Is it possible to auto-fill with zeroes when subtracting output of two calls to `summary` on factors?

Suppose I want to compare two lists of equal size using the frequency of values in each list. Consider the following script. ``` foo = c(24,24,24,3,10,2) bar = c(24,24,10,3,3,2) summary(as.factor(foo)) summary(as.factor(bar)) summary(as.factor(foo)) - summary(as.factor(bar)) ``` As long as the set of discrete values in `foo` and `bar` are identical, this works reasonably well. Here is some output: ``` 2 3 10 24 1 1 1 3 2 3 10 24 1 2 1 2 2 3 10 24 0 -1 0 1 ``` However, if there is some value in `bar` which is not in `foo`, then, we get the undesirable default behavior of recycling the shorter vector and also a mismatch of counts. Consider the case where ``` bar = c(24,24,11,3,10,2) ``` Then, our output looks like this, along with a warning message. ``` 2 3 10 24 1 1 1 3 2 3 10 11 24 1 1 1 1 2 2 3 10 11 24 0 0 0 2 -1 Warning message: In summary(as.factor(foo)) - summary(as.factor(bar)) : longer object length is not a multiple of shorter object length ``` The desired output is: ``` 2 3 10 11 24 0 0 0 -1 1 ``` In particular, note that a `0` has been filled for the missing `11` in `foo`, and that the value for `24` is `3 - 2 = 1` . How can I achieve the desired output?