fcase到多个输出

Question

假设以下 table：

data <- data.table(dummy=1:10)

我知道你可以做以下事情：

data[dummy < 5, c("test1", "test2") := list("Yes", 1)]

和：

data[, test1 := fcase(dummy < 5, "Yes")]
data[, test2 := fcase(dummy < 5, 1)]

我正在尝试将它们合二为一：

data[, c("test1", "test2") := fcase(dummy < 5, list("Yes", 1))]

但它给我以下错误：

Error in fcase(dummy < 5, list("Yes", 1)) : 
  Length of output value #2 must either be 1 or length of logical condition.

我需要通过多个过滤器，所以使用 fcase 很有意义。我总是可以像这样对每个过滤器使用第一个解决方案：

data[dummy < 5, c("test1", "test2") := list("Yes", 1)]
data[dummy > 7, c("test1", "test2") := list("No", 0)]
data[between(dummy, 5, 7), c("test1", "test2") := list("Maybe", NA)]

但我想知道是否还有更多可能。还有一个解决方案是用 test1 和 test2 的每个组合创建一个 table 并在执行 [=17= 之后将此 table 与数据 table 合并] 仅 test1 像这样：

tests <- data.table(test1 = c("Yes", "No", "Maybe"),
                    test2 = c(1, 0, NA))

data[, test1 := fcase(dummy < 5, "Yes",
                      dummy > 7, "No",
                      between(dummy, 5, 7), NA_character_)]
merge(data, tests, by = "test1", all.x = T, sort = F)

但这对于庞大而复杂的数据来说似乎效率低下table

Answer 1

与rbindlist:

data[, c("test1", "test2") := rbindlist(fcase(dummy < 5, .(.("Yes", 1)),
                                              dummy > 7, .(.("No", 0)),
                                              default = .(.("Maybe", NA))))]
data
#>     dummy test1 test2
#>  1:     1   Yes     1
#>  2:     2   Yes     1
#>  3:     3   Yes     1
#>  4:     4   Yes     1
#>  5:     5 Maybe    NA
#>  6:     6 Maybe    NA
#>  7:     7 Maybe    NA
#>  8:     8    No     0
#>  9:     9    No     0
#> 10:    10    No     0

do.call 将允许您将 fcase 条件放入一个列表中，并将值放入另一个嵌套列表列表中：

data[, c("test1", "test2") := rbindlist(do.call(fcase, rbind(.(dummy < 5, dummy <= 7, dummy > 7),
                                                             .(.(.("Yes", 1)), .(.("Maybe", NA)), .(.("No", 0))))))]

或者以 tests 为例：

tests <- data.table(test1 = c("Yes", "Maybe", "No"),
                    test2 = c(1, NA, 0))
tests[, val := .(.(.(.SD))), by = 1:nrow(tests)]
data[, c("test1", "test2") := rbindlist(do.call(fcase, rbind(.(dummy < 5, dummy <= 7, dummy > 7), tests$val)))]

fcase到多个输出

fcase to multiple outputs

r

case

data.table