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• From string to hex MD5 hash and back

  - by Pablo Fernandez

  I have this pseudo-code in java: bytes[] hash = MD5.hash("example"); String hexString = toHexString(hash); //This returns something like a0394dbe93f bytes[] hexBytes = hexString.getBytes("UTF-8"); Now, hexBytes[] and hash[] are different. I know I'm doing something wrong since hash.length() is 16 and hexBytes.length() is 32. Maybe it has something to do with java using Unicode for chars (just a wild guess here). Anyways, the question would be: how to get the original hash[] array from the hexString. The whole code is here if you want to look at it (it's ~ 40 LOC) http://gist.github.com/434466 The output of that code is: 16 [-24, 32, -69, 74, -70, 90, -41, 76, 90, 111, -15, -84, -95, 102, 65, -10] 32 [101, 56, 50, 48, 98, 98, 52, 97, 98, 97, 53, 97, 100, 55, 52, 99, 53, 97, 54, 102, 102, 49, 97, 99, 97, 49, 54, 54, 52, 49, 102, 54] Thanks a lot!

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• Strange ruby behavior when using Hash.new([])

  - by Valentin Vasilyev

  Consider this code: h=Hash.new(0) #new hash pairs will by default have 0 as values h[1]+=1 # {1=>1} h[2]+=2 # {2=>2} that's all fine, but: h=Hash.new([]) #empty array as default value h[1]<<=1 #{1=>[1]} - OK h[2]<<=2 #{1=>[1,2], 2=>[1,2]} # why ?? At this point I expect the hash to be: {1=>[1], 2=>[2]} But something goes wrong. Does anybody know what happens?

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• How to get the top keys from a hash by value

  - by Kirs Kringle

  I have a hash that I sorted by values greatest to least. How would I go about getting the top 5? There was a post on here that talked about getting only one value. What is the easiest way to get a key with the highest value from a hash in Perl? I understand that so would lets say getting those values add them to an array and delete the element in the hash and then do the process again? Seems like there should be an easier way to do this then that though. My hash is called %words. use strict; use warnings; use Tk; #Learn to install here: http://factscruncher.blogspot.com/2012/01/easy-way-to-install-tk- on-strawberry.html #Reading in the text file my $file0 = Tk::MainWindow->new->Tk::getOpenFile; open( my $filehandle0, '<', $file0 ) || die "Could not open $file0\n"; my @words; while ( my $line = <$filehandle0> ) { chomp $line; my @word = split( /\s+/, lc($line)); push( @words, @word ); } for (@words) { s/[\,|\.|\!|\?|\:|\;|\"]//g; } #Counting words that repeat; put in hash my %words_count; $words_count{$_}++ for @words; #Reading in the stopwords file my $file1 = "stoplist.txt"; open( my $filehandle1, '<', $file1 ) or die "Could not open $file1\n"; my @stopwords; while ( my $line = <$filehandle1> ) { chomp $line; my @linearray = split( " ", $line ); push( @stopwords, @linearray ); } for my $w ( my @stopwords ) { s/\b\Q$w\E\B//ig; } #Comparing the array to Hash and deleteing stopwords my %words = %words_count; for my $stopwords ( @stopwords ) { delete $words{ $stopwords }; } #Sorting Hash Table my @keys = sort { $words{$b} <=> $words{$a} or "\L$a" cmp "\L$b" } keys %words; #Starting Statistical Work my $value_count = 0; my $key_count = 0; #Printing Hash Table $key_count = keys %words; foreach my $key (@keys) { $value_count = $words{$key} + $value_count; printf "%-20s %6d\n", $key, $words{$key}; } my $value_average = $value_count / $key_count; #my @topwords; #foreach my $key (@keys){ #if($words{$key} > $value_average){ # @topwords = keys %words; # } #} print "\n", "The number of values: ", $value_count, "\n"; print "The number of elements: ", $key_count, "\n"; print "The Average: ", $value_average, "\n\n";

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• Python hash() can't handle long integer?

  - by Xie

  I defined a class: class A: ''' hash test class a = A(9, 1196833379, 1, 1773396906) hash(a) -340004569 This is weird, 12544897317L expected. ''' def __init__(self, a, b, c, d): self.a = a self.b = b self.c = c self.d = d def __hash__(self): return self.a * self.b + self.c * self.d Why, in the doctest, hash() function gives a negative integer?

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• Are there any working implementations of the rolling hash function used in the Rabin-Karp string sea

  - by c14ppy

  I'm looking to use a rolling hash function so I can take hashes of n-grams of a very large string. For example: "stackoverflow", broken up into 5 grams would be: "stack", "tacko", "ackov", "ckove", "kover", "overf", "verfl", "erflo", "rflow" This is ideal for a rolling hash function because after I calculate the first n-gram hash, the following ones are relatively cheap to calculate because I simply have to drop the first letter of the first hash and add the new last letter of the second hash. I know that in general this hash function is generated as: H = c1ak - 1 + c2ak - 2 + c3ak - 3 + ... + cka0 where a is a constant and c1,...,ck are the input characters. If you follow this link on the Rabin-Karp string search algorithm , it states that "a" is usually some large prime. I want my hashes to be stored in 32 bit integers, so how large of a prime should "a" be, such that I don't overflow my integer? Does there exist an existing implementation of this hash function somewhere that I could already use? Here is an implementation I created: public class hash2 { public int prime = 101; public int hash(String text) { int hash = 0; for(int i = 0; i < text.length(); i++) { char c = text.charAt(i); hash += c * (int) (Math.pow(prime, text.length() - 1 - i)); } return hash; } public int rollHash(int previousHash, String previousText, String currentText) { char firstChar = previousText.charAt(0); char lastChar = currentText.charAt(currentText.length() - 1); int firstCharHash = firstChar * (int) (Math.pow(prime, previousText.length() - 1)); int hash = (previousHash - firstCharHash) * prime + lastChar; return hash; } public static void main(String[] args) { hash2 hashify = new hash2(); int firstHash = hashify.hash("mydog"); System.out.println(firstHash); System.out.println(hashify.hash("ydogr")); System.out.println(hashify.rollHash(firstHash, "mydog", "ydogr")); } } I'm using 101 as my prime. Does it matter if my hashes will overflow? I think this is desirable but I'm not sure. Does this seem like the right way to go about this?

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• Hashes vs Numeric id's

  - by Karan Bhangui

  When creating a web application that some how displays the display of a unique identifier for a recurring entity (videos on YouTube, or book section on a site like mine), would it be better to use a uniform length identifier like a hash or the unique key of the item in the database (1, 2, 3, etc). Besides revealing a little, what I think is immaterial, information about the internals of your app, why would using a hash be better than just using the unique id? In short: Which is better to use as a publicly displayed unique identifier - a hash value, or a unique key from the database? Edit: I'm opening up this question again because Dmitriy brought up the good point of not tying down the naming to db specific property. Will this sort of tie down prevent me from optimizing/normalizing the database in the future? The platform uses php/python with ISAM /w MySQL.

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• How to map hash keys to methods for an encapsulated Ruby class (tableless model)?

  - by user502052

  I am using Ruby on Rails 3 and I am tryng to map a hash (key, value pairs) to an encapsulated Ruby class (tableless model) making the hash key as a class method that returns the value. In the model file I have class Users::Account #< ActiveRecord::Base def initialize(attributes = {}) @id = attributes[:id] @firstname = attributes[:firstname] @lastname = attributes[:lastname] end end def self.to_model(account) JSON.parse(account) end My hash is hash = {\"id\":2,\"firstname\":\"Name_test\",\"lastname\":\"Surname_test\"} I can make account = Users::Account.to_model(hash) that returns (debugging) --- id: 2 firstname: Name_test lastname: Surname_test That works, but if I do account.id I get this error NoMethodError in Users/accountsController#new undefined method `id' for #<Hash:0x00000104cda410> I think because <Hash:0x00000104cda410> is an hash (!) and not the class itself. Also I think that doing account = Users::Account.to_model(hash) is not the right approach. What is wrong? How can I "map" those hash keys to class methods?

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• How do I design a cryptographic hash function?

  - by Eyal

  After reading the following about why one-way hash functions are one-way, I would like to know how to design a hash function. http://stackoverflow.com/questions/1038307/help-me-better-understand-cryptographic-hash-functions/1047106#1047106 Before everyone gets on my case: Yes, I know that it's a bad idea to not use a proven and tested hash function. I would still like to know how it's done. I'm familiar with Feistel-network ciphers but those are necessarily reversible, horrible for a cryptographic hash. Is there some sort of construction that is well-used in cryptographic hashing? Something that makes it very one-way?

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• How to only select numeric data from mysql?

  - by liuxingruo

  Does mysql have a funcion like is_num() which can allow me determine the data is numeric or not? Thanks.

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• C++ converting hexadecimal md5 hash to decimal integer

  - by Zackery

  I'm doing Elgamal Signature Scheme and I need to use the decimal hash value from the message to compute S for signature generation. string hash = md5(message); cout << hash << endl; NTL::ZZ msgHash = strtol(hash.c_str(), NULL, 16); cout << msgHash << endl; There are no integer large enough to contain the value of 32 byte hexadecimal hash, and so I tried big integer from NTL library but it didn't work out because you cannot assign long integer to NTL::ZZ type. Is there any good solution to this? I'm doing this with visual C++ in Visual Studio 2013.

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• How to sort a hash by value in descending order and output a hash in ruby?

  - by tipsywacky

  output.sort_by {|k, v| v}.reverse and for keys h = {"a"=>1, "c"=>3, "b"=>2, "d"=>4} => {"a"=>1, "c"=>3, "b"=>2, "d"=>4} Hash[h.sort] Right now I have these two. But I'm trying to sort hash in descending order by value so that it will return => {"d"=>4, "c"=>3, "b"=>2, "a"=>1 } Thanks in advance. Edit: let me post the whole code. def count_words(str) # YOUR CODE HERE output = Hash.new(0) sentence = str.gsub(/,/, "").gsub(/'/,"").gsub(/-/, "").downcase words = sentence.split() words.each do |item| output[item] += 1 end puts Hash[output.sort_by{ |_, v| -v }] return Hash[output.sort_by{|k, v| v}.reverse] end

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• MS Word Macro - Numeric field insertion with automatic calculation at end of page

  - by Will

  Hi, I am trying to duplicate a feature that exists in Multimate (Ashton Tate) word processor. Yes, the one that hasnt been supported for 20 years! If I can duplicate this one feature I can get all the users off MM and onto Word. The documents they create are billing documents. they consist of a descriptive paragraph of any length on the left side of the page, and a billing amount at the end of the paragraph over on the right hand side, like this (excuse the imperfect formatting).... +-----------------whole page--------------------+ |                                                                    | |    pppp-para 1-pppppppppp                   | |    p                                         p                   | |    p                                         p                   | |    p                                         p                   | |    p                                         p                   | |    p                                         p                   | |    p                                         p                   | |    pppppppppppppppppppp      $$$$$  | |                                                                    |  |                                                                    |  |    pppp-para 2-pppppppppp                   | |    p                                         p                   | |    p                                         p                   | |    p                                         p                   | |    p                                         p                   | |    p                                         p                   | |    p                                         p                   | |    pppppppppppppppppppp      $$$$$  | |                                                                    |  |                                                                    |  |                             etc                                  | +-----------------------------------------------------+ some of these bills can be a few hundred pages and have a dozen or so paragraphs on each page, which is why none of the users will leave MM until this efficient little feature can be duplicated. The thing that MM does really easily is that there is a function key that they can press at any time that will - - jump the cursor from the paragraph they are writing over to the right hand side - create a numeric field - allow them to enter a number into the numeric field - return them to the left hand side to start a new paragraph What MM also does is automatically total the numeric fields on each page and create a subtotal in the page footer. it also creates a total for the entire document and puts this in the footer of the last page. I would like to duplicate this feature in word with a macro, but have no idea where to start. Any suggestions or code would be great, thanks, will.

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• Rails 3 : create two dimensional hash and add values from a loop

  - by John

  I have two models : class Project < ActiveRecord::Base has_many :ticket attr_accessible .... end class Ticket < ActiveRecord::Base belongs_to :project attr_accessible done_date, description, .... end In my ProjectsController I would like to create a two dimensional hash to get in one variable for one project all tickets that are done (with done_date as key and description as value). For example i would like a hash like this : What i'm looking for : @tickets_of_project = ["done_date_1" => ["a", "b", "c"], "done_date_2" => ["d", "e"]] And what i'm currently trying (in ProjectsController) ... def show # Get current project @project = Project.find(params[:id]) # Get all dones tickets for a project, order by done_date @tickets = Ticket.where(:project_id => params[:id]).where("done_date IS NOT NULL").order(:done_date) # Create a new hash @tickets_of_project = Hash.new {} # Make a loop on all tickets, and want to complete my hash @tickets.each do |ticket| # TO DO #HOW TO PUT ticket.value IN "tickets_of_project" WITH KEY = ticket.done_date ??** end end I don't know if i'm in a right way or not (maybe use .map instead of make a where query), but how can I complete and put values in hash by checking index if already exist or not ? Thanx :)

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• Numeric operations over SHA-1 generated keys in C#

  - by webdreamer

  I'm trying to implement a Chord distributed hash table. I want to use SHA-1 as the hash function to generate node ids and map values to the DHT. However, I'll need to use numerical operations on the SHA-1 generated key, such as a modulo, for example. I wonder in which type of variable should I put the array of bytes I get, and how can I convert from one to another.

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• Implementing Two-way Binding of a Numeric Value to a String (such as TextBox.Text)

  Presents a class that facilitates high-usability binding of an ordinary TextBox to a numeric property

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• F# numeric associations

  - by b1g3ar5

  I have a numeric association for a custom type as follows: let DiffNumerics = { new INumeric<Diff> with member op.Zero = C 0.0 member op.One = C 1.0 member op.Add(a,b) = a + b member op.Subtract(a,b) = a - b member op.Multiply(a,b) = a * b member ops.Negate(a) = Diff.negate a member ops.Abs(a) = Diff.abs a member ops.Equals(a, b) = ((=) a b) member ops.Compare(a, b) = Diff.compare a b member ops.Sign(a) = int (Diff.sign a).Val member ops.ToString(x,fmt,fmtprovider) = failwith "not implemented" member ops.Parse(s,numstyle,fmtprovider) = failwith "not implemented" } GlobalAssociations.RegisterNumericAssociation(DiffNumerics) It works fine in f# interactive, but crashes when I run, because .ElementOps is not filled correctly for a matrix of these types. Any ideas why this might be? EDIT: In fsi, the code let A = dmatrix [[Diff.C 1.;Diff.C 2.;Diff.C 3.];[Diff.C 4.;Diff.C 5.;Diff.C 6.]] let B = matrix [[1.;2.;3.];[4.;5.;6.]] gives: > A.ElementOps;; val it : INumeric<Diff> = FSI_0003.NewAD+DiffNumerics@258 > B.ElementOps;; val it : INumeric<float> = Microsoft.FSharp.Math.Instances+FloatNumerics@115 > in the debugger A.ElementOps shows: '(A).ElementOps' threw an exception of type 'System.NotSupportedException' and, for the B matrix: Microsoft.FSharp.Math.Instances+FloatNumerics@115 So somehow the DiffNumerics isn't making it to the compiled program.

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• PHP hashing function not working properly

  - by Jordan Foreman

  So I read a quick PHP login system securing article, and was trying to sort of duplicate their hashing method, and during testing, am not getting the proper output. Here is my code: function decryptPassword($pw, $salt){ $hash = hash('sha256', $salt . hash('sha256', $pw)); return $hash; } function encryptPassword($pw){ $hash = hash('sha256', $pw); $salt = substr(md5(uniqid(rand(), true)), 0, 3); $hash = hash('sha265', $salt . $hash); return array( 'salt' => $salt, 'hash' => $hash ); } And here is my testing code: $pw = $_GET['pw']; $enc = encryptPassword($pw); $hash = $enc['hash']; $salt = $enc['salt']; echo 'Pass: ' . $pw . '<br />'; echo 'Hash: ' . $hash . '<br />'; echo 'Salt: ' . $salt . '<br />'; echo 'Decrypt: ' . decryptPassword($hash, $salt); Now, the output of this should be pretty obvious, but unfortunately, the $hash variable always comes out empty! I'm trying to figure out what the problem could be, and my only guess would be the second $hash assignment line in the encryptPassword(..) function. After a little testing, I've determined that the first assignment works smoothly, but the second does not. Any suggestions? Thanks SO!

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• Removing duplicates without overriding hash method

  - by Javi

  Hello, I have a List which contains a list of objects and I want to remove from this list all the elements which have the same values in two of their attributes. I had though about doing something like this: List<Class1> myList; .... Set<Class1> mySet = new HashSet<Class1>(); mySet.addAll(myList); and overriding hash method in Class1 so it returns a number which depends only in the attributes I want to consider. The problem is that I need to do a different filtering in another part of the application so I can't override hash method in this way (I would need two different hash methods). What's the most efficient way of doing this filtering without overriding hash method? Thanks

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• Out of memory hash sort in Perl

  - by syker

  I am sorting a hash in Perl. I encountered an Out of memory error when running my Perl Script: foreach $key (sort (keys(%hash))) { .... } How do I sort a hash that has tons of data?

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• Boo: Explicitly specifying the type of a hash

  - by Kiv

  I am new to Boo, and trying to figure out how to declare the type of a hash. When I do: myHash = {} myHash[key] = value (later) myHash[key].method() the compiler complains that "method is not a member of object". I gather that it doesn't know what type the value in the hash is. Is there any way I can declare to the compiler what type the keys and values of the hash are so that it won't complain?

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• iPhone: fast hash function for storing web images (url) as files (hashed filenames)

  - by Stefan Klumpp

  What is a fast hash function available for the iPhone to hash web urls (images)? I'd like to store the cached web image as a file with a hash as the filename, because I suppose the raw web url could contain strange characters that could cause problems on the file system. The hash function doesn't need to be cryptographic, but it definitely needs to be fast. Example: Input: http://www.calumetphoto.com/files/iccprofiles/icc-test-image.jpg Output: 3573ed9c4d3a5b093355b2d8a1468509 This was done by using MD5(), but since I don't know much about that topic I don't know if it is overkill (- slow).

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• Get number of times in loop over Hash object

  - by Matt Huggins

  I have an object of type Hash that I want to loop over via hash.each do |key, value|. I would like to get the number of times I've been through the loop starting at 1. Is there a method similar to each that provides this (while still providing the hash key/value data), or do I need to create another counter variable to increment within the loop?

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• Suggestions for library to hash passwords in JAVA

  - by DutrowLLC

  What JAVA library should I be using to Hash passwords for storage in a database? I was hoping to just take the plain text password, add a random salt, then store the salt and the hashed password in the database. Then when a user wanted to log in, I could just take their submitted password, add the random salt from their account information, hash it and see if it equates to the stored hash password with their account information.

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• Trying to reference a hash using a string value in Ruby

  - by Jim

  How would I refer to a hash using the value of a string - i.e. #!/usr/bin/env ruby foo = Hash.new bar = "foo" "#{bar}"["key"] = "value" results in foo:5:in `[]=': string not matched (IndexError) from foo:5 How do I use the value of bar (foo) to reference the hash named foo? Thanks!

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• csv to hash data structure conversion using perl

  - by Kavya S

  1. Convert a .csv file to perlhash data structure Format of a .csv file: sw,s1,s2,s3,s4 ver,v1,v2,v3,v4 msword,v2,v3,v1,v1 paint,v4,v2,v3,v3 outlook,v1,v1,v3,v2 my perl script: #!/usr/local/bin/perl use strict; use warnings; use Data::Dumper; my %hash; open my $fh, '<', 'some_file.csv' or die "Cannot open: $!"; while (my $line = <$fh>) { $line =~ s/,,/-/; chomp ($line); my @array = split /,/, $line; my $key = shift @array; $hash{$key} = $line; $hash{$key} = \@array; } print Dumper(\%hash); close $fh; perl hash i.e output should look like: $sw_ver_db = { s1 => { msword => {ver => v2}, paint => {ver => v4}, outlook => {ver => v1}, }, s2 => { msword => {ver => v3}, paint => {ver => v2}, outlook => {ver => v1}, }, s3 => { msword => {ver =>v1}, paint => {ver =>v3}, outlook => {ver =>v3}, }, s4 => { msword => {ver =>v1}, paint => {ver =>v3}, outlook => {ver =>v2}, }, };

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