How to display zero frequency for bars in base R barplot?

When we create a barplot in base R, the bars are plotted for all the values in the vector but if we have a gap in the values then the bar with zero frequency for that gap is not plotted. For example, if we have a vector called x that contains 100 values consisting of 0, 1, 3 then the barplot will not represent zero frequency for 2. To solve this problem, we can use factor function in the barplot function as shown in the below examples.

Example1

Live Demo

> x<-rpois(200,2)
> x

Output

  [1] 0 1 1 1 3 1 3 1 0 1 1 5 1 8 3 2 3 3 3 3 2 4 2 0 5 3 1 0 1 1 4 1 4 2 3 1 3
 [38] 1 4 2 2 5 1 2 5 2 3 1 1 0 1 1 2 3 4 3 1 1 2 1 2 5 1 1 3 3 1 3 1 3 0 4 1 1
 [75] 2 2 5 2 2 1 2 2 3 1 4 2 1 3 2 0 2 1 0 4 1 5 2 3 2 0 1 1 1 1 2 3 1 3 1 3 2
[112] 3 2 4 4 1 1 0 2 6 1 4 0 5 0 1 2 2 2 3 5 2 2 2 1 4 2 2 1 0 0 1 4 4 1 3 5 1
[149] 1 5 1 2 0 1 2 2 1 1 2 1 0 5 2 3 2 3 1 4 1 2 2 1 1 1 0 0 2 0 1 2 3 4 4 4 2
[186] 2 2 1 1 1 1 4 3 2 2 2 1 0 5 2

Example

> barplot(table(factor(x,levels=0:10)))

Output

Example2

> y<-sample(c(1,2,5),100,replace=TRUE)
> barplot(table(factor(y,levels=1:5)))

Output