Question

Is there an elegant method to create a number that does not exist in a given list of floating point numbers? It would be nice if this number were not close to the existing values in the array.

For example, in the list [-1.5, 1e+38, -1e38, 1e-12] it might be nice to pick a number like 20 that’s “far” away from the existing numbers as opposed to 0.0 which is not in the list, but very close to 1e-12.

The only algorithm I’ve been able to come up with involves creating a random number and testing to see if it is not in the array. If so, regenerate. Is there a better deterministic approach?

Answer 1

If you have the constraint, that the new value must be somewhere in between [min, max] then you could sort your values and insert the mean value of the two adjacent values with the largest absolute difference.

In your sample case [-1e38, -1.5, 1e-12, 1e+38] is the ordered list. As you calculate the absolute differences, you’ll find the maximum difference for the values (1e-12, 1e+38) so you calculate the new value to be ((n[i+1] - n[i]) / 2) + n[i] (simple mean value calculation).

Update:
Additionally you could also check if the FLOAT_MAX or FLOAT_MIN values will give good candidates. Simply check their distance to min and max and if the result values are larger than the maximum difference for two adjacent values, pick them.