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Given I have a HUGE array, and a value from it. I want to get index of the value in array. Is there any other way, rather then call Array#index to get it? The problem comes from the need of keeping really huge array and calling Array#index enormous amount of times.
After a couple of tries I found that caching indexes inside elements by storing structs with (value, index) fields instead of the value itself gives a huge step in performance (20x times win).
Still I wonder if there's a more convenient way of finding index of en element without caching (or there's a good caching technique that will boost up the performance).
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This is mostly because the array accesses are free from the pointer analysis problem. Compilers can perfectly compute the dependency information on computations and accesses on a fixed-size array, so it can do advanced optimizations including automatic parallelization.
IndexOf(Array, Object, Int32) Searches for the specified object in a range of elements of a one-dimensional array, and returns the index of its first occurrence. The range extends from a specified index to the end of the array.
To find the index of an object in an array, by a specific property: Use the map() method to iterate over the array, returning only the value of the relevant property. Call the indexOf() method on the returned from map array. The indexOf method returns the index of the first occurrence of a value in an array.
Why not use index or rindex?
array = %w( a b c d e) # get FIRST index of element searched puts array.index('a') # get LAST index of element searched puts array.rindex('a') index: http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-index
rindex: http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-rindex
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