我需要将分类变量转换为多个二分(“虚拟”)变量以用于逻辑回归。说我的数据框是:
tdf <- data.frame(first=sample(c("A", "B", "C", "D"), 100, replace=T),
lobe = sample(c("RUL", "RML", "RLL", "LUL", "LLL"), 100, replace=T),
continuous=sample(1:100, 100),
smoker = sample(c("never", "less20", "more20"), 100, replace=T)
)
我可以手动执行
first. <- with (tdf, factor (first))
dummies <- model.matrix(~ first.)
dummies <- dummies[,-1]
tdf <- cbind(tdf, dummies)
请注意,将因子称为“第一”非常重要。 (或更一般地说,“变量”。)因为虚拟变量会将此前缀继承到它们各自的名称中,以便以后更容易识别它们('variable1.factor2','variable1.factor3'等)。
我的问题是:如何使用以编程方式分配变量名称的函数来执行此操作:
dummify <- function(df, vectorOfColIndices) {
cn <- colnames(df)
for (i in vectorOfColIndices) {
t. <- with (tdf, factor (df[i])) # temporary factor
assign (cn[i], t.) # give it the proper 'Variable.' name
dummies <- model.matrix(~ ????) # Stuck here: how do I call this newly created structure?
...
}
}
这样我以后可以像这样转换数据帧:
vd <- c(1,2,4) # columns that need to be converted into dummy vars
df <- dummify(df, vd)
答案 0 :(得分:2)
dummify <- function( df , col.indicies.to.add.dummies ) {
for ( i in names( df )[ col.indicies.to.add.dummies ] ) {
t. <- with( df , factor( df[ , i] ) )
dummies <- model.matrix( ~t. )
colnames( dummies ) <- paste( i , levels( t. ) , sep = "." )
dummies <- dummies[ , -1 ]
df <- cbind( df , dummies )
}
df
}
答案 1 :(得分:2)
同意Dason的评论,即你不应该有很多情况需要手动创建假人。而且,如果你做安东尼的解决方案就好了。我提出这个替代方案只是为了好玩:)
dummify <- function(df, vectorOfColIndices) {
for (i in vectorOfColIndices) {
var <- paste(names(df)[i], ".", sep="")
assign(var, df[[i]])
df <- cbind(df, model.matrix(reformulate(var))[, -1])
}
return(df)
}