Using model.matrix() to create dummy variables

Question

the following code doesn't work, could someone offer help?

dataframe1<-data.frame(x1 = c(1:5) , x2 = 1 , x3 = 0)
dataframe1
model.matrix(~x1 - 1 , dataframe1)

score 2 · Accepted Answer · answered Jul 07 '21 at 21:33

2

We could also convert to character

dataframe1$x1 <-  as.character(dataframe1$x1)
> model.matrix(~x1 - 1, dataframe1)
  x11 x12 x13 x14 x15
1   1   0   0   0   0
2   0   1   0   0   0
3   0   0   1   0   0
4   0   0   0   1   0
5   0   0   0   0   1

answered Jul 07 '21 at 21:33

akrun

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score 1 · Answer 2 · answered Jul 07 '21 at 03:47

1

Make x1 as factor variable.

dataframe1<-data.frame(x1 = c(1:5) , x2 = 1 , x3 = 0)
dataframe1$x1 <- factor(dataframe1$x1)
model.matrix(~x1 - 1, dataframe1)

#  x11 x12 x13 x14 x15
#1   1   0   0   0   0
#2   0   1   0   0   0
#3   0   0   1   0   0
#4   0   0   0   1   0
#5   0   0   0   0   1
#attr(,"assign")
#[1] 1 1 1 1 1
#attr(,"contrasts")
#attr(,"contrasts")$x1
#[1] "contr.treatment"

answered Jul 07 '21 at 03:47

Ronak Shah

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can i kindly know what does `~x1 -1` mean – Mathilda Fang Jul 07 '21 at 03:48
1

It is used to drop the intercept value from `model.matrix(~x1, dataframe1)` – Ronak Shah Jul 07 '21 at 03:53

Using model.matrix() to create dummy variables

2 Answers2