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Questions tagged [iterator]

An iterator is an object-oriented programming pattern that allows traversal through a collection, agnostic of the actual implementation or object addresses in physical memory. It is one of the Gang of Four's behavioral design patterns.

An iterator is an object-oriented programming pattern which, for the most part, functions similarly to a pointer to an object inside a collection with the added ability to traverse through the collection in a defined manner, agnostic of the actual implementation or even object addresses in physical memory.

The following types of iterators are the most common:

  • Forward
  • Reverse
  • Bidirectional
  • Random Access

Iterators may be read-only, write-only or read-write.

  • Forward iterators typically have a next method
  • Reverse iterators typically have a previous method
  • Iterators sometimes have a remove method

This is one of the Gang of Four's behavioral , first published in Gamma et al.'s book "Design Patterns: Elements of Reusable Object-Oriented Software".

The Gang of Four pattern is discussed separately on Wikipedia.

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What does the "yield" keyword do in Python?

What is the use of the yield keyword in Python? What does it do? For example, I'm trying to understand this code1: def _get_child_candidates(self, distance, min_dist, max_dist): if self._leftchild and distance - max_dist < self._median: …
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How do I iterate through two lists in parallel?

I have two iterables, and I want to go over them in pairs: foo = [1, 2, 3] bar = [4, 5, 6] for (f, b) in iterate_together(foo, bar): print("f:", f, " | b:", b) That should result in: f: 1 | b: 4 f: 2 | b: 5 f: 3 | b: 6 One way to do it…
Nathan Fellman
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How can I iterate over files in a given directory?

I need to iterate through all .asm files inside a given directory and do some actions on them. How can this be done in a efficient way?
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Difference between Python's Generators and Iterators

What is the difference between iterators and generators? Some examples for when you would use each case would be helpful.
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How to build a basic iterator?

How can I create an iterator in Python? For example, suppose I have a class whose instances logically "contain" some values: class Example: def __init__(self, values): self.values = values I want to be able to write code like: e =…
akdom
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How to iterate (keys, values) in JavaScript?

I have a dictionary that has the format of dictionary = {0: {object}, 1:{object}, 2:{object}} How can I iterate through this dictionary by doing something like for ((key, value) in dictionary) { //Do stuff where key would be 0 and value would…
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Calling remove in foreach loop in Java

In Java, is it legal to call remove on a collection when iterating through the collection using a foreach loop? For instance: List names = .... for (String name : names) { // Do something names.remove(name). } As an addendum, is it…
Michael Bobick
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How to convert an Iterator to a Stream?

I am looking for a concise way to convert an Iterator to a Stream or more specifically to "view" the iterator as a stream. For performance reason, I would like to avoid a copy of the iterator in a new list: Iterator sourceIterator =…
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Iterator invalidation rules for C++ containers

What are the iterator invalidation rules for C++ containers? (Note: This Q&A is an entry in Stack Overflow's C++ FAQ. Meta-discussion about the question itself should be posted on the Meta question that started all of this, not here.)
Lightness Races in Orbit
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What are iterator, iterable, and iteration?

What are "iterable", "iterator", and "iteration" in Python? How are they defined? See also: How to build a basic iterator?
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Get the first item from an iterable that matches a condition

I would like to get the first item from a list matching a condition. It's important that the resulting method not process the entire list, which could be quite large. For example, the following function is adequate: def first(the_iterable, condition…
Chris Phillips
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How do I get the index of an iterator of an std::vector?

I'm iterating over a vector and need the index the iterator is currently pointing at. What are the pros and cons of the following methods? it - vec.begin() std::distance(vec.begin(), it)
cairol
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C++ Loop through Map

I want to iterate through each element in the map without knowing any of its string-int values or keys. What I have so far: void output(map table) { map::iterator it; for (it = table.begin(); it…
NoName
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How to avoid "ConcurrentModificationException" while removing elements from `ArrayList` while iterating it?

I'm trying to remove some elements from an ArrayList while iterating it like this: for (String str : myArrayList) { if (someCondition) { myArrayList.remove(str); } } Of course, I get a ConcurrentModificationException when trying to…
Ernestas Gruodis
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Sorting a vector in descending order

Should I use std::sort(numbers.begin(), numbers.end(), std::greater()); or std::sort(numbers.rbegin(), numbers.rend()); // note: reverse iterators to sort a vector in descending order? Are there any benefits or drawbacks with one approach…
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