hashtable

I have recently been working with hash tables in Common Lisp. I have been wondering how to make a separate copy of a hash table containing all the same values as the first. Is there an official way to do this? If not, can you give me an example using maphash? Sim As clhs does not list a copy table function I'd assume that maphash is the way to go. (defun copy-table (table) (let ((new-table (make-hash-table :test (hash-table-test table) :size (hash-table-size table)))) (maphash #'(lambda(key value) (setf (gethash key new-table) value)) table) new-table)) (let ((table (make-hash-table))) (mapcar

Hey, how could I do this as short as possible? Thanks :-) Florian Reischl Try this: System.Collections.Hashtable ht = new System.Collections.Hashtable(); List<string> list = ht.Keys.Cast<string>().ToList(); 来源： https://stackoverflow.com/questions/3297558/create-a-liststring-from-hashtable-keys

The best look-up structure is a HashTable . It provides constant access on average (linear in worst case). This depends on the hash function. Ok. My question is the following. Assuming a good implementation of a HashTable e.g. HashMap is there a best practice concerning the keys passed in the map?I mean it is recommended that the key must be an immutable object but I was wondering if there are other recommendations. Example the size of the key? For example in a good hashmap (in the way described above) if we used String as keys, won't the "bottleneck" be in the string comparison for equals

I have the following class: (defclass category () ((cat-channel-name :accessor cat-channel-name :initarg :cat-channel-name :initform "" :type string :documentation "Name of the channel of this category") (cat-min :accessor cat-min :initarg :min :initform 0 :type number :documentation "Mininum value of category") (cat-max :accessor cat-max :initarg :max :initform 1 :type number :documentation "Maximum value of category")) (:documentation "A category")) Now, I would like to use this class as a key for a hash-table. The addresses of instances can be easily compared with eq . The problem is

I tried looking for an answer to this around the forum/google, but I can't find anything. My issue is this (from python console): >>> import pandas cannot import name hashtable Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python27\lib\site-packages\pandas\__init__.py", line 6, in <module> from . import hashtable, tslib, lib ImportError: cannot import name hashtable //also can't import name NaT somtimes I ran the windows 1-click installer prior to attempting the import. I'm running everything 32-bit. The pandas installer is for python 2.7. Here's a list of

What load factor should I use when I really know the maximum possible no of elements in a HashSet ? I had heard that the default load factor of 0.75 is recommended as it offers good performance trade-offs between speed & space. Is this correct ? However a larger size HashSet would also takes more time in creation and more space. I am using HashSet just inorder to remove duplicate integers from a list of integers. I spent some time playing around with load factors once, and it is shocking how little difference that setting really makes in practice. Even setting it to something high like 2.0

I have been told that Hashtable in .NET uses rehashing in order to reduce/avoid collision. Ie. “Rehasing works as follows: assume we have a set of hash different functions, H1 ... Hn, and when inserting or retrieving an item from the hash table, initially the H1 hash function is used. If this leads to a collision, H2 is tried instead and onwards up to Hn to avoid collision in Hashtable.” Assumption: We have a hashtable with n (where n < Infinity) element where asymptotic time complexity is o(1); we (CLR) have achieved this while applying some hashing function ( Hn-1 hash function where n>1).

Assuming that we have a set of elements and want to store them in a hash map (for example std::unordered_set ), and each element has a key of type uint64_t whose value can vary from 0 to its maximum possible value, is it the best choice to use trivial hash function, where a hash value of a key is the key itself? Does it depend on container in use (i.e. Google's sparse hash vs std::unordered_map from STL)? The probability of appearance of key values is unknown. If all you have to hash is a uint64_t of any possible value with unknown probabilities, and your output must be a uint64_t, then you

Can someone help me shorten the following method? I began with this, which I liked just fine: def self.some_hash { "foo" => "bar" } end Now I want to add an optional key. The tersest syntax I can think of is this: def self.some_hash(some_key=nil) answer = { "foo" => "bar" } answer[some_key] = "yucky, long-winded syntax" if some_key answer end The modified method works, but I'm dissatisfied with waste of virtual ink. Is there a way to shorten it? I realize one could employ a ternary operator on the hash literal, but that would force (I think) the repetition the "foo" => "bar" pair on each