How to find the number of levels in R for a factor column?

To find the number of levels in R for a factor column, we can use length function along with unique function. For example, if we have a data frame called df that contains a factor column X then we can find the number of levels in the factor column using the command −

length(unique(df$X))

Example

Consider the below data frame −

 Live Demo

x1<-sample(c("A","B","C"),20,replace=TRUE)
y1<-sample(0:9,20,replace=TRUE)
df1<-data.frame(x1,y1)
df1

Output

   x1 y1
1  C  8
2  B  9
3  B  2
4  A  7
5  A  8
6  C  4
7  B  0
8  C  3
9  B  3
10 A  5
11 A  8
12 B  0
13 A  6
14 C  2
15 A  4
16 B  7
17 A  9
18 B  1
19 B  3
20 A  5

Finding the number of levels in column x1 −

Example

length(unique(df1$x1))

Output

[1] 3

Example

 Live Demo

x2<-sample(c("id1","id2","id3","id4"),20,replace=TRUE)
y2<-rnorm(20,1,0.05)
df2<-data.frame(x2,y2)
df2

Output

    x2    y2
1  id2  1.0582275
2  id4  0.8763659
3  id4  1.0091340
4  id1  1.0087233
5  id1  1.0022543
6  id3  0.9682852
7  id3  0.9458475
8  id2  1.0329383
9  id3  0.9890525
10 id1  0.9814830
11 id4  0.9732973
12 id1  1.0644264
13 id3  0.9328492
14 id1  0.9064330
15 id2  0.9781466
16 id2  0.9633579
17 id1  0.9985626
18 id4  1.0428324
19 id4  1.0047497
20 id4  0.9717654

Finding the number of levels in column x2 −

Example

length(unique(df2$x2))

Output

[1] 4