我需要添加一个均值，方差和标准偏差列（每个主题），但我的数据有点复杂：
我有主题ID，日期＆amp;时间，一年中的几周，总体出勤人数和每周的出勤率。现在我需要的是另外3列，给我每周的平均访问量，出勤率和标准差。
为了更清楚，这是我的数据集的快照：
df <- c(Contact.ID, Date.Time, Week, Attendance, WeeklyAT)
Contact.ID Date Time Week Attendance WeeklyAT *Mean *v *sd
1 A 2012-10-06 18:54:48 40 3 2 *0.214 *0.335 *0.579
2 A 2012-10-08 20:50:18 40 3 2 *0.214 *0.335 *0.579
3 A 2012-11-24 20:18:44 47 3 1 *0.214 *0.335 *0.579
4 B 2012-11-15 16:58:15 46 4 1
5 B 2013-01-09 10:57:02 2 4 3
6 B 2013-01-11 17:31:22 2 4 3
7 B 2013-01-14 18:37:00 2 4 3
8 C 2013-02-22 17:46:07 8 2 1
9 C 2013-02-27 11:21:00 9 2 1
10 D 2012-10-28 14:48:33 43 1 1
要计算平均出勤率，需要考虑的是，我正在查看的时间范围为14周，并且每周出勤率都会重复，因此需要与周数绑定。因此，要计算主题A和B的意思，例如它必须是：
meanA =（2 + 1 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0）/14=0.214
meanB =（1 + 3 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0）/14=0.286
（这里14周并不重要，但是对于方差和sd它确实如此：
方差A =Σ（x-μ）^ 2 = [（2-0.214）^ 2 +（1-0.214）^ 2 +（0-0.214）^ 2 +（0-0.214）^ 2 +（0- 0.214）^ 2 +（0-0.214）^ 2 +（0-0.214）^ 2 +（0-0.214）^ 2 +（0-0.214）^ 2 +（0-0.214）^ 2 +（0-0.214） ^ 2 +（0-0.214）^ 2 +（0-0.214）^ 2 +（0-0.214）^ 2] /（14-1）= 4.357 / 13 = 0.335
sdA =√varianceA=√0.335= 0.579
我无法弄清楚如何在代码中执行此操作。我尝试了ifelse个函数和一般var和mean，并尝试使用这些函数创建新列但未能按主题（Contact.ID）和我的n = 14定义它。< / p>
我非常感谢帮助。非常感谢！
答案 0 :(得分：1)
这是一个非常粗略的解决方案（需要去）。我假设原始问题中的计算并不完全正确，如果我错了，你应该能够调整我的代码：
编辑1：更新代码 - 因为方差计算中使用的均值错误并添加了一些注释。
# Set to data.table
setDT(df)
# Number of weeks in our data
nweeks <- df[, uniqueN(Week)] # 7
# Calculate mean number of visits per week
df[, Mean := .N / nweeks, by = .(Contact.ID)]
# Add the rank of the week, this variable is used in the loop below
df <- merge(df,
df[!duplicated(Week), .(Week, num_week = rank(Week))])
# Set key for tha data.table... makes syntax simpler
setkey(df, Contact.ID, num_week)
# Initalize variance variable
df[, v := 0]
# For each id go through every week and fill in vector of number of visits
# attendance_vector based on which we will calculate variance for each id.
for (id in unique(df$Contact.ID)) {
attendance_vector <- integer(nweeks)
mean <- df[id, Mean][1] # mean for this id...
for (week in unique(df$num_week)) {
attendance_vector[week] <-
df[.(id, week)][1, ifelse(!is.na(WeeklyAT), WeeklyAT, 0)]
}
df[id, v := sum((attendance_vector - mean)^2) / (nweeks - 1L)]
cat("for", id, "the weekly attendance was: \n")
print(cbind(unique(df$Week), attendance_vector, mean))
}
# Standard deviation
df[, sd := sqrt(v), by = Contact.ID]
# Drop num_week variable
df[, num_week := NULL]
df
Week Contact.ID Date Time Attendance WeeklyAT Mean v sd
1: 40 A 2012-10-06 18:54:48 3 2 0.4285714 0.6190476 0.7867958
2: 40 A 2012-10-08 20:50:18 3 2 0.4285714 0.6190476 0.7867958
3: 47 A 2012-11-24 20:18:44 3 1 0.4285714 0.6190476 0.7867958
4: 2 B 2013-01-09 10:57:02 4 3 0.5714286 1.2857143 1.1338934
5: 2 B 2013-01-11 17:31:22 4 3 0.5714286 1.2857143 1.1338934
6: 2 B 2013-01-14 18:37:00 4 3 0.5714286 1.2857143 1.1338934
7: 46 B 2012-11-15 16:58:15 4 1 0.5714286 1.2857143 1.1338934
8: 8 C 2013-02-22 17:46:07 2 1 0.2857143 0.2380952 0.4879500
9: 9 C 2013-02-27 11:21:00 2 1 0.2857143 0.2380952 0.4879500
10: 43 D 2012-10-28 14:48:33 1 1 0.1428571 0.1428571 0.3779645
答案 1 :(得分：1)
df <- structure(list(Contact.ID = 1:10, Date = c("A", "A", "A", "B",
"B", "B", "B", "C", "C", "D"), Time = c("2012-10-06 18:54:48",
"2012-10-08 20:50:18", "2012-11-24 20:18:44", "2012-11-15 16:58:15",
"2013-01-09 10:57:02", "2013-01-11 17:31:22", "2013-01-14 18:37:00",
"2013-02-22 17:46:07", "2013-02-27 11:21:00", "2012-10-28 14:48:33"
), Week = c(40L, 40L, 47L, 46L, 2L, 2L, 2L, 8L, 9L, 43L), Attendance = c(3L,
3L, 3L, 4L, 4L, 4L, 4L, 2L, 2L, 1L), WeeklyAT = c(2L, 2L, 1L,
1L, 3L, 3L, 3L, 1L, 1L, 1L)), .Names = c("Contact.ID", "Date",
"Time", "Week", "Attendance", "WeeklyAT"), row.names = c(NA,
-10L), class = c("data.table", "data.frame"))
library(tidyverse)
df1 <- df %>%
group_by(Date) %>%
nest(Week, WeeklyAT) %>% # nest relevant data
mutate(data = map(data, ~.x %>% filter(duplicated(Week)==F))) %>% # filter out duplicated Weeks
mutate(data = map(data, ~c(.x$WeeklyAT, rep(0, 14-length(.x$WeeklyAT))))) %>% # make WeeklyAT into 14-element vector
mutate(data = map(data, ~data.frame(Mean = mean(.x), sd = sd(.x), v = sd(.x)**2))) %>% # calculate statistics and save as data frame
unnest(data) %>% # unnest results
left_join(df, ., by="Date") # combine with original data frame
Contact.ID Date Time Week Attendance WeeklyAT Mean
1 1 A 2012-10-06 18:54:48 40 3 2 0.21428571
2 2 A 2012-10-08 20:50:18 40 3 2 0.21428571
3 3 A 2012-11-24 20:18:44 47 3 1 0.21428571
4 4 B 2012-11-15 16:58:15 46 4 1 0.28571429
5 5 B 2013-01-09 10:57:02 2 4 3 0.28571429
6 6 B 2013-01-11 17:31:22 2 4 3 0.28571429
7 7 B 2013-01-14 18:37:00 2 4 3 0.28571429
8 8 C 2013-02-22 17:46:07 8 2 1 0.14285714
9 9 C 2013-02-27 11:21:00 9 2 1 0.14285714
10 10 D 2012-10-28 14:48:33 43 1 1 0.07142857
sd v
1 0.5789342 0.33516484
2 0.5789342 0.33516484
3 0.5789342 0.33516484
4 0.8254203 0.68131868
5 0.8254203 0.68131868
6 0.8254203 0.68131868
7 0.8254203 0.68131868
8 0.3631365 0.13186813
9 0.3631365 0.13186813
10 0.2672612 0.07142857