Question

我在数据框中有100个分类变量，我想为我的预测模型创建交互。我创建了一个循环来完成它，但我最终得到重复。

df <- data.frame(Col1=c("A","B","C"), 
                 Col2=c("F","G","H"), 
                 Col3=c("X","Y","Z"))

这给了我们：

  Col1 Col2 Col3
1    A    F    X
2    B    G    Y
3    C    H    Z

当我运行代码以使用

创建交互变量时

vars <- colnames(df) 
for (i in vars)  {
  for (j in vars) {
    if (i != j) {
      df[,c(paste0(i, j))] <- paste(df[[i]],df[[j]],sep='*')}}}

我最终得到的副本如Col1Col2与Col2Col1相同。

> str(df)
'data.frame':   3 obs. of  9 variables:
 $ Col1    : Factor w/ 3 levels "A","B","C": 1 2 3
 $ Col2    : Factor w/ 3 levels "F","G","H": 1 2 3
 $ Col3    : Factor w/ 3 levels "X","Y","Z": 1 2 3
 $ Col1Col2: chr  "A*F" "B*G" "C*H"
 $ Col1Col3: chr  "A*X" "B*Y" "C*Z"
 $ Col2Col1: chr  "F*A" "G*B" "H*C"
 $ Col2Col3: chr  "F*X" "G*Y" "H*Z"
 $ Col3Col1: chr  "X*A" "Y*B" "Z*C"
 $ Col3Col2: chr  "X*F" "Y*G" "Z*H"

有没有办法删除这些重复项？

Answer 1

您无需为每对变量创建显式交互列。相反，模型公式中的Col1 * Col2会自动生成交互。例如，如果您的结果变量是y（这将是数据框中的列），并且您希望回归公式包含其他列之间的所有双向交互，则可以执行以下操作：

form = reformulate(apply(combn(names(df)[-grep("y", names(df))], 2), 2, paste, collapse="*"), "y")

form

y ~ Col1 * Col2 + Col1 * Col3 + Col2 * Col3

那么你的回归模型将是：

mod = lm(form, data=df)

Answer 2

您问题的可能答案： How to automatically include all 2-way interactions in a glm model in R

You can do two-way interactions simply using `.*.` and arbitrary n-way interactions writing `.^n`. `formula(g)` will tell you the expanded version of the formula in each of these cases.

Answer 3

一个选项可能是使用combn和apply函数。一个自定义函数需要打印由*分隔的两个分类值（例如A*F）。

# data
df <- data.frame(Col1=c("A","B","C"), 
                 Col2=c("F","G","H"), 
                 Col3=c("X","Y","Z"))

#function to paste two values together in A*F format
multiplyit <- function(x){
  paste(x, collapse = "*")
}

# Call combn using apply
df2 <- t(apply(df, 1, combn, 2, multiplyit))

#generate and set column names of df2
colnames(df2) <- paste("Col", combn(1:3, 2, paste, collapse="Col"), sep="")

#combine df and df2 to get the final df
df_final <- cbind(df, df2)

df_final
#  Col1 Col2 Col3 Col1Col2 Col1Col3 Col2Col3
#1    A    F    X      A*F      A*X      F*X
#2    B    G    Y      B*G      B*Y      G*Y
#3    C    H    Z      C*H      C*Z      H*Z

循环遍历数据框中的变量以创建交互

3 个答案: