hash | 易学教程

Turn an array into keys for hash

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问题 How do I turn an Array into a Hash with values of 0 without an each loop. For example, given this array: [1, 2, 3, 4] I want to get this hash: {"1"=>0, "2"=>0, "3"=>0, "4"=>0} 回答1: I'm a fan of simple, and I can never remember exactly how crazy things #inject or Hash constructor arguments work. array = [1, 2, 3, 4] hash = {} array.each do |obj| hash[obj.to_s] = 0 end puts hash.inspect # {"1"=>0, "2"=>0, "3"=>0, "4"=>0} 回答2: The standard approach is Hash[...]: Hash[xs.map { |x| [x.to_s, 0] }]

Java，该学什么？

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本人大学学的是生物技术专业，毕业后入坑Java。最近有人问我是如何转行的，需要学一些什么。我在网上看到一篇帖子，觉得写得很全。如果是我来写，可能还写不了这么全的。在此分享给网友。 2019秋招几个月累积的知识点，东西太多，懒得重整理做索引，尽量用(*)和加粗标注出高频知识点, 都是面试问过的或笔试考过的 Java基础知识(*) https://blog.csdn.net/qq_16633405/article/details/79211002 Spring Boot 启动流程(*) https://juejin.im/post/5b679fbc5188251aad213110#heading-0 Spring 一些面试题(*) https://www.ctolib.com/topics-35589.html 匿名内部类编译class(*) https://blog.csdn.net/lazyer_dog/article/details/50669473 为什么集合类没有实现Cloneable和Serializable接口？ https://www.nowcoder.com/questionTerminal/2a4902f67d5b49b6b4c05f9d7e422caf 自动装箱原理 https://www.jianshu.com/p/0ce2279c5691

How to replace all hash keys having a '.'?

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问题 I am using Ruby on Rails 4 and I would like to replace all hash keys so to change the hash from h_before = {:"aaa.bbb" => 1, :c => 2, ...} to h_after = {:bbb => 1, :c => 2, ...} That is, I would like to someway "demodulize" all hash keys having the . . How can I make that? 回答1: h_before = {:"aaa.bbb" => 1, :c => 2} h_after = h_before.inject({}){|h, (k, v)| h[k.to_s.split(".").last.to_sym] = v; h} # => {:bbb = > 1, :c => 2} 回答2: each_with_object is a cleaner and shorter approach than inject

Ruby: how to check if variable exists within a hash definition

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问题 I'm new to Ruby. Is there a way to do the following? hash = { :key1 => defined? value1 ? value1 : nil, :key2 => defined? value2 ? value2 : nil } puts hash[:key1] # outputs: ["expression"] The above code stores the expression, instead of the value (if it is defined) or nil (if it is not defined). 回答1: You're looking for lambda , or Proc . hash = { :key1 => lambda { defined?(value1) ? value1 : nil }, :key2 => lambda { defined?(value2) ? value1 : nil } } hash[:key1].call http://www.ruby-doc.org

Get key hash for release

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问题 I have been trying to get my key hash for my release to work for hours now, and I must be doing something wrong because I have searched and tried so many different things, Now lets say my alias is john_doe_key, and my keysotre is located at /Users/loaner/Downloads/UEat/app/app-release.apk I would have my command in my terminal look like this correct? keytool -exportcert -alias john_doe_key -keystore ~/Users/loaner/Downloads/UEat/app/app-release.apk | openssl sha1 -binary | openssl base64 or

PayUMoney integration - How to calculate hash for comparing with response?

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问题 Generating Hash for Post request $hashSequence = "key|txnid|amount|productinfo|firstname|email|udf1|" ."udf2|udf3|udf4|udf5|udf6|udf7|udf8|udf9|udf10"; $hashVarsSeq = explode('|', $hashSequence); $hashString = ''; foreach ($hashVarsSeq as $hashVar) { $hashString .= isset($payObject['params'][$hashVar]) ? $payObject['params'][$hashVar] : ''; $hashString .= '|'; } $hashString .= $salt; //generate hash $hash = strtolower(hash('sha512', $hashString)); After getting successful response generating

Can we implement cuckoo hashing using 1 table?

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问题 I found about Cuckoo Hash tables and they seem pretty good. But most examples code I found implement this using 2 tables. This seems to me wrong because the 2 tables may be in different memory pages and we have overhead of fetching random addresses and have no real locality. Is it not possible to use 1 array instead of 2? Is it perhaps not possible to detect when an element has already been kicked out 2 times and is time for resizing? 回答1: To answer the confusion in the comments: no this is

In Ruby, how to set a default value for a nested hash?

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问题 I recently looked for a way to correctly create and use nested hashes in Ruby. I promptly found a solution by Paul Morie, who answered his own question: hash = Hash.new { |h,k| h[k] = {} } I promptly went to use this and am glad to report it works. However, as the title says, I'd like the "secondary", "inside" hashes to return 0 by default . I'm aware that you can define the default return value of a hash both in its constructor (" Hash.new(0) ") or using .default (" hash.default(0) "). But

Sorting a hash using a method from the corresponding model

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问题 Let's say you have a model Dog with an attribute "age" a method that determines "barking frequency": class Dog < ActiveRecord::Base scope by_age, -> { order('age ASC') } def barking_frequency # some code end end In your controller you have: def index @dogs = Dog.by_age end Once you have the hash for @dogs, how can you sort it by barking_frequency, so that the result keeps the dogs of a particular age sorted together, like this: Name Age Barking Frequency Molly 2 1 Buster 2 4 Jackie 2 7 Dirk 3

smart match operator for hash of hash

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问题 I want to match keys of a hash of hash with regexp . $line=" Cluster(A,B):A(T) M(S)"; $reg="Cluster"; my ( $cluster, $characters ) = split (/:/,$line); $HoH{$cluster}={split /[( )]+/,$characters } ; foreach $value(keys %HoH){ foreach $characters (keys %{$HoH{$cluster}}){ print "$value:$characters\n" if /$reg/ ~~ %HoH; } } now Output is : Cluster(A,B):A Cluster(A,B):M This code is works fine with this sample data,but not with real data!! my data is more complicated but the structure is the