如何在 R 中创建虚拟变量? [英] How do I make a dummy variable in R?

问题描述

因此，我的数据集由 15 个变量组成，其中一个(性别)只有 2 个级别.我想将其用作虚拟变量，但级别为 1 和 2.我该怎么做?我想要 0 级和 1 级，但我不知道如何在 R 中管理它！

So, my data set consists of 15 variables, one of them (sex) has only 2 levels. I want to use it as a dummy variable, but the levels are 1 and 2. How do I do this? I want to have levels 0 and 1, but I don't know how to manage this in R!

推荐答案

使用大多数带有公式界面的 R 建模工具，您无需创建虚拟变量，处理和解释公式的底层代码将执行此操作你.如果您出于其他原因想要一个虚拟变量，那么有几种选择.最简单的(恕我直言)是使用 model.matrix():

With most of R's modelling tools with a formula interface you don't need to create dummy variables, the underlying code that handles and interprets the formula will do this for you. If you want a dummy variable for some other reason then there are several options. The easiest (IMHO) is to use model.matrix():

set.seed(1)
dat <- data.frame(sex = sample(c("male","female"), 10, replace = TRUE))

model.matrix( ~ sex - 1, data = dat)

给出:

> dummy <- model.matrix( ~ sex - 1, data = dat)
> dummy
   sexfemale sexmale
1          0       1
2          0       1
3          1       0
4          1       0
5          0       1
6          1       0
7          1       0
8          1       0
9          1       0
10         0       1
attr(,"assign")
[1] 1 1
attr(,"contrasts")
attr(,"contrasts")$sex
[1] "contr.treatment"

> dummy[,1]
 1  2  3  4  5  6  7  8  9 10 
 0  0  1  1  0  1  1  1  1  0

您可以将dummy 的任一列用作数字虚拟变量；选择您想要作为基于 1 级别的任何列.dummy[,1]选择1代表女班，dummy[,2]代表男班.

You can use either column of dummy as a numeric dummy variable; choose whichever column you want to be the 1-based level. dummy[,1] chooses 1 as representing the female class and dummy[,2] the male class.

如果您希望将其解释为分类对象，请将其作为因子进行转换:

Cast this as a factor if you want it to be interpreted as a categorical object:

> factor(dummy[, 1])
 1  2  3  4  5  6  7  8  9 10 
 0  0  1  1  0  1  1  1  1  0 
Levels: 0 1

但这就是打败了factor的对象；0又是什么?

But that is defeating the object of factor; what is 0 again?

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