Is there a method in Ruby that takes an array, and counts all unique elements and their occurrences and passes them back as a hash?

For example

  ['A','A','A','A','B','B','C'].method
> {'A' => 4, 'B' => 2, 'C' => 1}

Something like that.

['A','A','A','A','B','B','C'].group_by{|e| e}.map{|k, v| [k, v.length]}.to_h

src = ['A','A','A','A','B','B','C']
Hash[src.group_by { |x| x }.map { |k, v| [k, v.length] }]
counts = Hash.new(0)
['A','A','A','A','B','B','C'].each { |name| counts[name] += 1 }
counts => {"A"=>4, "B"=>2, "C"=>1}

['A','A','A','A','B','B','C'].each_with_object(Hash.new(0)) { |l, o| o[l] += 1 }

This is the easiest readable for me:

src = ['A','A','A','A','B','B','C']
src.group_by(&:to_s).to_a.map { |a| [a[0], a[1].count] }.to_h

Or here is another solution with reduce method:

src.reduce({}) { |b, a| b.merge({a => (b[a] || 0) + 1}) }

Or:

src.reduce(Hash.new(0)) { |b, a| b.merge({a => b[a] + 1}) }

Ruby: Count unique elements and their occurences in an array的更多相关文章

  1. [geeksforgeeks] Count the number of occurrences in a sorted array

    Count the number of occurrences in a sorted array Given a sorted array arr[] and a number x, write a ...

  2. FB面经 Prepare: Count Unique Island

    数unique island, 比如 110000 110001 001101 101100 100000 总共两个unique岛,不是四个 方法可以是记录每次新的岛屿搜索的路径,left,right ...

  3. leetcode 283 Move Zeros; 27 Remove Elements; 26 Remove Duplicated from Sorted Array;

    ,,,,}; //把数组的值赋给vector vector<int> vec(arr, arr+sizeof(arr)/sizeof(int)); 解法一: 时间复杂度O(n) 空间复杂度 ...

  4. [Algorithm] Count occurrences of a number in a sorted array with duplicates using Binary Search

    Let's say we are going to find out number of occurrences of a number in a sorted array using binary ...

  5. numpy.unique

    Find the unique elements of an array. Returns the sorted unique elements of an array. There are thre ...

  6. [Swift]LeetCode347. 前K个高频元素 | Top K Frequent Elements

    Given a non-empty array of integers, return the k most frequent elements. Example 1: Input: nums = [ ...

  7. Leetcode 347. Top K Frequent Elements

    Given a non-empty array of integers, return the k most frequent elements. For example,Given [1,1,1,2 ...

  8. 【ruby】ruby基础知识

    Install Ruby(安装) For windows you can download Ruby from http://rubyforge.org/frs/?group_id=167 for L ...

  9. Non-unique Elements

    Non-unique Elements You are given a non-empty list of integers (X). For this task, you should return ...

随机推荐

  1. 【leetcode列】3Sum

    现在的问题是,我开始思考:一是制定了一些,然后设置这个数字,除了里面找到两个数字.最后,计算和.重复,供N的数量,需要N-2周期. 我的问题是如何找到的其他两个数字,其实,我想引用Two Sum内部解 ...

  2. .net机试题总结

    1.下面是一个由*号组成的4行倒三角形图案.要求:1.输入倒三角形的行数,行数的取值3-21之间,对于非法的行数,要求抛出提示“非法行数!”:2.在屏幕上打印这个指定了行数的倒三角形. ******* ...

  3. aspx向silverlight传值

    原文:http://www.cnblogs.com/lensso/archive/2010/07/27/1785844.html 方法1: 向嵌入aspx页面的silverlight对象添加imnit ...

  4. Java中动态代理技术生成的类与原始类的区别

    用动态代理的时候,对它新生成的类长什么样子感到好奇.有幸通过一些资料消除了心里的疑惑. 平时工作使用的Spring框架里面有一个AOP(面向切面)的机制,只知道它是把类重新生成了一遍,在切面上加上了后 ...

  5. HIPO图

    HIPO图(Hierarchy Plus Input/Processing/Output)是表示软件结构的一种图形工具.以模块分解的层次性以及模块内部输入.处理.输出三大基本部分为基础建立的.它由两部 ...

  6. Codeforces 385B Bear and Strings

    题目链接:Codeforces 385B Bear and Strings 记录下每一个bear的起始位置和终止位置,然后扫一遍记录下来的结构体数组,过程中用一个变量记录上一个扫过的位置,用来去重. ...

  7. hdu1052 Tian Ji -- The Horse Racing 馋

    转载请注明出处:http://blog.csdn.net/u012860063 题目链接:pid=1052">http://acm.hdu.edu.cn/showproblem.php ...

  8. 同一时候使用windows和linux系统

    相信非常多人又想使用方便的windows,可是在开发中必须使用linux,怎样选择呢? 没关系,这里教你怎样制作双系统. 下载wubi,仅仅有几兆大,直接在windows下安装,安装好以后,双系统就制 ...

  9. HDU-2857-Mirror and Light(计算几何)

    Problem Description The light travels in a straight line and always goes in the minimal path between ...

  10. net搭建热插拔式web框架

    net搭建热插拔式web框架(重造Controller) 由于.net MVC 的controller 依赖于HttpContext,而我们在上一篇中的沙箱模式已经把一次http请求转换为反射调用,并 ...