R中if（）和ifelse（）函数之间的区别 [英] Difference between if() and ifelse() functions in R

问题描述

我想要伪代码，即为列Species创建标志变量。

I want to dummy code i.e. create flag variables for column Species.

我写了下面的代码：

create_dummies<-function(data, categorical_preds){
    if (categorical_preds=="setosa"){data$setosa_flg<-1}
    else {data$setosa_flg<-0}
    if (categorical_preds=="versicolor"){data$versicolor_flg<-1}
    else {data$versicolor_flg<-0}
    if (categorical_preds=="virginica"){data$virginica_flg<-1}
    else {data$virginica_flg<-0}
    return(data)
}
create_dummies(iris,iris$Species)

我收到了警告：

Warning messages:
1: In if (categorical_preds == "setosa") { :
  the condition has length > 1 and only the first element will be used
2: In if (categorical_preds == "versicolor") { :
  the condition has length > 1 and only the first element will be used
3: In if (categorical_preds == "virginica") { :
  the condition has length > 1 and only the first element will be used

然后我将代码更改为：

create_dummies<-function(data, categorical_preds){
    ifelse(categorical_preds=="setosa",data$setosa_flg<-1,data$setosa_flg<-0)
    ifelse(categorical_preds=="versicolor",data$versicolor_flg<-1,data$versicolor_flg<-0)
    ifelse(categorical_preds=="virginica",data$virginica_flg<-1,data$virginica_flg<-0)

    return(data)
}
create_dummies(iris,iris$Species)

这次没有警告但是新的虚拟变量总是为0。

No warning this time but the new dummy variables are always 0.

下一步我想避免硬编码所以我写了

As a next step I want to avoid hardcoding so i wrote

create_dummies<-function(data, categorical_preds){
catvar<-(unique(categorical_preds))

for (i in 1:length(catvar)){
  iris[catvar[i]]<-ifelse(iris$Species==catvar[i],1,0)
}
return(data)
}
create_dummies(iris,iris$Species)

这有什么问题？

问题：

1. 为什么2个版本的代码无效？

1. Why the 2 versions of the code is not working?

if（）{} 和 ifelse（）功能有什么区别在R？

What is difference between if(){} and ifelse() function in R?

在 ifelse（）中，如果条件为为真，如何进行多项操作？

示例： ifelse（categorical_preds ==setosa，数据$ setosa_flg< -1 print（iris $ Species ），data $ setosa_flg< -0）。

In ifelse(), if the condition is true, how can I do multiple action?
example: ifelse(categorical_preds=="setosa",data$setosa_flg<-1 print(iris$Species),data$setosa_flg<-0).

推荐答案

警告信息：

  the condition has length > 1 and only the first element will be used

告诉你在如果条件相当于使用其第一个元素：

tells you that using a vector in if condition is equivalent to use its first element :

[if (v == 1)] ~ [if (v[1] == 1)] ## v here is a vector

您应该使用向量化的 ifelse 。例如，您可以这样写下您的条件：

You should use the vectorized ifelse. For example you can write your condition like this:

create_dummies<-function(data, categorical_preds){
  ## here I show only the first condition 
  data$setosa_flg <-
       ifelse (categorical_preds=="setosa",1,0)
  data
}

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