[R] Best way to store negative indexes

[Peter Dalgaard]

StephaneDemurget <demurget at aleks.com> writes:

> Hi,
> 
> I'm trying to figure out how to properly construct a graph of
> frequencies of a difference between 2 values, that is | i | - | j |.
> I'd like to know the best way to store the actual data because of
> course doing my_vector[i -j] will not work because the index could be
> negative.
> 
> I know there's no hash table so what's the best solution,
> simplicity-wise ? Use a list of pair of values {index, i - j} ? Or can
> I somehow use negative index, perhaps using 0array ? Any help would be
> appreciated :)

(i and j are integer vectors, right?)
How about this:

  f <- i - j
  f <- factor(f,levels=min(f):max(f))
  table(f)

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