Question

我有以下data.frame

qs <- structure(list(Question = c("This is a question", "This is a question"), 
Correct_Answer = c("D", "B"), 
Answer.A = c("This is an answer", "This is an answer"), 
Answer.B = c("This is an answer", "This is an answer"), 
Answer.C = c("This is an answer", "This is an answer"), 
Answer.D = c("This is an answer", "This is an answer"), 
Explanation = c("Just because!", "Just because!"), 
Response_A = c("", ""), 
Response_B = c("", ""), 
Response_C = c("", ""), 
Response_D = c("", "")), 
.Names = c("Question", "Correct_Answer", "Answer.A", "Answer.B",
           "Answer.C", "Answer.D", "Explanation", "Response_A", 
           "Response_B", "Response_C", "Response_D"), 
row.names = 1:2, class = "data.frame")

我想设置Response_X值以匹配每个问题的Explanation。例如，在第一行中，Correct_Answer是D，因此Response_D应该等于解释，另一个Responses_应该保持空白。

我尝试过以下方法：

library(dplyr)

qs %>% rowwise() %>% mutate_(.dots=setNames(paste(Explanation), 
                          paste0("Response_",Correct_Answer)))

它给出了：

Error in paste0("Response_", Correct_Answer) : 
  object 'Correct_Answer' not found

我觉得我应该在这里使用申请，但不确定如何。

Answer 1

一种方法是使用自定义函数，该函数在该行的正确列中指定正确的值

assignValue <- function(x) {
   qs[x, paste0("Response_", qs$Correct_Answer[x])] <<- qs$Explanation[x]
 }

然后使用sapply

为每一行调用该函数

sapply(1:nrow(qs), function(x) assignValue(x))

注意，在函数中使用<<-运算符。从帮助页面（?"<<-"）

运营商＆lt;＆lt; - ＆ - ＆gt;＆gt;通常仅在函数中使用，并且通过父环境搜索要分配的变量的现有定义。如果找到这样的变量（并且它的绑定没有被锁定），那么它的值被重新定义，否则赋值发生在全局环境中

Answer 2

tidyverse解决方案。您将数据收集到＆＃34; tidy＆＃34;形式，在Correct_Answer上有条件地变异，并将其展开。

library(tidyr)
library(dplyr)

qs %>% 
   gather(Resp, val, Response_A:Response_D, -Correct_Answer, -Explanation) %>% select(-val) %>% 
   mutate(Expl = if_else(paste("Response", Correct_Answer, sep="_") == Resp, Explanation, "")) %>%
   spread(Resp, Expl)

希望这样做！

Answer 3

使用常规for循环你可以这样做：

for(i in 1:nrow(qs)){
    qs[i,paste('Response_',qs[i,'Correct_Answer'], sep = '')]=qs[i,'Explanation']
}

我仍然试图找出如何使用sapply更新col值。

sapply(1:nrow(qs), function(i) qs[paste('Response_',qs[i,'Correct_Answer'], sep = '')]=qs[i,'Explanation'])

在dplyr

3 个答案: