fix: raise clear error when window_size is too large

[suhr25]

SUMMARY

Fixes a crash when window_size is too large in Fst GWSS by raising a clear error instead of returning empty data.

---

FIX

Before

x = allel.moving_statistic(pos, statistic=np.mean, size=window_size)
return dict(x=x, fst=fst)

After

x = allel.moving_statistic(pos, statistic=np.mean, size=window_size)

if len(x) == 0:
    raise ValueError("window_size is larger than available SNPs")

return dict(x=x, fst=fst)

---

VERIFICATION

Using a large window_size on a small region used to crash with an IndexError. Now it raises a clear ValueError. A test confirms this behavior.

[suhr25]

Hi @jonbrenas,
Kindly take a look at this PR.
Thanks!

[jonbrenas]

Hi @suhr25, would there be a way to instead raise a warning and modify the window_size so that a result is returned?

[suhr25]

Thanks for the suggestion! @jonbrenas
I have updated the behavior to issue a warning and automatically adjust window_size to the available SNP count so the computation can proceed. Also updated tests and documentation accordingly.

Let me know if you would prefer any different handling.

[suhr25]

Hi @jonbrenas,
Kindly take a look,Thanks!

[jonbrenas]

Thanks @suhr25,

Because we want to have a moving statistics, the window size would need to be a factor smaller than the number of SNPs (let's say, 10 by default but it should be a parameter). The window size should thus be adjusted, unless it falls under a given number (again it should be a parameter with a default value say 1 000), in which your original error message probably becomes the solution.

[suhr25]

Sure thanks,
I will look into it.