r - 我正在比较两列以创建第三列...它不起作用？

Question

这绝对是一个新手问题，但我被卡住了，无法在网上找到类似的帮助。我正在尝试比较数据框的两列以创建第三列。这是我想比较 Distx 和 Disty 的 mydf。如果其中任何一个都有值，我想保留它并将其放在新的 Distz 列中。如果它们都是“Missing”，我想将“Missing”放在 Distz 中。以下是我想要获取的数据框。

    ID <- c(1, 2, 3, 4, 5, 6)
    Distx <- c("A", "B", "Missing", "Missing", "G", "Missing")
    Disty <- c("Missing", "Missing", "C", "Missing", "Missing", "E")

    mydf <- data.frame(ID, Distx, Disty, Distz) 
    mydf

     ID   Distx   Disty   Distz
    1  1       A Missing       A
    2  2       B Missing       B
    3  3 Missing       C       C
    4  4 Missing Missing Missing
    5  5       G Missing       G
    6  6 Missing       E       E

这是不起作用的代码...起初我以为我没有正确索引，但是下面的第二次代码尝试结果相同..没有错误消息但结果是 1，而不是列的实际值....?

    for (i in seq(1:nrow(mydf))){
       if (mydf$Distx[i] == "Missing" && mydf$Disty[i] != "Missing"){
         mydf$Distz[i]<- mydf$Disty[i]}
       if (mydf$Distx[i] != "Missing" && mydf$Disty[i] == "Missing"){
        mydf$Distz[i]<- mydf$Distx[i]}
       if (mydf$Distx[i] == "Missing" && mydf$Disty[i] == "Missing"){
        mydf$Distz[i]<- "Missing"}
    }

    #for the purposes of readability I only ran two of the tests in this code
    within(mydf, {
      Distz <- ifelse(Distx == "Missing" & Disty != "Missing", Disty,          ifelse(Distx != "Missing" & Disty == "Missing", Distx))
    })

    #Both results look like this ...???

      ID   Distx   Disty Distz
    1  1       A Missing     1
    2  2       B Missing     1
    3  3 Missing       C     1
    4  4 Missing Missing     1
    5  5       G Missing     1
    6  6 Missing       E     1

在此先感谢您的帮助

Answer 1

您可以尝试嵌套的 ifelse 语句:

mydf$Distz <- with(mydf, ifelse(Distx == "Missing" & Disty == "Missing", "Missing", 
                           ifelse(Distx != "Missing", as.character(Distx), 
                             ifelse(Disty != "Missing", as.character(Disty), NA))))
mydf
#   ID   Distx   Disty   Distz
# 1  1       A Missing       A
# 2  2       B Missing       B
# 3  3 Missing       C       C
# 4  4 Missing Missing Missing
# 5  5       G Missing       G
# 6  6 Missing       E       E

您在代码中遇到的问题是您的变量是“因子”类，而不是“字符”类，因此代码记录的是因子“水平”而不是因子标签。这在上面通过使用 as.character() 将因子强制转换为字符来解决。