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POHow can I implement a data structure that preserves order and has fast insertion/removal?
 

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  1. POHow can I implement a data structure that preserves order and has fast insertion/removal?
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    <p>I'm looking for a data structure that preserves the order of its elements (which may change over the life of the data structure, as the client may move elements around).</p> <p>It should allow fast search, insertion before/after a given element, removal of a given element, lookup of the first and last elements, and bidirectional iteration starting at a given element.</p> <p>What would be a good implementation? </p> <p>Here's my first attempt:</p> <p>A class deriving from both <code>collections.abc.Iterable</code> and <code>collections.abc.MutableSet</code> that contains a linked list and a dictionary. The dictionary's keys are elements, values are nodes in the linked list. The dictionary would handle search for a node given an element. Once an element is found, the linked list would handle insertion before/after, deletion, and iteration. The dictionary would be updated by adding or deleting the relevant key/value pair. Clearly, with this approach the elements must be hashable and unique (or else, we'll need another layer of indirection where each element is represented by an auto-assigned numeric identifier, and only those identifiers are stored as keys).</p> <p>It <em>seems to me</em> that this would be strictly better in asymptotic complexity than either <code>list</code> or <code>collections.deque</code>, but I may be wrong. [EDIT: Wrong, as pointed out by @roliu. Unlike <code>list</code> or <code>deque</code>, I would not be able to find an element by its numeric index in <code>O(1)</code>. As of now, it is <code>O(N)</code> but I am sure there's some way to make it <code>O(log N)</code> if necessary.]</p>
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    1. CO`collections.OrderedDictionary` is a dict using doubly-linked lists to maintain order. However, rearranging the order arbitrarily is not trivial.
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      1. POHow can I implement a data structure that preserves order and has fast insertion/removal?
      1. USMartijn Pieters
    2. COHow would do fast insertion with your dictionary + linked list? Any abstract data structure built on a balanced binary search tree seems like it'd work for you (it's reasonably fast for insertion, removal, search and can be iterated forwards and backwards from any node). Not sure what there is in python though.
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      1. POHow can I implement a data structure that preserves order and has fast insertion/removal?
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    3. COAs it stands this question has some faults: it is too broad (multiple questions in one post), asks for external resources (explicitly off-topic) and is not a practical code problem (better suited to Programmers.SE).
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      1. POHow can I implement a data structure that preserves order and has fast insertion/removal?
      1. USMartijn Pieters
 

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