我正在尝试对数据表进行子集化。下面的代码工作正常，没有打嗝（我已经简化了它，试图找出它不会编织的原因）。我有一个包含2列的数据表，
Classes ‘data.table’ and 'data.frame': 7388 obs. of 2 variables:
$ Time : POSIXct, format: "2016-07-05 16:10:18" "2016-07-05 16:12:15" "2016-07-05 16:16:27" ...
$ Viewers: int 5923 6006 6109 5925 5708 5829 5989 6007 5963 5980 ...
- attr(*, ".internal.selfref")=<externalptr>
然后我得到一年中的某一天并将其转换为一个因子，并将时间列转换为包含星期几的因子：
weekly_cut$day_of_year<-factor(format(weekly_cut$Time,"%j"))
weekly_cut$Time<-factor(format(weekly_cut$Time,"%A"))
weekly_cut此时如下：
Classes ‘data.table’ and 'data.frame': 7388 obs. of 3 variables:
$ Time : Factor w/ 7 levels "Friday","Monday",..: 6 6 6 6 6 6 6 6 6 6 ...
$ Viewers : int 5923 6006 6109 5925 5708 5829 5989 6007 5963 5980 ...
$ day_of_year: Factor w/ 27 levels "187","188","189",..: 1 1 1 1 1 1 1 1 1 1 ...
- attr(*, ".internal.selfref")=<externalptr>
然后我生成一个新的数据表，其中包含按年份平均的观看者：
daily_averages<-weekly_cut[,.(average_viewers=mean(Viewers)),by=day_of_year]
一切正常，RStudio没有错误，但是当我编织时：
Quitting from lines 330-346 (index.Rmd)
Error in `[.xts`(weekly_cut, , .(average_viewers = mean(Viewers)), by = day_of_year) :
could not find function "."
Calls: <Anonymous> ... withCallingHandlers -> withVisible -> eval -> eval -> [ -> [.xts
Execution halted
请指教，谢谢！
EDIT1和2：
以下是dput(weekly_cut_small)的输出：
structure(list(Time = structure(c(6L, 6L, 6L, 6L, 6L, 6L, 6L,
6L, 6L, 6L), .Label = c("Friday", "Monday", "Saturday", "Sunday",
"Thursday", "Tuesday", "Wednesday"), class = "factor"), Viewers = c(5923L,
6006L, 6109L, 5925L, 5708L, 5829L, 5989L, 6007L, 5963L, 5980L
), day_of_year = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L), .Label = c("187", "188", "189", "190", "191", "192",
"193", "194", "195", "196", "197", "198", "199", "200", "201",
"202", "203", "204", "205", "206", "207", "208", "209", "210",
"211", "212", "213"), class = "factor")), .Names = c("Time",
"Viewers", "day_of_year"), class = c("data.table", "data.frame"
), row.names = c(NA, -10L), .internal.selfref = <pointer: 0x0000000000340788>)
我还在我的Rmd文档中添加了library(dplyr)和library(plyr)，错误更改为：
Quitting from lines 330-346 (index.Rmd)
Error in which(!as.logical(j)) :
(list) object cannot be coerced to type 'logical'
Calls: <Anonymous> ... withCallingHandlers -> withVisible -> eval -> eval -> [ -> [.xts -> which
Execution halted