How to create a dummy variable in R?

A dummy variable is a type of variable that takes a value of 1 if the value for which the dummy variable is created exists in the data frame, otherwise it takes 0. Therefore, if we have a one binary variable in a data frame then there will be two dummy variables for the same. To create a dummy variable, we can use model.matrix function as shown in the below examples.

Consider the below data frame −

Example

 Live Demo

Temp<-sample(c("Hot","Cold"),20,replace=TRUE) df1<-data.frame(Temp) df1

Output

   Temp 1  Cold 2  Hot 3  Cold 4  Cold 5  Hot 6  Hot 7  Hot 8  Cold 9  Hot 10 Hot 11 Cold 12 Hot 13 Cold 14 Cold 15 Hot 16 Hot 17 Hot 18 Hot 19 Cold 20 Hot

Creating dummy variable for Temp in df1 −

Example

model.matrix(~Temp-1,data=df1)

Output

  TempCold TempHot 1  1         0 2  0         1 3  1         0 4  1         0 5  0         1 6  0         1 7  0         1 8  1         0 9  0         1 10 0         1 11 1         0 12 0         1 13 1         0 14 1         0 15 0         1 16 0         1 17 0         1 18 0         1 19 1         0 20 0         1

attr(,"assign")

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

Example

 Live Demo

Group<-sample(c("A","B","C"),20,replace=TRUE) df2<-data.frame(Group) df2

Output

   Group 1  B 2  C 3  B 4  A 5  A 6  C 7  C 8  C 9  C 10 A 11 B 12 A 13 A 14 C 15 B 16 B 17 C 18 A 19 C 20 A

Creating dummy variable for Group in df2 −

Example

model.matrix(~Group-1,data=df2)

Output

  GroupA GroupB GroupC 1   0     1      0 2   0     0      1 3   0     1      0 4   1     0      0 5   1     0      0 6   0     0      1 7   0     0      1 8   0     0      1 9   0     0      1 10  1     0      0 11  0     1      0 12  1     0      0 13  1     0      0 14  0     0      1 15  0     1      0 16  0     1      0 17  0     0      1 18  1     0     0 19  0     0     1 20  1     0     0

attr(,"assign")

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