条件算术运算错误信息

Question

在我的数据框中，我想通过将 DiscVar 变量乘以一个数字（1400、(1400-342)，或 (1400+500))，具体取决于产品。

只有第一次运算才算出来的问题，即dfq$DiscVar * 1400，我也不知道为什么。

感谢您的帮助！！

# Data & arithmetic operation  
dfq <- data.frame(ObjVar=c("hat","hat","shoe","shoe","umbrella"),DiscVar=c(0.19,0.39,0.18,1.00,0.64))
dfq$CostVar[dfq$ObjVar == "hat"] <- dfq$DiscVar * 1400
dfq$CostVar[dfq$ObjVar == "shoe"] <- dfq$DiscVar * (1400-342)
dfq$CostVar[dfq$ObjVar == "umbrella"] <- dfq$DiscVar * (1400+500)

Answer 1

您对结果进行了子集化，但忘记了对操作数进行子集化。

dfq <- data.frame(ObjVar=c("hat","hat","shoe","shoe","umbrella"),DiscVar=c(0.19,0.39,0.18,1.00,0.64))

dfq$CostVar <- 0    # First, create the entire new column
dfq$CostVar[dfq$ObjVar == "hat"] <- dfq$DiscVar[dfq$ObjVar == "hat"] * 1400
dfq$CostVar[dfq$ObjVar == "shoe"] <- dfq$DiscVar[dfq$ObjVar == "shoe"] * (1400-342)
dfq$CostVar[dfq$ObjVar == "umbrella"] <- dfq$DiscVar[dfq$ObjVar == "umbrella"] * (1400+500)

Answer 2

如果唯一元素比较多，我们可以创建一个命名的vector来匹配'ObjVar'中的元素，然后做算术

nm1 <- setNames(c(1400, 1400-342, 1400 + 500), c('hat', 'shoe', 'umbrella'))
dfq$CostVar <- with(dfq, nm1[ObjVar] * DiscVar)

条件算术运算错误信息

conditional arithmetic operation error message

r

arithmetic-expressions