Unicity of values in R

Question

I need some help with R. I'm not an expert and just began using it.

I need to check the unicity of values in a table and would like to know how I can do that.

Let say I have a contractID and a contractNumber in the data frame Contract2008 I would like to make sure that there is only 1 contractNumber by Contract ID. I did this :

DT <- data.table(contract2008)
DT[, .(number_of_distinct_numcontract = length(unique("contractNumeber"))), by = "ContractID"]

Is this the right way to do it?

Thank you for your help