6.R

# a few useful functions...
is.even <- function(x) sum(x %% 2 == 0) == length(x)
is.odd <- function(x) sum(x %% 2 != 0) == length(x)

# and finally, the calculation
can_be_inferred <- sum(apply(lrpp_streets_for_inference, 1, function (row) {
    aons <- lrpp_addresses_with_numeric_aon[(lrpp_addresses_with_numeric_aon$street == row[1]) & (lrpp_addresses_with_numeric_aon$pcd == row[2]), "aon"]
    # if all numbers I know are odd or even, I can only infer the missing odd and even numbers,
    # otherwise I can infer all
    # TODO: crazy below: why row[3] and row[4] are not numeric any longer?
    inferred <- setdiff(seq(from = as.numeric(row[3]), to = as.numeric(row[4]), by = ifelse(is.even(aons) | is.odd(aons), 2, 1)), aons)        
    return(length(inferred))    
}))

output

> can_be_inferred
[1] 190285
>