From: Adam Akhtar <adamtemporary@...>
Date: 2009-04-07T10:31:32+09:00
Subject: Re: how to dynamically create search term for array.find_all

Ahh sorry Robert re: eval - categories are only half of the problem. Im 
also allowing the user to filter by max and min stuff too.

So depending on what filtering options a user has set Ill have a varying 
number of conditions in my code.

So one time it could be results.find_all{|x| x.rating <= some_parameter 
&& x.rating>= some_other_parameter && etc etc etc }

Since iterating over the array only once is best for performance I 
thought it would be best to call find_all once and stuff all the 
required conditions into it. This was where i was stumped on how ot do 
that so i thought i could use eval

like so:

#conditions are collected from users choices and are stored in a hash
some_conditions = {:max_rating => 10, :min_rating => 2, :categories => 
[:horror, :scifi] }

def filter (some_films, some_conditions)

condition_string = []
condition_string.push "x.rating <= #{some_conditions[max_rating]}" if 
some_conditions[max_rating]
condition_string.push "x.rating >= #{some_conditions[min_rating}" if 
some_conditions[min_rating]

condition_string = condition_string.join(" && ")

filtered_results = some_films.find_all{|x| eval(condition_string)}

return filtered_results
end


The above code didnt filter by categories as its just for example 
purposes but I was thinking of simply calling find_all again using the 
code offered before rather than drafting up a complicated eval string 
involving && and ||. Id love ot hear how i can better this code.


-- 
Posted via http://www.ruby-forum.com/.