Implement missing `Expr` methods

[MarcoGorelli]

In https://github.com/narwhals-dev/narwhals-daft/blob/main/narwhals_daft/expr.py there's a list of what's not_implemented for Daft

Any help moving forwards with these would be greatly appreciated 🙏

Task is:

1. Follow the setup instructions on the README
2. Implement some method
3. You can run the tests for that method with run_test.py. E.g.: python run_tests.py -k is_unique to run the is_unique tests
4. Run python update_run_tests.py when you're done, and hopefully the list in run_tests.py will shorten itself!

Feel free to ask for help if anything trips you up

[raisadz]

I will be looking at implementing functions in the string namespace in the next few days

[MarcoGorelli]

thanks! i'd suggesting with just adding a single one (say, len_chars?) and marking all the others as not_implemented for now

[ym-pett]

had a look at remaining functions & I'm going to attempt to implement mode tomorrow. 🤞

update: closed this PR for the time being as I couldn't quite figure out how not to use something which triggers a computation; come to think of it, this would be a good topic for the study group :)

In the meantime, I've added a request for additional descriptive statistics with daft in their existing discussion on having more aggregations: Eventual-Inc/Daft#485

[raisadz]

@ym-pett I will be happy if you want to take some of the string methods, just check this PR first #64. Also, I will try to work on slice tomorrow

[ym-pett]

thanks @raisadz, I'd like to try .to_titlecase().

Oh no it's one of those that don't exist in daft, I will try, can't guarantee 😅