Will there be any replacement for Arb distinct and distinctB

Question

Will there be any replacement for Arb distinct and distinctBy

sam · Answer

We will add a version that requires a limit of number of iterations to try and then will either error or just return duplicates

sam · Answer

the current version is liable to hang

dave08 · Answer

+1 skin tone 3

sam · Answer

something like arb distinctBy 1000

sam · Answer

mitch · Answer

< dave08> you may be able to emulate distinct sampling using flatMap i e ```Arb list arbInput the input arb 50 100 take 50 100 randomly flatMap randomSample gt Arb of randomSample distinctBy ```

mitch · Answer

Proper distinct needs a bit of thinking

dave08 · Answer

Yeah I guess that s possible but you wouldn t necessarily get the 50 100

dave08 · Answer

Actually I m not even sure you d get them with the current implementation

dave08 · Answer

But yeah distinct isn t easy

mitch · Answer

Arb is a population of data of some type so you re right maybe 50 samples isn t enough to find the needle in the haystack population maybe we need 500 maybe 1000

mitch · Answer

So yeah It s a can of worms we need to see what we can come up with

mitch · Answer

Another difficulty is because distinct is a terminal operation In sequence for instance in order for kotlin to compute distinct it will have to exhaust the whole sequence What s problematic is that well an Arb is a population so the expectation is that whenever we ask for a sample from the population the contract says it will have one ready For instance if we were having a population of ints 1 to 10 and then we call distinct on that arb what would be the expectation Would it a produce 10 distinct elements and then stop Null throw this arb is no longer a population and can t be resampled or b makes sure we sample 1 to 10 in a uniform distribution i e each number 10 of the time This is akin to having a population of 10 numbers that is equally distributed This behaviour effectively is going to weed out imbalances in the initial population e g if the generator of the numbers have a lot of 1s but not many of the other numbers

mitch · Answer

exploding head

dave08 · Answer

Agreed In my case I need to fake a Repository s contents so I m mostly concerned with the table s primary key but I do have other fields that need to be unique Int s can always keep sets of ranges that are left to look in modifying the producing arb but not all other types could do that

dave08 · Answer

Maybe an additional `distinct` param on `<http Arb int|Arb int> ` might be useful though if that s a solution

sam · Answer

I made a proposal that we just push the decisions down to the user tell us what you want to do if we can t generate n distinct values make none distinct or throw

dave08 · Answer

Yeah but in my case with unique db primary keys it depends on how often it will throw just having tests fail because of test framework limits might be frustrating if it happens too often

dave08 · Answer

But then sometimes it s not to common to have collisions in certain data sets so that might be a reasonable proposition in those cases

sam · Answer

Then you would up the limit set the max attempts to 100000000 or whatever you want

sam · Answer

if you re confident it can be filled