Count missing variables in dataset

I have a problem about how to count missing variables in dataset.
I have a question for my customer. They are must choice one of answer
for example: A, B, C, D and E.
Now, I have dataset which is the result from my question, for
instance:

x1 x2 x3 x4 x5
A  A  A   B  A
C  A  A   A  A
B  B  A   B  A
B  B  B   C  A
A  B  B   B  B
C  B  B   B  A

I know that my customer only choice A, B and C.
Are there any way to count variables that are not include in dataset.
I mean D and E is missing in dataset.
You just need to set up the variables properly. If you just say:

R> x <- factor(sample(LETTERS[1:3], 5, replace = TRUE))
R> summary(x)
A B C 
1 2 2 

R will assume that the only levels available are A-C. But if you tell R

R> x <- factor(x, levels = LETTERS[1:5])
R> summary(x)
A B C D E 
1 2 2 0 0 

it will do what you want. Just provide the full choice set as levels to
the corresponding variables.
Z
Thanks for your help.
Jan Sabee

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Count missing variables in dataset

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