根据第三列上的条件，将数据框中的值替换为另一列中的值 [英] Replace a value in a dataframe with a value in another column, based on a condition on a third column

问题描述

我的数据框：

class     columnA

foo       10
bar       14.2
hello     48695
bar       4
foo       -7

我试着执行以下操作：

if (my_df$class== "foo") {
  my_df$columnB <- my_df$columnA * 2
}else{
  if (my_df$class == "bar") {
    my_df$columnB <- my_df$columnA * 5
  }else{
    my_df$columnB <- my_df$columnA * 10
  }
}

编辑：我也尝试过：

ifelse (my_df$class== "foo",
  my_df$columnB <- my_df$columnA * 2  
  ifelse (my_df$class== "bar",
    my_df$columnB <- my_df$columnA * 5,
    my_df$columnB <- my_df$columnA * 10
  )
)

不用工作，让我以伪代码的形式说明：

As it doesn't work, let me state it in pseudo-code :

for each row, 
    if the value in column class is "foo"
         set the value in column B to be 2 times the value in column A
    if the value in column class is "bar"
         set the value in column B to be 5 times the value in column A
    if the value in column class is something else
         set the value in column B to be 10 times the value in column A

我的问题当然是分配运算符：如果我使用 < - $ / code>整个 columnB 列最后是 columnA 乘以 5 （因为这样发生 class 最后一行的值为 bar ）。

My problem is, of course, with the assigning operator : if I use <- the whole columnB column ends up being columnA multiplied by 5 (because it so happens that the class value of the last row is bar).

任何解决方案？

我将采取一种解决方案来解决我的问题，而不必经过 if / elseif / else 语法，但是如果有人可以提供解决方案来保护这种语法，我也会非常感激，为了学习。

I'll take a solution that solves my problem without going through this if/elseif/else syntax, but I'd also really appreciate it if someone could provide a solution keeping this syntax, for the sake of learning.

谢谢

推荐答案

如果不是矢量化的，所以你可以尝试使用 ifelse

if isnt vectorised so you can try to use ifelse

/ p>

for example

my_df$columnB=ifelse(my_df$class== "foo",my_df$columnA * 2, 
                 ifelse(my_df$class == "bar",my_df$columnA * 5,my_df$columnA * 10))

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