
4: John 2 2016-01-18 NA NA NA days
5: John 3 2016-01-22 2->3 5 5 days
6: John 4 2016-01-26 3->4 4 4 days
7: John 4 2016-01-27 NA NA NA days
8: John 7 2016-01-29 4->7 3 3 days
9: Tom 1 2016-01-10 NA NA NA days
10: Tom 2 2016-01-17 1->2 7 7 days
11: Tom 2 2016-01-18 NA NA NA days
12: Tom 3 2016-01-22 2->3 5 5 days
13: Tom 4 2016-01-26 3->4 4 4 days
14: Tom 4 2016-01-27 NA NA NA days
15: Tom 7 2016-01-29 4->7 3 3 days
我使用{.()}
代替.()
,因为后者会出错。我会将其报告为错误。