r - table frequencies with custom column -

for example, have matrix:

a <- c(2,3,4,3,3,2,2) table(a) 

output:

2 3 4  3 3 1  

but output want is:

1 2 3 4  0 3 3 1  

so example, value range 1 4.... because of random value, list may doesnt contain 1 or more element range when value range 1 4, want table have 4 coloumns not exist value filled 0 (0)

you can convert 'a' 'factor' , specify levels before doing table

table(factor(a, levels=seq_len(max(a)))) #1 2 3 4  #0 3 3 1  

if need custom level should specified well. using example comments,

a<- c(2,3,3,3,2,2) table(factor(a, levels=1:4)) #1 2 3 4  #0 3 3 0