Return string from multiple array items

Question

I have multiple arrays which have code string items in them. I need to match the code from a given string and then return a class name from the matched array.

Might be better if I show you what I've got. So below are the arrays and underneath this is the string I need to return if the given string matches an item from within the array. So lets say I send a string of '329' this should return 'ss4' as a string:

['392', '227', '179', '176']
= 'ss1'

['389', '386']
= 'ss2'

['371', '338', '335']
= 'ss3'

['368', '350', '332', '329', '323', '185', '182']
= 'ss4'

I need to know what would be the best approach for this. I could create a helper method and have an array for each code block and then check each array to see if the given string code is contained and then return the string, which could be ss1 or ss4. Is this a good idea?

What is code string item? They do not look like strings. And, class name differs for each array? What are the classes? — sawa
– sawa, Commented Apr 25, 2013 at 14:15
sorry I was being lazy as I didn't add quotes around the codes. — Peter
– Peter, Commented Apr 25, 2013 at 14:18

PinnyM · Accepted Answer · 2013-04-25 15:25:46Z

5

The most efficient approach would be to generate a translator hash once that can perform the lookup super fast:

CODES = {
  ss1: ['392', '227', '179', '176'],
  ss2: ['389', '386'],
  ss3: ['371', '338', '335'],
  ss4: ['368', '350', '332', '329', '323', '185', '182']
}

translator = CODES.each_with_object({}){|(s, a), m| a.each{|n| m[n] = s.to_s}}

Now you can simply do:

translator['329']
=> "ss4"
translator['389']
=> "ss2"

edited Apr 25, 2013 at 15:25

answered Apr 25, 2013 at 14:36

PinnyM

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4 Comments

the Tin Man Over a year ago

+1 This should be very fast and scale well. Might want to use each_with_object instead of inject though, because it tends to be cleaner with this sort of task.

Peter Over a year ago

Does the 'each_with_object' method exist when there is a match then? I like the select method that @d_ethier has done as this is much easier to read but as mentioned before this will not exit the loop even if a match is true.

PinnyM Over a year ago

@Peter, each_with_object is called once to build the translator hash. After this one time it is never called again. You then simply check against the hash to get your results.

Peter Over a year ago

@PinnyM thank you. I can see what its doing now. Also my above comment should say 'exit' not 'exist' :)

fotanus · Accepted Answer · 2013-04-25 14:21:34Z

1

def code_to_string(code)
  if [395].include? code
    "ss1"
  elsif [392, 227, 179, 176].include? code
    "ss2"
  # and so on
end

Note that the codes are integers. to match with a string code, use %w(392 227 179).include? instead of the array

answered Apr 25, 2013 at 14:21

fotanus

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4 Comments

Paul.s Over a year ago

This won't scale well at all and even with the limited cases given this method would look pretty nasty with all the branches containing long [...].include? code statements

fotanus Over a year ago

@Paul.s Most likely this lists are defined elsewhere, maybe even generated dynamically, so of course he could reuse this lists with the proper meaning in my method. But if used only here, I like better having the arrays like this instead in another place because it is easier to see what is happening (one code jump less). While the answer from @PunnyM is faster, it is way less legible. So I can't give the right answer between my and his answers because I don't know what he means by best approach

PinnyM Over a year ago

A best approach is any one that solves the problem in an efficient manner while keeping with best practices. The 'illegible' code simply turns the hash inside out - it's quite legible to me, but I guess that's subjective.

fotanus Over a year ago

@PinnyM I can read it, and perhaps so do you - the question you have to make yourself is "can my team mate read it?". Anyway, if his answer serves you best, you should pick it - I don't think you can have anything faster than a hash. I'll keep mine here as an alternative

Wally Altman · Accepted Answer · 2013-04-25 14:19:14Z

0

Here's one solution you could try:

CODE_LOOKUP = {
  [395] => 'ss1',
  [392, 227, 179, 176] => 'ss2',
  [389, 386] => 'ss3'
  # etc
}

def lookup_code(code)
  CODE_LOOKUP.each do |codes_to_test, result|
    return result if codes_to_test.include?(code)
  end
end

lookup_code(395)
# => "ss1"

lookup_code(179)
# => "ss2"

answered Apr 25, 2013 at 14:19

Wally Altman

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1 Comment

the Tin Man Over a year ago

This would slow down as the list of codes increase, especially if the targeted code is at the bottom of the hash.

Arup Rakshit · Accepted Answer · 2013-04-25 14:30:16Z

0

h = {:ss1 => [395],:ss2 => [392, 227, 179, 176] }
h.key(h.values.find{|x| x.include? "392".to_i})
#=> :ss2

edited Apr 25, 2013 at 14:30

answered Apr 25, 2013 at 14:24

Arup Rakshit

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Comments

d_ethier · Accepted Answer · 2013-04-25 14:31:17Z

0

I'd recommend joining all the arrays into a multi-dimensional hash and then searching that.

a1 = ['395']
a2 = ['392', '227', '179', '176']

h = { a1: a1, a2: a2 }
h.select {|a, v| a if v.include?('392') }.keys.first.to_s

edited Apr 25, 2013 at 14:31

answered Apr 25, 2013 at 14:13

d_ethier

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