Convert a factor to indicator variables? [duplicate]

Answer 1

One way is to use model.matrix():

model.matrix(~Species, iris)

    (Intercept) Speciesversicolor Speciesvirginica
1             1                 0                0
2             1                 0                0
3             1                 0                0

....

148           1                 0                1
149           1                 0                1
150           1                 0                1
attr(,"assign")
[1] 0 1 1
attr(,"contrasts")
attr(,"contrasts")$Species
[1] "contr.treatment"

Answer 2

There are several ways to do it, but you can use model.matrix :

color <- factor(c("red","green","red","blue"))
data.frame(model.matrix(~color-1))
#   colorblue colorgreen colorred
# 1         0          0        1
# 2         0          1        0
# 3         0          0        1
# 4         1          0        0

Answer 3

try this:

myfactors<-factor(sample(c("f1","f2","f3"),10,replace=T));
myIndicators<-diag(nlevels(myfactors))[myfactors,];

Answer 4

If I understood your question correctly, use model.matrix command, like this.

dd <- data.frame(a = gl(3,4), b = gl(4,1,12))
model.matrix(~ a + b, dd)
   (Intercept) a2 a3 b2 b3 b4
1            1  0  0  0  0  0
2            1  0  0  1  0  0
3            1  0  0  0  1  0
4            1  0  0  0  0  1
5            1  1  0  0  0  0
6            1  1  0  1  0  0
7            1  1  0  0  1  0
8            1  1  0  0  0  1
9            1  0  1  0  0  0
10           1  0  1  1  0  0
11           1  0  1  0  1  0
12           1  0  1  0  0  1
attr(,"assign")
[1] 0 1 1 2 2 2
attr(,"contrasts")
attr(,"contrasts")$a
[1] "contr.treatment"

attr(,"contrasts")$b
[1] "contr.treatment"