r - 将 case_when 与 dplyr 一起使用

Question

我正在尝试使用 dplyr 的新“跨”函数将 mutate_at() 转换为 mutate() 并且有点难倒。
简而言之，我需要将一系列列中的值与“基线”列进行比较。当列中的值高于基线时，我需要使用基线值。当列中的值低于或等于基线时，我需要保留该值。这是一个示例数据集(我的实际数据集要大得多):

test <- structure(list(baseline = c(5, 7, 8, 4, 9, 1, 0, 46, 47), bob = c(7, 
11, 34, 9, 6, 8, 3, 49, 12), sally = c(3, 5, 2, 2, 6, 1, 3, 4, 
56), rita = c(6, 4, 6, 7, 6, 0, 3, 11, 3)), class = c("spec_tbl_df", 
"tbl_df", "tbl", "data.frame"), row.names = c(NA, -9L), spec = structure(list(
    cols = list(baseline = structure(list(), class = c("collector_double", 
    "collector")), bob = structure(list(), class = c("collector_double", 
    "collector")), sally = structure(list(), class = c("collector_double", 
    "collector")), rita = structure(list(), class = c("collector_double", 
    "collector"))), default = structure(list(), class = c("collector_guess", 
    "collector")), skip = 1), class = "col_spec"))

我当前的代码使用 mutate_at() 并且工作正常:

trial1 <- test %>% 
  mutate_at(
    vars('bob','sally', 'rita'),
    funs(case_when(
      . > baseline ~ baseline, 
      . <= baseline ~ .)))

但是当我尝试更新它以反射(reflect) dplyr 1.0 的cross() 时，我不断收到错误消息。这是我的尝试:

trial2 <- test %>% 
  mutate(across(c(bob, sally, rita), 
                case_when(. > baseline ~ baseline, 
                          . <= baseline ~ .)))

这是错误:

error: Problem with mutate() input ..1.x . > baseline ~ baseline, . <= baseline ~ . must be length 36 or one, not 9, 4.ℹ Input ..1 is across(...)

任何想法我可能做错了什么？ case_when() 是否适用于cross？

Answer 1

我们可以使用 ~指定匿名函数/lambda 函数调用

library(dplyr)
test %>% 
   mutate(across(c(bob, sally, rita), 
             ~ case_when(. > baseline ~ baseline, 
                       . <= baseline ~ .)))

-输出

# A tibble: 9 x 4
#  baseline   bob sally  rita
#     <dbl> <dbl> <dbl> <dbl>
#1        5     5     3     5
#2        7     7     5     4
#3        8     8     2     6
#4        4     4     2     4
#5        9     6     6     6
#6        1     1     1     0
#7        0     0     0     0
#8       46    46     4    11
#9       47    12    47     3

或与 .funs争论

test %>% 
        mutate(across(c(bob, sally, rita), 
                  .funs = case_when(. > baseline ~ baseline, 
                            . <= baseline ~ .)))

根据 ?across fns 的参数可以是

Functions to apply to each of the selected columns. Possible values are:

NULL, to returns the columns untransformed.

A function, e.g. mean.

A purrr-style lambda, e.g. ~ mean(.x, na.rm = TRUE)

A list of functions/lambdas, e.g. list(mean = mean, n_miss = ~ sum(is.na(.x))

此外，而不是 case_when ，我们可以利用 pmin

test %>% 
    mutate(across(c(bob, sally, rita), ~ pmin(baseline, .)))

-输出

# A tibble: 9 x 4
#  baseline   bob sally  rita
#     <dbl> <dbl> <dbl> <dbl>
#1        5     5     3     5
#2        7     7     5     4
#3        8     8     2     6
#4        4     4     2     4
#5        9     6     6     6
#6        1     1     1     0
#7        0     0     0     0
#8       46    46     4    11
#9       47    12    47     3