使用dplyr进行group_by并仅使用if（不包含else）语句进行条件变异 [英] Using dplyr to group_by and conditionally mutate only with if (without else) statement

问题描述

我有一个数据框，我需要按列条目进行分组，以便仅使用if语句（不包含else条件）有条件地对几个列进行突变。

I have a dataframe that I need to group by a combination of columns entries in order to conditionally mutate several columns using only an if statement (without an else condition).

更具体地说，如果某个组的列值超过预定义的阈值，我想对其求和，否则这些值应保持不变。

More specifically, I want to sum up the column values of a certain group if they cross a pre-defined threshold, otherwise the values should remain unchanged.

我有尝试同时使用 if_else 和 case_when 来执行此操作，但是这些函数需要使用 false参数（ if_else ）或默认情况下设置与NA不匹配的值（ case_when ）：

I have tried doing this using both if_else and case_when but these functions require either a "false" argument (if_else) or by default set values that are not matched to NA (case_when):

iris_mutated <- iris %>%
  dplyr::group_by(Species) %>%
  dplyr::mutate(Sepal.Length=if_else(sum(Sepal.Length)>250, sum(Sepal.Length)),
                Sepal.Width=if_else(sum(Sepal.Width)>170, sum(Sepal.Width)),
                Petal.Length=if_else(sum(Petal.Length)>70, sum(Petal.Length)),
                Petal.Width=if_else(sum(Petal.Width)>15, sum(Petal.Width)))

iris_mutated <- iris %>%
  dplyr::group_by(Species) %>%
  dplyr::mutate(Sepal.Length=case_when(sum(Sepal.Length)>250 ~ sum(Sepal.Length)),
                Sepal.Width=case_when(sum(Sepal.Width)>170 ~ sum(Sepal.Width)),
                Petal.Length=case_when(sum(Petal.Length)>70 ~ sum(Petal.Length)),
                Petal.Width=case_when(sum(Petal.Width)>15 ~ sum(Petal.Width)))

有任何想法如何执行此操作吗？

Any ideas how to do this instead?

编辑：

这里是一个预期输出的示例。
所有物种分组条目的花瓣宽度总和为 setosa 12.3， virginica 101.3和 versicolor 66.3 。如果我要求此总和至少应为15以求和（否则应保留原始值），那么我希望得到以下输出（仅显示 Petal.Width和 Species列）：

Here is an example for the expected output. The sum of the petal width for all species-wise grouped entries is 12.3 for setosa, 101.3 for virginica and 66.3 for versicolor. If I require that this sum should be at least 15 for the values to be summed up (otherwise the original value should be kept), then I expect the following output (only showing the columns "Petal.Width" and "Species"):

Petal.Width    Species
1           0.2     setosa
2           0.2     setosa
3           0.2     setosa
4           0.2     setosa
5           0.2     setosa
6           0.4     setosa
7           0.3     setosa
8           0.2     setosa
9           0.2     setosa
10          0.1     setosa
#...#
50          0.2     setosa
51          66.3 versicolor
52          66.3 versicolor
53          66.3 versicolor
#...#
100         66.3 versicolor
101         101.3  virginica
102         101.3  virginica
103         101.3  virginica
#...#
150         101.3  virginica

推荐答案

我认为您在船尾这个吗？使用约翰尼的方法。当总和不大于临界值时，当您将原始值用作case_的一部分时，您应该不会出错...

I think you are after this? Using Johnny's method. You shouldn't hit an error when you use the original value as part of case_when in the case when the sum is not greater than the cutoff...

iris_mutated <- iris %>% 
  group_by(Species) %>% 
  mutate(Sepal.Length = case_when(sum(Sepal.Length) > 250 ~ sum(Sepal.Length),
                                   T ~ Sepal.Length),
         Sepal.Width = case_when(sum(Sepal.Width) > 170 ~ sum(Sepal.Width),
                                   T ~ Sepal.Width),
         Petal.Length = case_when(sum(Petal.Length) > 70 ~ sum(Petal.Length),
                                   T ~ Petal.Length),
         Petal.Width = case_when(sum(Petal.Width) > 15 ~ sum(Petal.Width),
                                   T ~ Petal.Width))

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