根据列的值从其他列获取值

对于数据框中的每一行，我想根据第三列中的值将值从一列复制到另一列。

我尝试使用组合的 for 循环和 if 函数来做到这一点：

    ## example

condition <- c("1","2","2","1","2","","3","3")
SZ01 <- c("1","1","1","1","1","","1","1")
SZ02 <- c("2","2","2","2","2","","2","2")
SZ03 <- c("3","3","3","3","3","","3","3")


df <- data.frame(cbind(condition,SZ01,SZ02,SZ03), stringsAsFactors = FALSE)


df$retribution <- NULL
df$special_prevention <- NULL
df$general_prevention <- NULL


for (i in 1:length(df$condition)){ 

  if (df$condition[i] == 1){

    df$retribution[i] <- df$SZ01[i]
    df$special_prevention[i] <- df$SZ02[i]
    df$general_prevention[i] <- df$SZ03[i]


  }else if (df$condition[i] == 2) {

    df$retribution[i] <- df$SZ02[i]
    df$special_prevention[i] <- df$SZ03[i]
    df$general_prevention[i] <- df$SZ01[i]

  }else if (df$condition[i] == 3) {

    df$retribution[i] <- df$SZ03[i]
    df$special_prevention[i] <- df$SZ01[i]
    df$general_prevention[i] <- df$SZ02[i]

  } else {
    df$retribution[i] <- "missing_condition"
    df$special_prevention[i] <- "missing_condition"
    df$general_prevention[i] <- "missing_condition"

  }
}

这似乎有效（没有错误消息），但是查看我的数据肯定有问题。

例如第 1 行有condition == 1。这意味着，对于这一行df$retribution应收到与第 1 行中的值相同的值df$SZ01.

但事实并非如此。有人可以看到我犯的错误吗？

请尝试以下操作：

condition <- c("1","2","2","1","2","","3","3")
SZ01 <- c("1","1","1","1","1","","1","1")
SZ02 <- c("2","2","2","2","2","","2","2")
SZ03 <- c("3","3","3","3","3","","3","3")


df <- data.frame(cbind(condition,SZ01,SZ02,SZ03), stringsAsFactors = F)

df$retribution <- ifelse(df$condition == "1", df$SZ01,
                         ifelse(df$condition == "2", df$SZ02,
                            ifelse(df$condition == "3", df$SZ03, "missing")))

df$special_prevention <- ifelse(df$condition == "1", df$SZ02, 
                                ifelse(df$condition == "2", df$SZ03,
                                       ifelse(df$condition == "3", df$SZ01, "missing")))

df$general_prevention <- ifelse(df$condition == "1", df$SZ03, 
                                ifelse(df$condition == "2", df$SZ01,
                                       ifelse(df$condition == "3", df$SZ02, "missing"))))

Output:

df
  condition SZ01 SZ02 SZ03 retribution special_prevention general_prevention
1         1    1    2    3           1                  2                  3
2         2    1    2    3           2                  3                  1
3         2    1    2    3           2                  3                  1
4         1    1    2    3           1                  2                  3
5         2    1    2    3           2                  3                  1
6                              missing            missing            missing
7         3    1    2    3           3                  1                  2
8         3    1    2    3           3                  1                  2