Add describe() for LazyFrame

[niccolopetti]

Description

Currently describe is not implemented for lazyframes, and you have to first materialize into a Dataframe before being able to call describe , however all methods called into describe seem to be supported by Lazyframe:
polars.LazyFrame.count
polars.LazyFrame.max
polars.LazyFrame.mean
polars.LazyFrame.median
polars.LazyFrame.min
polars.LazyFrame.null_count
polars.LazyFrame.quantile
polars.LazyFrame.std
polars.LazyFrame.sum
polars.LazyFrame.var

so why don't we allow LazyFrame.describe() ?

[stinodego]

describe is meant as a way to get some quick insights in your data. It could work on a LazyFrame, but then you would have to call collect() right after anyway, otherwise you're not much wiser. It just doesn't make sense as a lazy method.

Just collect first and then use describe.

[niccolopetti]

describe is meant as a way to get some quick insights in your data. It could work on a LazyFrame, but then you would have to call collect() right after anyway, otherwise you're not much wiser. It just doesn't make sense as a lazy method.

Just collect first and then use describe.

But what if the Dataframe is so big that it wouldn't fit in memory?

[stinodego]

Fair enough - that seems like a valid use case. I'll re-open to see what others have to say.

[alexander-beedie]

Yup, I think it's worthwhile - I can see that there are plenty of cases where you don't want to materialise GBs of data into a local frame just to run describe() on it 🤔

[mcrumiller]

"looks pretty lazy!" sounds like an accurate description to me, can we just return that?