How to detect duplicate values ​​in an array in Ruby?

Question

Let's say I have an array that looks like this:

a = [cat, dog, cat, mouse, rat, dog, cat] 

How do I get through this and do something with duplicates - for example. delete them?

In other words, if I did a.each do |i| , then how I evaluate [0], against [1], a [2], a [3] ... and then when I find the one that I want, let's say [2] in this case has the first duplicate, then I push it onto the stack or delete it or something like that.

I know how to evaluate keys as well as values ​​... but how can I evaluate values ​​against each other in the same array?

Thanks.

Answer 1

You can create a hash to store the number of repetitions of any item. Thus, iterating through the array only once.

 h = Hash.new(0) ['a','b','b','c'].each{ |e| h[e] += 1 } 

Result

  {"a"=>1, "b"=>2, "c"=>1} 

Answer 2

This works efficiently and quite simply:

 require 'set' visited = Set.new array.each do |element| if visited.include?(element) # duplicated item else # first appearance visited << element end end 

Answer 3

Try the following:

 class Array def find_dups uniq.map {|v| (self - [v]).size < (self.size - 1) ? v : nil}.compact end end a = ['cat', 'dog', 'cat', 'mouse', 'rat', 'dog', 'cat'] print a - a.find_dups # Removes duplicates 

find_dups will return items with duplicates

Answer 4

A simple solution is to run a double loop:

 a.each_with_index do |a1, idx1| a.each_with_index do |a2, idx2| next if idx1 >= idx2 # Don't compare element to itself # and don't repeat comparisons already made # do something with a pair of elements (a1, a2) end end 

If you just want to eliminate duplicates, use the method: Array#uniq .

Answer 5

Using a.uniq! to remove duplicates.

also check out ruby-doc.org where you can find more information about the methods of the ruby ​​class.

Answer 6

Try the following:

  array.inject ({}) {| h, e |  h [e] = h [e] .to_i + 1;  h}

Answer 7

This will print all duplicates in the array:

 array.inject(Hash.new(0)) { |hash,val| hash[val] += 1; hash }.each_pair { |val,count| puts "#{val} -> #{count}" if count > 1 } 

Answer 8

If you just want to get rid of duplicates, the easiest way is to take an array and an array & array. Use the and operator.

If you want to know what repetitions are, just compare the array with the array and array.

Answer 9

If the array is sorted, something like below will return only duplicates.

 array.sort.each_cons(2).select {|p| p[0] == p[1] }.map &:first 

Sorts an array, then matches it with consecutive pairs of elements, selects pairs that are the same, matches with elements.

Answer 10

The best way to do this is to compare it with a unique version of yourself. If it is the same, then it has no duplicates; if not, then there are duplicates.

 unique_array = original_array.uniq 

get a unique version of your array

 if original_array == unique_array then return true else return false 

compare it to the original array.

Simple!