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我将两个时间变量“Interaction2”和“Start2”转换为周格式，以便我可以按周聚合我的数据集。我想创建第三个变量“Weeks”，它是“Interaction2”和“Start2”之间的区别。我使用以下命令将时间变量转换为标准日期格式的年、月、周（而不是年、月、日）：

d1$Interaction2<-format(d1$Interaction,'%Y-%m-%U')
d1$Start2<-format(d1$Start,'%Y-%m-%U')

“Interaction2”和“Start2”的结果似乎格式正确，但它们是字符变量。我使用 difftime 函数来获得差异，但结果是小数：

d1$Weeks<-difftime(d1$Interaction2,d1$Start2,units='weeks')

结果不应该是整数吗？difftime 命令是否将最后两位数字解释为一天而不是一周？如何获得“Interaction2”周和“Start2”周之间的周数差异？

structure(list(Interaction2 = c("2015-02-06", "2015-02-08", "2015-03-09", 
"2015-03-11", "2015-03-12"), Start2 = c("1995-04-16", "1995-04-16", 
"1995-04-16", "1995-04-16", "1995-04-16"), Weeks = structure(c(1033.72023809524, 
1034.00595238095, 1038.14285714286, 1038.42857142857, 1038.57142857143
), units = "weeks", class = "difftime")), .Names = c("Interaction2", 
"Start2", "Weeks"), row.names = c(NA, 5L), class = "data.frame")

在运行差异命令之前，我还尝试使用 strptime 转换字符变量：

d1$Interaction3<-strptime(as.character(d1$Interaction2),"%Y%m%U")
d1$Start3<-strptime(as.character(d1$Start2),"%Y%m%U")
d1$Weeks<-difftime(d1$Interaction3,d1$Start3,units='weeks')

但这导致了“Interaction3”、“Start3”和“Weeks”变量的 NA：

structure(list(Interaction2 = c("2015-02-06", "2015-02-08", "2015-03-09", 
"2015-03-11", "2015-03-12"), Start2 = c("1995-04-16", "1995-04-16", 
"1995-04-16", "1995-04-16", "1995-04-16"), Weeks = structure(c(NA_real_, 
NA_real_, NA_real_, NA_real_, NA_real_), units = "weeks", class = "difftime"), 
Start3 = structure(list(sec = c(NA_real_, NA_real_, NA_real_, 
NA_real_, NA_real_), min = c(NA_integer_, NA_integer_, NA_integer_, 
NA_integer_, NA_integer_), hour = c(NA_integer_, NA_integer_, 
NA_integer_, NA_integer_, NA_integer_), mday = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_), mon = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_), year = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_), wday = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_), yday = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_), isdst = c(-1L, 
-1L, -1L, -1L, -1L), zone = c("", "", "", "", ""), gmtoff = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_)), .Names = c("sec", 
"min", "hour", "mday", "mon", "year", "wday", "yday", "isdst", 
"zone", "gmtoff"), class = c("POSIXlt", "POSIXt")), Interaction3 = structure(list(
sec = c(NA_real_, NA_real_, NA_real_, NA_real_, NA_real_
), min = c(NA_integer_, NA_integer_, NA_integer_, NA_integer_, 
NA_integer_), hour = c(NA_integer_, NA_integer_, NA_integer_, 
NA_integer_, NA_integer_), mday = c(NA_integer_, NA_integer_, 
NA_integer_, NA_integer_, NA_integer_), mon = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_), 
year = c(NA_integer_, NA_integer_, NA_integer_, NA_integer_, 
NA_integer_), wday = c(NA_integer_, NA_integer_, NA_integer_, 
NA_integer_, NA_integer_), yday = c(NA_integer_, NA_integer_, 
NA_integer_, NA_integer_, NA_integer_), isdst = c(-1L, 
-1L, -1L, -1L, -1L), zone = c("", "", "", "", ""), gmtoff = c(NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_)), .Names = c("sec", 
"min", "hour", "mday", "mon", "year", "wday", "yday", "isdst", 
"zone", "gmtoff"), class = c("POSIXlt", "POSIXt"))), .Names = c("Interaction2", 
"Start2", "Weeks", "Start3", "Interaction3"), row.names = c(NA, 
5L), class = "data.frame")
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1 回答 1

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试试这个（添加单位参数），它依赖于 difftime 隐式地将字符变量强制转换为数字变量（POSIXct）并取数值差异：

> difftime( mydf$Interaction2,mydf$Start2, units="weeks")
Time differences in weeks
[1] 1033.720 1034.006 1038.143 1038.429 1038.571
于 2015-06-07T22:32:23.073 回答