fcase 到多个输出

Question

假设如下表：

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)]

我正在尝试将这些组合成一个，如下所示：

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

但它给了我以下错误：

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

我需要经过多个过滤器，所以使用fcase. 我总是可以对每个过滤器使用第一个解决方案，如下所示：

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其他可能。还有一种解决方案，即使用test1和的每种组合创建一个表，并在执行for 仅test2之后将此表与数据表合并，如下所示：fcasetest1

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)

但这对于大型且复杂的数据表来说似乎效率低下

Answer 1

和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可以让您将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))))))]

或者用这个tests例子：

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)))]