#product
returns a single record. By relationship this product belongs to a slot
#slot = Slot.where(['id = ?', #product.slot_id]).first
what needs to be accessed is the position x in the array of all #slots = Slot.order('id asc').all so that I can identify or iterate over the following n slots as per ruby array Class:
arr[x, n]
I am not sure I understand the question there are many methods of accessing the index for an Array e.g.
alphabet = ('a'..'z').to_a
alphabet[0]
#=> "a"
alphabet.values_at(2,3,12)
#=> ["c","d","m"]
alphabet.index('r')
#=> 17
alphabet.fetch(15)
#=> "p"
There are many more such as #at, #find_index, even #rindex which will look for the last occurance. If you need to iterate index's you can use each_index or each_with_index. Since your question does not truely explain the scenario all I can do is explain how to deal with Array indices. For a more pertinent answer please update your question to show both data and expected results.
Here is what I can gather from your question
#product = Product.find(some_id)
#slot = #product.slot
#slots = Slot.where("id > ?", #slot.id) #return all slots after the #product.slot
If want to get the Slot for a given Product you can just do this:
slot = #product.slot
assuming you have your relationships well defined.
Related
I have an array of objects and every object respond to the 'order' method.
I can write the method
objects = Objects.all
objects.each do |i|
puts i.order
end
but I'm not sure the order is correct. Is there any fast way to iterate my array following the right order of every object?
Update: real case.
class Articles < ActiveRecord::Base
as_many :article_pages
end
a = Article.find(2345)
pages = a.article_pages
pages.each ...
pages.first.order = 1
pages.last.order = 5
I need to iterate in my pages following order...
a.article_pages.order('order').each
doesn't work
By default, ActiveRecord will not guarantee any order. To change that, use:
a = Article.find(2345)
pages = a.article_pages.order('order asc')
to order by a column. Switch asc to desc to order in descending order.
You can use sort option in case you want it in ascending only
a = Article.find(2345)
pages = a.article_pages.all.sort_by &:order
I have lots of math to do on lots of data but it's all based on a few base templates. So instead of say, when doing math between 2 arrays I do this:
results = [a[0]-b[1],a[1]-b[2],a[2]-b[3]]
I want to instead just put the base template: a[0]-b[1] and make it automatically fill say 50 places in the results array. So I don't always have to manually type it.
What would be the ways to do that? And would a good way be to create 1 method that does this automatically. And I just tell it the math and it fills out an array?
I have no clue, I'm really new to programming.
a = [2,3,4]
b = [1,2,3,4]
results = a.zip(b.drop(1)).take(50).map { |v,w| v - w }
Custom
a = [2,3,4..............,1000]
b = [1,2,3,4,.............900]
class Array
def self.calculate_difference(arr1,arr2,limit)
begin
result ||= Array.new
limit.send(:times) {|index| result << arr1[index]-arr2[index+=1]}
result
rescue
raise "Index/Limit Error"
end
end
end
Call by:
Array.calculate_difference(a,b,50)
I have an Array that contains some elements multiple times. Now I want to create a new Array with one of those elements deleted.
Example:
a = [1,1,1,2]
delete_index = a.find_index(1)
result = a.clone
result.delete_at(delete_index)
# result is now [1,1,2]
This code looks really ugly for such an easy task. I had a look at the methods that Array provides, but couldn't find a better way of doing this.
a.delete_at(a.index(1) || a.length)
a.length handles the case where your element isn't found; because it's out of range, nothing will be deleted and your return value wil be nil.
If part of your question was to do this to a copy of the array, just call it on a clone:
a2 = a.clone ; a2.delete_at(...)
If you want to do this for each duplicated element, you can chain it to a block that selects the duplicated elements:
a.select { |e| array.count(e) > 1 }.each { |dup| a.delete_at a.index(dup) }
You could monkey patch Array:
class Array
def delete_first_occurrence(o)
delete_at(find_index(o) || length)
self
end
end
a = [1,1,1,2]
result = a.clone.delete_first_occurrence(1)
=> [1, 1, 2]
I can't quite tell, but it sounds like you're just trying to remove duplicates from the array. If that's the case, it's as easy as array.uniq, which will return a new array with all duplicates removed. If you'd like to modify the original array in place, you can use array.uniq! instead.
If that's not what you're trying to accomplish, please update your question with some example input and output of what you're trying to accomplish.
Ruby has a select method that takes an array and returns a subarray consisting of all the elements that pass the test given in a block:
myarray.select{|e| mytest(e)} #=> subarray of elements passing mytest
I am wondering whether there is a simple method to get not these elements, but their indices. I understand you could do this:
indices = []
myarray.each_with_index{|e,i| indices << i if mytest(e)}
But I'm looking for a one-liner. Does one exist? Please don't write an extension to the Array class, I know you can get a one-liner that way.
Another one-liner:
(0...myarray.length).select {|i| mytest(myarray[i])}
Cheers!
Here's a one-liner for you. It selects indexes of elements whose length is 3.
a = ['foo', 'bar', 't']
a.map.with_index{|el, i| i if el.length == 3}.compact # => [0, 1]
Or another one (suggested by #fl00r):
a.reduce([]){|ar,el| ar << a.index(el) if el.size == 3; ar}
Also,
myarray.select{|e| mytest(e)}.map!{|e| myarray.index(e)}
However, this won't work properly if you have any repeated elements.
I have a custom class,
class Result
end
and i want to create an array of objects from it, but i cannot figure out how to do it? Because results = Array.new creates a new array, but i cannot find where to pass the class?
Presuming I understand the question correctly, the answer is: you don't. Ruby is dynamically typed, so the array is just an array and doesn't need to know that it's going to contain objects of class Result. You can put anything into the array.
Are you looking for something like this,
class Result
end
result = Array.new(5) { Result.new }
#=> [#<Result>, #<Result>, #<Result>, #<Result>, #<Result>]
Obviously you can pass any number you want.
results = Array.new creates an empty array (as would results = [], which is more succinct). To create an array containing result objects, either create an empty array and add elements to it, or use an array literal like [element1, element2, ...].
For example results = [Result.new, Result.new, Result.new] would create an array containing three Result objects.
You should just be able to create as many Result objects as you need and append them to the array. The array can hold objects of any type.
result1 = Result.new
result2 = Result.new
result3 = Result.new
results = Array.new
results << result1
results << result2
results << result3
Your results array now has 3 Result objects in it.