Intersect array of hashes with array of ids

Question

I have an array of hashes, this is not an active record model. This array is of objects of type Person with properties of id, name, age. I have a second array of strings, ["john", "james", "bill"].

I am attempting to remove all objects in the array of hashes except for the ones who have names in the second array, essentially performing an intersect, but I'm having quite a few problems. Any suggestions? I'm not sure if my syntax is just off or if I'm thinking about this the wrong way. Obviously I can just iterate through but this seems like its probably not the best way to handle the situation.

deviousdodo · Accepted Answer · 2011-10-19 21:45:36Z

2

http://www.ruby-doc.org/core-1.9.2/Array.html#method-i-select

arr1 = [{:id => 1, :name => "John"}, {:id => 2, :name => "Doe"}];
arr2 = ["Doe"];

intersect = arr1.select {|o| arr2.include? o[:name]} # you can also use select!
p intersect # outputs [{:name=>"Doe", :id=>2}]

edited Oct 19, 2011 at 21:45

answered Oct 19, 2011 at 21:39

deviousdodo

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1 Comment

Michael Kohl Over a year ago

I'd make a set out of arr2, which removes the O(n) lookup cost.

Ryan Fox · Accepted Answer · 2015-06-16 23:27:00Z

2

Late to the party, but if arr1 :name is an array this works nicely:

arr1 = [{:id => 1, :name => ["John", "Doe"]}, {:id => 2, :name => ["Doe"]}];
arr2 = ["Doe"]

> intersect = arr1.reject{|o| (arr2 & o[:name]).empty?}
=> [{:id=>1, :name=>["John", "Doe"]}, {:id=>2, :name=>["Doe"]}] #output

> arr2 = ["John"]
> intersect = arr1.reject{|o| (arr2 & o[:name]).empty?}
=> [{:id=>1, :name=>["John", "Doe"]}] #output

or use select:

intersect = arr1.select{|o| !(arr2 & o[:name]).empty?}

To remove all objects in the array of hashes except for the ones who have names in the second array, you can do:

arr1.reject!{|o| (arr2 & o[:name]).empty?}

edited Jun 16, 2015 at 23:27

answered Jun 16, 2015 at 23:18

Ryan Fox

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