在 data.table 中分組后查找統計信息

Question

我有一個關於 data.table 的小問題。 因為我不太擅長它，所以我不太確定如何在 data.table 中做到這一點。

基本上我有 3 列，想按前兩列（鍵和日期）分組，然后對於每個鍵和每個日期，找到第三列（票價）中出現的最大值和最小值

我試過這樣做，但它給了我一個錯誤

flights[, c("max_day", "min_day") := unlist(lapply(gross_fare, findr)), by = c("key", "created_date")]

Error in `[.data.table`(flights, , `:=`(c("max_day", "min_day"), unlist(lapply(gross_fare,  : 
  Supplied 18 items to be assigned to group 1 of size 9 in column 'max_day'. The RHS length must either be 1 (single values are ok) or match the LHS length exactly. If you wish to 'recycle' the RHS please use rep() explicitly to make this intent clear to readers of your code.

findr 是一個函數，它只找到最大值和最小值，即

findr <- function(x) {list(max = max(x), min = min(x)}

我已經在 dplyr 中完成了我想做的事情，我會附上代碼，但是由於我有數百萬行，dplyr 吃光了我的內存，因此 data.table 會有所幫助

test <- flights %>%
  select(key, created_date, gross_fare) %>%
  group_by(key, created_date) %>%
  summarise(
            max_day = max(gross_fare),
            min_day = min(gross_fare),
            diff = max_day - min_day) %>%
  arrange(created_date)

如果有人想使用它，我已經把 dput 輸出放在那里，如果有人能提供幫助，那就太好了，謝謝:)

structure(list(key = c("LHE_KHI_LHE+KHI_PA-405_15.0_1", "KHI_ISB_KHI+ISB_PK-370_20.0_0", 
"LHE_KHI_LHE+KHI_PK-307_20.0_0", "ISB_KHI_ISB+KHI_PF-124_20.0_1", 
"LHE_KHI_LHE+KHI_PK-307_20.0_0", "LHE_KHI_LHE+KHI_PA-405_15.0_1", 
"KHI_LHE_KHI+LHE_PK-304_20.0_0", "KHI_ISB_KHI+ISB_PA-204_15.0_1", 
"ISB_KHI_ISB+KHI_PA-207_15.0_1", "KHI_ISB_KHI+ISB_PA-200_20.0_1", 
"KHI_LHE_KHI+LHE_PK-304_40.0_0", "ISB_KHI_ISB+KHI_PA-201_35.0_1", 
"ISB_KHI_ISB+KHI_ER-501_20.0_1", "KHI_LHE_KHI+LHE_PF-145_20.0_2", 
"KHI_ISB_KHI+ISB_PA-204_20.0_1", "LHE_KHI_LHE+KHI_PA-401_0.0_0", 
"ISB_KHI_ISB+KHI_PK-309_40.0_0", "KHI_ISB_KHI+ISB_PF-123_20.0_2", 
"ISB_KHI_ISB+KHI_PA-205_15.0_1", "LHE_KHI_LHE+KHI_PF-142_0.0_0", 
"ISB_KHI_ISB+KHI_PA-223_15.0_1", "ISB_KHI_ISB+KHI_PF-126_20.0_2", 
"ISB_KHI_ISB+KHI_PK-309_20.0_0", "KHI_ISB_KHI+ISB_PF-121_20.0_2", 
"ISB_KHI_ISB+KHI_PK-373_20.0_0", "KHI_LHE_KHI+LHE_PF-145_20.0_2", 
"KHI_LHE_KHI+LHE_PA-402_15.0_1", "LHE_KHI_LHE+KHI_PA-407_20.0_1", 
"KHI_ISB_KHI+ISB_PK-308_40.0_0", "KHI_LHE_KHI+LHE_PF-145_20.0_2", 
"LHE_KHI_LHE+KHI_PF-144_0.0_0", "ISB_KHI_ISB+KHI_PK-369_40.0_0", 
"ISB_KHI_ISB+KHI_PF-124_20.0_2", "KHI_ISB_KHI+ISB_PA-204_15.0_1", 
"KHI_ISB_KHI+ISB_PA-200_15.0_1", "ISB_KHI_ISB+KHI_PF-124_20.0_1", 
"KHI_ISB_KHI+ISB_PK-300_20.0_0", "ISB_KHI_ISB+KHI_PF-122_20.0_2", 
"KHI_ISB_KHI+ISB_PK-368_20.0_0", "KHI_ISB_KHI+ISB_PA-204_15.0_1", 
"ISB_KHI_ISB+KHI_ER-503_20.0_1", "ISB_KHI_ISB+KHI_PA-209_15.0_1", 
"KHI_ISB_KHI+ISB_PK-308_40.0_0", "ISB_KHI_ISB+KHI_PF-124_20.0_1", 
"ISB_KHI_ISB+KHI_PK-301_40.0_0", "KHI_LHE_KHI+LHE_PA-408_35.0_1", 
"LHE_KHI_LHE+KHI_PF-144_20.0_2", "KHI_ISB_KHI+ISB_PF-121_20.0_2", 
"KHI_ISB_KHI+ISB_PA-204_35.0_1", "ISB_KHI_ISB+KHI_PK-309_40.0_0", 
"ISB_KHI_ISB+KHI_PA-223_20.0_1", "KHI_ISB_KHI+ISB_PA-206_35.0_1", 
"LHE_KHI_LHE+KHI_PF-142_32.0_1", "LHE_KHI_LHE+KHI_PF-142_20.0_1", 
"KHI_ISB_KHI+ISB_PF-123_20.0_2", "ISB_KHI_ISB+KHI_PA-209_15.0_1", 
"KHI_ISB_KHI+ISB_PA-204_35.0_1", "ISB_KHI_ISB+KHI_PA-201_20.0_1", 
"KHI_ISB_KHI+ISB_PK-368_20.0_0", "ISB_KHI_ISB+KHI_PA-205_20.0_1", 
"KHI_ISB_KHI+ISB_PF-121_20.0_1", "ISB_KHI_ISB+KHI_PF-124_20.0_1", 
"ISB_KHI_ISB+KHI_PA-205_15.0_1", "KHI_LHE_KHI+LHE_PF-145_20.0_2", 
"KHI_LHE_KHI+LHE_PA-406_35.0_1", "KHI_ISB_KHI+ISB_PK-308_20.0_0", 
"LHE_KHI_LHE+KHI_PA-401_20.0_1", "LHE_KHI_LHE+KHI_PA-401_15.0_1", 
"KHI_ISB_KHI+ISB_PA-204_35.0_1", "KHI_LHE_KHI+LHE_PA-406_35.0_1", 
"KHI_ISB_KHI+ISB_PA-206_35.0_1", "KHI_ISB_KHI+ISB_PF-121_20.0_1", 
"ISB_KHI_ISB+KHI_PA-205_20.0_1", "LHE_KHI_LHE+KHI_PF-142_20.0_1", 
"LHE_KHI_LHE+KHI_PF-146_20.0_2", "LHE_KHI_LHE+KHI_PA-401_35.0_1", 
"ISB_KHI_ISB+KHI_PA-209_15.0_1", "ISB_KHI_ISB+KHI_PK-301_40.0_0", 
"ISB_KHI_ISB+KHI_PA-205_35.0_1", "KHI_LHE_KHI+LHE_PA-406_15.0_1", 
"KHI_ISB_KHI+ISB_PF-123_20.0_1", "ISB_KHI_ISB+KHI_PA-201_35.0_1", 
"KHI_ISB_KHI+ISB_PK-300_40.0_0", "KHI_LHE_KHI+LHE_PA-402_35.0_1", 
"ISB_KHI_ISB+KHI_ER-505_20.0_1", "ISB_KHI_ISB+KHI_PF-122_20.0_2", 
"ISB_KHI_ISB+KHI_PA-207_15.0_1", "KHI_LHE_KHI+LHE_PA-404_35.0_1", 
"KHI_ISB_KHI+ISB_PF-123_20.0_1", "ISB_KHI_ISB+KHI_ER-503_20.0_1", 
"ISB_GIL_ISB+GIL_PK-605_20.0_0", "KHI_ISB_KHI+ISB_PF-123_20.0_1", 
"KHI_ISB_KHI+ISB_PA-200_15.0_1", "ISB_KHI_ISB+KHI_PF-122_20.0_2", 
"KHI_LHE_KHI+LHE_PA-404_35.0_1", "ISB_KHI_ISB+KHI_PF-122_20.0_2", 
"PEW_KHI_PEW+KHI_PF-152_20.0_1", "LHE_KHI_LHE+KHI_PK-303_20.0_0", 
"KHI_ISB_KHI+ISB_PA-222_35.0_1", "ISB_KHI_ISB+KHI_PF-124_20.0_1"
), created_date = c("2021-04-20", "2021-05-27", "2021-02-13", 
"2021-08-14", "2021-08-11", "2021-08-21", "2021-01-26", "2021-08-21", 
"2021-05-24", "2021-09-15", "2021-06-05", "2021-07-19", "2021-09-29", 
"2021-07-02", "2021-08-10", "2021-01-04", "2021-07-15", "2021-07-14", 
"2021-08-13", "2021-01-11", "2021-09-13", "2021-09-20", "2021-05-27", 
"2021-02-20", "2021-08-15", "2021-07-27", "2021-08-26", "2021-09-15", 
"2021-08-02", "2021-06-25", "2021-05-15", "2021-08-26", "2021-07-30",
"2021-06-27", "2021-08-07", "2021-03-19", "2021-03-02", "2021-06-06", 
"2021-08-15", "2021-06-27", "2021-09-19", "2021-07-28", "2021-08-09", 
"2021-08-16", "2021-09-09", "2021-06-04", "2021-08-12", "2021-05-15", 
"2021-07-26", "2021-05-27", "2021-08-12", "2021-08-02", "2021-01-26", 
"2021-04-20", "2021-08-26", "2021-08-26", "2021-03-21", "2021-01-09", 
"2021-04-23", "2021-01-04", "2021-08-13", "2021-06-22", "2021-05-31", 
"2021-08-18", "2021-06-16", "2021-08-14", "2021-08-10", "2021-06-16", 
"2021-04-08", "2021-05-20", "2021-06-22", "2021-04-20", "2021-01-05", 
"2021-02-27", "2021-07-07", "2021-03-26", "2021-08-16", "2021-05-01", 
"2021-07-31", "2021-06-14", "2021-06-16", "2021-03-25", "2021-09-14", 
"2021-06-06", "2021-09-02", "2021-08-06", "2021-07-18", "2021-02-28", 
"2021-04-28", "2021-09-19", "2021-08-25", "2021-06-17", "2021-06-07", 
"2021-06-17", "2021-07-07", "2021-08-23", "2021-07-09", "2021-07-19", 
"2021-07-14", "2021-05-21"), gross_fare = c(7796, 7427, 11504, 
6870, 6580, 14945, 8697, 7524, 7124, 6785, 11858, 7524, 11500, 
9525, 6785, 8739, 8200, 13560, 9045, 7400, 7524, 12500, 7458, 
14000, 6570, 9525, 6220, 10545, 8310, 7900, 7820, 8410, 11285, 
19892, 6810, 9800, 11441, 11900, 6570, 13592, 11500, 8300, 20380, 
8525, 7340, 9707, 7870, 10655, 10545, 11798, 14645, 10545, 8650, 
8650, 7870, 12945, 10799, 10227, 6765, 10227, 20120, 11045, 9403, 
7870, 7124, 6570, 6810, 6531, 8605, 7124, 11072, 7390, 10227, 
13435, 10530, 12280, 18945, 11147, 10545, 6531, 6620, 10799, 
18480, 32702, 5606, 13560, 23895, 8027, 9655, 11500, 11990, 6620, 
9403, 7620, 14645, 19105, 9000, 6440, 12645, 8025)), row.names = c(NA, 
-100L), class = c("data.table", "data.frame"), .internal.selfref = <pointer: 0x000001eb382c1ef0>)
> 

Answer 1

我想這行代碼應該可以完成這項工作：

library(data.table)

flights[,  .(min_day = min(gross_fare), max_day = max(gross_fare), diff = max(gross_fare) - min(gross_fare)), by = .(key, created_date)][]

Answer 2

由於函數findr返回一個列表，因此無需將事情復雜化：

findr <- function(x) {list(max = max(x), min = min(x))}

flights[, c("max_day", "min_day") := findr(gross_fare), by = list(key, created_date)][]

要同時返回max和min之間的差異，請使用

findr2 <- function(x) {
  list(max = max(x), min = min(x), diff = diff(range(x)))
}

flights[, c("max_day", "min_day", "diff_day") := findr2(gross_fare), by = list(key, created_date)][]