To find the number of levels in R for a factor column, we can use the length function with the unique function. For example, if we have a data frame named df with a factor column X, we can use the following command to find the number of levels in the factor column −

length (unique(df$X))

Example

Consider the following dataframe -

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

output result

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

Find the number of levels in column x1 -

Example

length (unique(df1$x1))

output result

[ 1 ]  3

Example

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

output result

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

Find the number of levels in column x2 -

Example

length (unique(df2$x2))

output result

[ 1 ]  4