iterator – Page 30 – Tarik Billa

What does “three dots” in Python mean when indexing what looks like a number?

November 18, 2022 by Tarik

While the proposed duplicate What does the Python Ellipsis object do? answers the question in a general python context, its use in an nditer loop requires, I think, added information. https://docs.scipy.org/doc/numpy/reference/arrays.nditer.html#modifying-array-values Regular assignment in Python simply changes a reference in the local or global variable dictionary instead of modifying an existing variable in place. This … Read more

Cleanest way to get last item from Python iterator

November 18, 2022 by Tarik

If you are using Python 3.x: *_, last = iterator # for a better understanding check PEP 448 print(last) if you are using python 2.7: last = next(iterator) for last in iterator: continue print last Side Note: Usually, the solution presented above is what you need for regular cases, but if you are dealing with … Read more

Iterate over object keys in node.js

November 18, 2022 by Tarik

What you want is lazy iteration over an object or array. This is not possible in ES5 (thus not possible in node.js). We will get this eventually. The only solution is finding a node module that extends V8 to implement iterators (and probably generators). I couldn’t find any implementation. You can look at the spidermonkey … Read more

How do I iterate over a range with a custom step?

November 13, 2022 by Tarik

range_step_inclusive and range_step are long gone. As of Rust 1.28, Iterator::step_by is stable: fn main() { for x in (1..10).step_by(2) { println!(“{}”, x); } }

Update row values where certain condition is met in pandas

November 12, 2022 by Tarik

I think you can use loc if you need update two columns to same value: df1.loc[df1[‘stream’] == 2, [‘feat’,’another_feat’]] = ‘aaaa’ print df1 stream feat another_feat a 1 some_value some_value b 2 aaaa aaaa c 2 aaaa aaaa d 3 some_value some_value If you need update separate, one option is use: df1.loc[df1[‘stream’] == 2, ‘feat’] … Read more

What is the difference between const_iterator and non-const iterator in the C++ STL?

October 25, 2022 by Tarik

const_iterators don’t allow you to change the values that they point to, regular iterators do. As with all things in C++, always prefer const, unless there’s a good reason to use regular iterators (i.e. you want to use the fact that they’re not const to change the pointed-to value).

Ruby: How to iterate over a range, but in set increments?

October 24, 2022 by Tarik

See http://ruby-doc.org/core/classes/Range.html#M000695 for the full API. Basically you use the step() method. For example: (10..100).step(10) do |n| # n = 10 # n = 20 # n = 30 # … end

What does iterator->second mean?

October 22, 2022 by Tarik

I’m sure you know that a std::vector<X> stores a whole bunch of X objects, right? But if you have a std::map<X, Y>, what it actually stores is a whole bunch of std::pair<const X, Y>s. That’s exactly what a map is – it pairs together the keys and the associated values. When you iterate over a … Read more

Deleting elements from std::set while iterating

October 22, 2022 by Tarik

This is implementation dependent: Standard 23.1.2.8: The insert members shall not affect the validity of iterators and references to the container, and the erase members shall invalidate only iterators and references to the erased elements. Maybe you could try this — this is standard conforming: for (auto it = numbers.begin(); it != numbers.end(); ) { … Read more