Get item from array based on hashed string in Ruby

Question

I would like to extract an element from an array, predictably based on a string input.

My use case: Generate a color for a user, based on name.

One (faulty) implementation would be to generate a hash from the user name, and reduce it to a value between 0-25 like so:

def color
  colors = array_of_25_colors
  colors[Digest::MD5.hexdigest(name).to_i(16) & 25]
end

This implementation only returns 8 possible colors, so no good.

EDIT

Another implementation I've tried is to use the byte code from the first character in the name, but since I allow unicode in names this is not practical:

"aaron".first.bytes.first - 97
=> 0 #Okay!
"zac".first.bytes.first - 97
=> 25 #Nice!
"örjan".first.bytes.first - 97
=> 98 #Doh!

What could a working implementation look like?

bundacia · Accepted Answer · 2014-07-08T17:56:28.070

2

You can add up the ordinal values of each character in the string then divide mod 25 like this:

colors = array_of_25_colors
colors[name.bytes.reduce(:+) % 25]

edited Jul 08 '14 at 17:56

answered Jul 08 '14 at 13:39

bundacia

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Ive been using "&" thinking that was the divmod operator like a sucker!! Thanks. :) – Richard Johansson Jul 08 '14 at 13:43
using `bytes` like @theTRON suggests below makes this a little cleaner: `colors[name.bytes.reduce(:+) % 25]` – bundacia Jul 08 '14 at 14:47

score 2 · Answer 2 · answered Jul 08 '14 at 13:43

2

Building on your use of #bytes, you could also go with something like:

colors[name.bytes.inject(:+) % 25]

answered Jul 08 '14 at 13:43

theTRON

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Thanks! Just curious, why .inject(:+) instead of .sum? – Richard Johansson Jul 08 '14 at 13:44
2

@RichardJohansson `Array` does not have a built-in sum method last time I checked. It appears Rails does, though ([documentation](http://api.rubyonrails.org/classes/Enumerable.html#method-i-sum)) – Daniël Knippers Jul 08 '14 at 13:46
Ah, thanks. Not easy knowing what framework adds what methods sometimes when they feel like natural Ruby… – Richard Johansson Jul 08 '14 at 13:55

Get item from array based on hashed string in Ruby

2 Answers2