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Comment by candiodari | Hacker News Reader

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candiodari·

> Chunked and windowed iteration, in iterutils

I need this. Makes so many functional expressions so simple.

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See also more-itertools for lots of other things in this vein.

Could you give some examples?

I wrote some similar code one time that generated SQL which was manually reviewed. It generated a massive WHERE IN clause. Oracle only accepts 1000 values. So I fed it a list of thousands of values, and it chunked them into rows of N objects, and into larger chunks of 1000. Having some code to do that automatically would be quite nice.

Why not insert the values in WHERE IN to a temporary helper table and join on that? It seems somewhat easier and might perform better.

Oracle has a limit on the number of parameters in a query, not just in the `WHERE IN` clause. So you'd need to insert them into the helper table in batches of 1000.

Good point, but isn’t that done automatically by whatever tool your using?

And if the table your selecting from is big enough I would expect that this setup would be faster but it’s hard to say. It would also more easily guarantee that your results will be consistent.

Two that I run into all the time: 1. pairwise iteration over a (cylic) list of points representing the ordered vertices of a polygon will give you a sequence of edges

2. np.diff, takes differences between consecutive pairs. Sometimes you have a different kind of "difference" operation, though. The pairwise iteration helps you express that.

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