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How to hash a buffer with std::hash?


How to hash a buffer with std::hash?

By : user2951349
Date : November 18 2020, 01:01 AM
To fix the issue you can do The idea with std::hash is to provide a general hashing algorithm for fixed-size data that is good enough for most uses, so users don't need to roll their own every time. The problem with variable length inputs is that hashing them is a much more complex problem, often depending on characteristics of the data itself, to require the standard library to include such an algorithm, and thus the implementation is punted to the developer. For example, a hash algorithm that works great for ASCII strings might not work so great for data containing mostly zeros, and a good algorithm for the latter might give too many collisions for strings. (There are also speed tradeoffs; some hashing algorithms might work great for everything but be too slow.)
IIRC, an old, old hashing algorithm for ASCII strings is to simply multiply every character's ASCII value together. Needless to say, this is really fast and only works because there are no zeros.
code :


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How to modify Hash to enable access of element 'hash[:a][:b]' by shorter 'hash[:a,:b]' in Ruby?

How to modify Hash to enable access of element 'hash[:a][:b]' by shorter 'hash[:a,:b]' in Ruby?


By : Andrew
Date : March 29 2020, 07:55 AM
it helps some times I would be happy to access any element of multi-dimensional hash-array by a shorter expression , I have fixed my code, so now it works
code :
class AutoHash < Hash
  def initialize *args
    super
    @update, @update_index = args[0][:update], args[0][:update_key] unless 
args.empty?
  end

    def [] key,*args
      if args.count > 0
        self[key][*args]
      else
        if self.has_key? key
          super key
        else
          AutoHash.new :update => self, :update_key => key
        end
      end
    end

    def []= *args
      v = args.pop
      k = args.shift
      if args.count > 0
        self[k][*args]= v
      else
        @update[@update_index] = self if @update and @update_index
        super k,v
      end
    end
end
a = AutoHash.new
a[:a][:b][:c] = 123
a[:a,:b,:c] = 321
p a # => {:a=>{:b=>{:c=>321}}}
h[:a][:b][:c] = 123
p h.path(:a,:b,:c) # => 123

h.path(:a,:b,:c)= 321
p h #=> {:a=>{:b=>{:c=>321}}}

mypath = [:a,:b,:c]
p h.path(mypath) #=> 321
Obtaining the hash of a file using the stream capabilities of crypto module (ie: without hash.update and hash.digest)

Obtaining the hash of a file using the stream capabilities of crypto module (ie: without hash.update and hash.digest)


By : Athira Anand
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , The crypto module of node.js (at the time of this writing at least) is not still deemed stable and so the API may change. In fact, the methods that everyone in the internet use to get the hash (md5, sha1, ...) of a file are considered legacy (from the documentation of Hash class) (note: emphasis mine): , From the quoted snippet in the question:
code :
var crypto = require('crypto');

// change to 'md5' if you want an MD5 hash
var hash = crypto.createHash('sha1');

// change to 'binary' if you want a binary hash.
hash.setEncoding('hex');

// the text that you want to hash
hash.write('hello world');

// very important! You cannot read from the stream until you have called end()
hash.end();

// and now you get the resulting hash
var sha1sum = hash.read();
var fs = require('fs');
var crypto = require('crypto');

// the file you want to get the hash    
var fd = fs.createReadStream('/some/file/name.txt');
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');

fd.on('end', function() {
    hash.end();
    console.log(hash.read()); // the desired sha1sum
});

// read all file and pipe it (write it) to the hash object
fd.pipe(hash);
For a hash of objects in ruby, hash.keys.index(obj) works but hash.has_key?(obj) does not. Why?

For a hash of objects in ruby, hash.keys.index(obj) works but hash.has_key?(obj) does not. Why?


By : Ciaron Reeder
Date : March 29 2020, 07:55 AM
hope this fix your issue First, this drove me nuts. What you're doing looked absolutely correct to me, and, as you already know, doesn't work.
I can take you part of the way to a solution:
code :
def hash
    1
end
ArgumentError: comparison of Hash with Hash failed - Sorting an array of hashes by hash name

ArgumentError: comparison of Hash with Hash failed - Sorting an array of hashes by hash name


By : Priska
Date : March 29 2020, 07:55 AM
this will help Just do as below using Enumerable#sort_by method.
code :
names = [
{"Adriana"=>{:gender=>"female", :nationality=>"danish"}},
{"Adriane"=>{:gender=>"female", :nationality=>"danish"}},
{"Agatha"=>{:gender=>"female", :nationality=>"danish"}},
{"Adrianna"=>{:gender=>"female", :nationality=>"danish"}}
]

names.sort_by { |h| h.first.first }
# => [{"Adriana"=>{:gender=>"female", :nationality=>"danish"}},
#     {"Adriane"=>{:gender=>"female", :nationality=>"danish"}},
#     {"Adrianna"=>{:gender=>"female", :nationality=>"danish"}},
#     {"Agatha"=>{:gender=>"female", :nationality=>"danish"}}]
How can I build a hash of hash from Hash of Hash of array in Ruby

How can I build a hash of hash from Hash of Hash of array in Ruby


By : user3248330
Date : March 29 2020, 07:55 AM
wish of those help I have following hash of hash of array with me: , This should work
code :
Hash[common_ids.map { |a|
  [a[0], Hash[a[1].map { |b|
    [b[0], b[1]['mac_id']]
  }]]
}]
common_ids = {"signin"=> { "company_txt"=>{"mac_id"=> "mac_id_1", "win_id"=> "win_id_1"}, "username_txtbx"=> {"mac_id"=>"mac_id_2", "win_id"=>"win_id_2"} } }
a = ["signin", { "company_txt"=>{"mac_id"=> "mac_id_1", "win_id"=> "win_id_1"}, "username_txtbx"=> {"mac_id"=>"mac_id_2", "win_id"=>"win_id_2"} }]
b = ["company_txt", {"mac_id"=> "mac_id_1", "win_id"=> "win_id_1"}]
["company_txt", "mac_id_1"]
b = ["username_txtbx", {"mac_id"=>"mac_id_2", "win_id"=>"win_id_2"}]
["username_txtbx", "mac_id_2"]
[["company_txt", "mac_id_1"], ["username_txtbx", "mac_id_2"]]
{"company_txt" => "mac_id_1", "username_txtbx" => "mac_id_2"}
["signin", {"company_txt" => "mac_id_1", "username_txtbx" => "mac_id_2"}]
[["signin", {"company_txt" => "mac_id_1", "username_txtbx" => "mac_id_2"}], ...]
{"signin" => {"company_txt" => "mac_id_1", "username_txtbx" => "mac_id_2"}, ...}
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