R 如何根据另一列中某个值的单个出现，使一列中的所有值相同？

因此，我有一个数据框架，其中有a-E中的物种名称和等级归属于每个物种，有时会出现具有不同等级的相同物种，但我想要以下信息： 如果一个物种甚至有一次出现在X级，那么该物种的所有其他出现也必须是X级。这是我的数据框：

     species        |    grade      | 
-----------------------------------
Tilapia guineensis  | B |
Tilapia guineensis  | E |
Tilapia zillii      | A |
Fundulus rubrifrons | A |
Eutrigla gurnardus  | D |
Sprattus sprattus   | A |
Gadus morhua        | E |
Gadus morhua        | B |
Tilapia zillii      | C |
Gadus morhua        | B | 
Eutrigla gurnardus  | C |

到目前为止，我以E级为例尝试了以下方法：

 df<-df%>% left_join(df%>% 
                                   group_by(species) %>% 
                                   summarize(sum_e = sum(grade=='E')),by='species') %>%
    mutate(grade = ifelse(sum_e>0,"E",grade))

我想要的输出基本上是这样的：

     species        |    grade      | 
-----------------------------------
Tilapia guineensis  | E |
Tilapia guineensis  | E |
Tilapia zillii      | C |
Fundulus rubrifrons | A |
Eutrigla gurnardus  | D |
Sprattus sprattus   | A |
Gadus morhua        | E |
Gadus morhua        | E |
Tilapia zillii      | C |
Gadus morhua        | B | 
Eutrigla gurnardus  | D |

---

下面是我将如何使用

data.table

package来实现这一点。我认为如果更改为

dplyr

的话，阶段会相似，只是写得不同而已

# solution using data.table package
library(data.table)

# fake data, replace with yours
df <- data.frame(species=c("a", "a", "b", "b"),
                 grade=c("A", "E", "B", "C"))

# select your grade
dominant_grade <- "E"
# convert to data.table
dt <- as.data.table(df)
# search over species, add a column that checks if any of the grades is equal
# to the dominant one
dt[, contains_dominant := any(grade == dominant_grade), by=species]
# For cases where the dominant one is present, set all the grades to the dominant
# one
dt[contains_dominant == TRUE, grade := dominant_grade]

# convert back to data frame and trim for output
out <- setDF(dt[, .(species, grade)])
out

#使用data.table包的解决方案
库（数据表）
#伪造数据，替换为您的数据
df谢谢，我认为这是有效的！但接下来，我该如何更新这个代码：“哦，对了，你可以使用
out为什么
zillii罗非鱼的等级从
a，C
改为
C，C
？
# solution using data.table package
library(data.table)

# fake data, replace with yours
df <- data.frame(species=c("a", "a", "b", "b"),
                 grade=c("A", "E", "B", "C"))

# select your grade
dominant_grade <- "E"
# convert to data.table
dt <- as.data.table(df)
# search over species, add a column that checks if any of the grades is equal
# to the dominant one
dt[, contains_dominant := any(grade == dominant_grade), by=species]
# For cases where the dominant one is present, set all the grades to the dominant
# one
dt[contains_dominant == TRUE, grade := dominant_grade]

# convert back to data frame and trim for output
out <- setDF(dt[, .(species, grade)])
out