转换为负数

Question

在这样的数据中：

data.frame (com = c("col1","em"), stock1 = c(2.6, 0), aim = c(0,3.10))

如何用com“ em”向行的所有行添加减号

预期结果示例：

data.frame (com = c("col1","em"), stock1 = c(2.6, 0), aim = c(0,-3.10))
   com stock1  aim
1 col1    2.6  0.0
2   em    0.0 -3.1

Answer 1

使用ifelse：

df1 <- data.frame (com = c("col1","em"), stock1 = c(2.6, 0), aim = c(0,3.10))

df1$aim <- ifelse(df1$com == "em", -df1$aim, df1$aim)

df1
   com stock1  aim
1 col1    2.6  0.0
2   em    0.0 -3.1

Answer 2

这是如何工作的？

xy <- data.frame (com = c("col1","em"), stock1 = c(2.6, 0), aim = c(0,3.10))

find.com <- -which(names(xy) == "com")
xy[xy$com == "em", find.com] <- -xy[xy$com == "em", find.com]
xy

   com stock1  aim
1 col1    2.6  0.0
2   em    0.0 -3.1