如何将多类变量转换为 R 中的多列？

Question

我有一个如下所示的数据，我想将此变量转换为列，该列应等于变量中的类数。

数据：

  variable
1 red
2 red
3 black
4 red
5 black
6 green
7 black
8 red
9 green

预期输出：

  variable  red   black  green
1 red        1     0     0
2 red        1     0     0
3 black      0     1     0
4 red        1     0     0
5 black      0     1     0
6 green      0     0     1
7 black      0     1     0
8 red        1     0     0
9 green      0     0     1

试过了：

data$red = ifelse(data$variable == "red",1,0)
data$black = ifelse(data$variable == "black",1,0)
data$green = ifelse(data$variable == "green",1,0)

通过使用上面的代码，我实现了我想要的。但是如果我在一个变量中有超过 10 个类，我不想写 10 次代码。那么，有没有最好的方法一次性做到这一点。

Answer 1

df <- read.table(file = "clipboard", sep = "\t", header=T)

df <-data.frame(variable= c("red","red","black","red","black","green",
        "black","red","green"))
df

  variable
1      red
2      red
3    black
4      red
5    black
6    green
7    black
8      red
9    green
class(df$variable)
[1] "factor"
model.matrix(~ . + 0, data=df, contrasts.arg = lapply(df, contrasts, contrasts=FALSE))

  variableblack variablegreen variablered
1             0             0           1
2             0             0           1
3             1             0           0
4             0             0           1
5             1             0           0
6             0             1           0
7             1             0           0
8             0             0           1
9             0             1           0