摘要 table 一些列对 R 中带有变量的向量求和

Question

我有一个 table 看起来像这样：

    df <- data.frame(week = c("one","one","two","two"),
                     Day = c("day1", "day2","day1","day2"),
                     daily_freq = c(100,110,90,90),
                     city1 = c(20,30,20,30),
                     city2 = c(10,20,30,40),
                     city3 = c(30,40,10,10),
                     city4 = c(40,20,30,10))

我正在计算几个摘要 table，例如，一个 table 具有那个时期的总频率：

resume_table <- setDT(df)[, .( total_freq = sum(daily_freq),
                               city1 = sum(city1),
                               city2 = sum(city2),
                               city3 = sum(city3),
                               city4 = sum(city4))
                                       ,by = .(week)]

找到总频率如下所示的 table：

    week  total_freq city1 city2 city3 city4
    one        210    50    30    70    60
    two        180    50    70    20    40

但是因为我有几个城市（超过40个），我需要计算几个摘要tables，我想有，例如，一个包含城市的向量：

      cities <- c("city1","city2","city3","city4")

并且每次我对这个向量变量求和并仍然对其他列求和时，都能够调用这个向量。我的代码不起作用：

resume_table2 <- setDT(df)[, .(total_freq = sum(daily_freq),
                     lapply(.SD, sum), .SDcols = cities)
                               ,by = .(week)]

怎么了？

Answer 1

我们可以在 .SDcols 中指定 'cities' 向量并循环遍历 .SD 以获得 sum

setDT(df)[, lapply(.SD, sum), .SDcols = cities]
#   city1 city2 city3 city4
#1:   105   100    55    65

如果我们还需要 'daily_freq'，则与 'cities'

连接

setDT(df)[, lapply(.SD, sum), .SDcols = c('daily_freq', cities)]
#    daily_freq city1 city2 city3 city4
#1:        325   105   100    55    65

摘要 table 一些列对 R 中带有变量的向量求和

Summary table with some columns summing over a vector with variables in R

variables

r

summary

vector