I'm trying to build an array using inject. I expect consents to be an array of ParticipantConsent objects.
Each ParticipantConsent object can :have_many ParticipantConsentSample objects.
I expect sc to contain an array of arrays of ParticipantConsentSample objects associated with every ParticipantConsent object associated with a Participant.
consents = ParticipantConsent.where(:participant_id => #participant.id).all
sample_consents = consents.inject { |sc, c| sc << ParticipantConsentSample.where(:participant_consent_id => c.id).all }
Currently getting back the contents of consents when I check the contents of sample_consents. Where am I going wrong? Thanks.
Since you just want an array of arrays obtained from ParticipantConsentSample, you don't really want inject, you want map:
sample_consents = consents.map do |c|
ParticipantConsentSample.where(:participant_consent_id => c.id).all
end
try the below:
sample_consents = consents.inject([]) do |sc, c|
sc << ParticipantConsentSample.where(participant_consent_id: c.id).to_a
sc
end
If you want sample_consents to be an array, you need to initialize it as one using an argument to inject:
sample_consents = consents.inject([]) { |sc, c| ... }
Related
I have a array which is inside a hash. I want know the result of the student (pass/fail) using the following array. First I have to match them with particular standard and compare their marks with the hash pass and fails. And I want to get the key pass or fail based on their mark. How to achieve this using Ruby?
array = [
{
:standard =>1
:pass=>{:tamil=>30,:eng=>25,:math=>35},
:fail=>{:tamil=>10,:eng=>15,:maths=>20}
},
{
:standard =>2,
:pass=>{:tamil=>40,:eng=>35,:math=>45},
:fail=>{:tamil=>20,:eng=>25,:maths=>30}
}
]
#student is assumed to be defined
standard = array.select {|standard| standard[:standard] == #student.standard}
eng_pass = #student.eng_mark >= standard[:pass][:eng]
eng_fail = #student.eng_mark <= standard[:fail][:eng]
return [eng_pass, eng_fail, whatever_else_you_want]
So on and forth for various topics.
The syntax in reading values from this structure is something like:
array[0][:pass][:eng]
and accordingly you can do the comparison as usual in batch:
for i in 0..#students_array.length
num = # student's score
standard = # something like array[0][:pass][:eng]
if num > standard
# something like 'put "You passed!"'
end
end
I have a loop building a hash for use in a select field. The intention is to end up with a hash:
{ object.id => "object name", object.id => "object name" }
Using:
#hash = {}
loop_over.each do |ac|
#hash[ac.name] = ac.id
end
I think that the map method is meant for this type of situation but just need some help understanding it and how it works. Is map the right method to refactor this each loop?
Data transformations like this are better suited to each_with_object:
#hash = loop_over.each_with_object({}) { |ac, h| h[ac.name] = ac.id }
If your brain is telling you to use map but you don't want an array as the result, then you usually want to use each_with_object. If you want to feed the block's return value back into itself, then you want inject but in cases like this, inject requires a funny looking and artificial ;h in the block:
#hash = loop_over.inject({}) { |h, ac| h[ac.name] = ac.id; h }
# -------------------- yuck -----------------------------^^^
The presence of the artificial return value is the signal that you want to use each_with_object instead.
Try:
Hash[loop_over.map { |ac| [ac[:name], ac[:id]] }]
Or if you are running on Ruby 2:
loop_over.map { |ac| [ac[:name], ac[:id]] }.to_h
#hash = Hash[loop_over.map { |ac| {ac.name => ac.id} }.map(&:flatten)]
Edit, a simpler solution as per suggestion in a comment.
#hash = Hash[ loop_over.map { |ac| [ac.name, ac.id] } ]
You can simply do this by injecting a blank new Hash and performing your operation:
loop_over.inject({}){ |h, ac| h[ac.name] = ac.id; h }
Ruby FTW
No a map isn't the correct tool for this.
The general use-case of a map is to take in an array, perform an operation on each element, and spit out a (possibly) new array (not a hashmap) of the same length, with the individual element modifications.
Here's an example of a map
x = [1, 2, 3, 4].map do |i|
i+1 #transform each element by adding 1
end
p x # will print out [2, 3, 4, 5]
Your code:
#hash = {}
loop_over.each do |ac|
#hash[ac.name] = ac.id
end
There is nothing wrong with this example. You are iterating over a list, and populating a hashmap exactly as you wished.
Ruby 2.1.0 introduces brand new method to generate hashes:
h = { a: 1, b: 2, c: 3 }
h.map { |k, v| [k, v+1] }.to_h # => {:a=>2, :b=>3, :c=>4}
I would go for the inject version, but use update in the block to avoid the easy to miss (and therefore error prone) ;h suffix:
#hash = loop_over.inject({}) { |h, ac| h.update(ac.name: ac.id) }
I am using ruby-aaws to return Amazon Products and I want to enter them into my DB. I have created a model Amazonproduct and I have created a method get_amazon_data to return an array with all the product information. When i define the specific element in the array ( e.g. to_a[0] ) and then use ruby-aaws item_attributes method, it returns the name I am searching for and saves it to my DB. I am trying to iterate through the array and still have the item_attributes method work. When i don't define the element, i get this error: undefined method `item_attributes' for #Array:0x7f012cae2d68
Here is the code in my controller.
def create
#arr = Amazonproduct.get_amazon_data( :r ).to_a
#arr.each { |name|
#amazonproduct = Amazonproduct.new(params[:amazonproducts])
#amazonproduct.name = #arr.item_attributes.title.to_s
}
EDIT: Code in my model to see if that helps:
class Amazonproduct < ActiveRecord::Base
def self.get_amazon_data(r)
resp = Amazon::AWS.item_search('GourmetFood', { 'Keywords' => 'Coffee Maker' })
items = resp.item_search_response.items.item
end
end
Thanks for any help/advice.
I'm not familiar with the Amazon API, but I do observe that #arr is an array. Arrays do not usually have methods like item_attributes, so you probably lost track of which object was which somewhere in the coding process. It happens ;)
Try moving that .item_attributes call onto the object that supports that method. Maybe amazonproduct.get_amazon_data(:r), before its being turned into an array with to_a, has that method?
It's not quite clear to me what your classes are doing but to use #each, you can do something like
hash = {}
[['name', 'Macbook'], ['price', 1000]].each do |sub_array|
hash[sub_array[0]] = sub_array[1]
end
which gives you a hash like
{ 'name' => 'Macbook', 'price' => 1000 }
This hash may be easier to work with
#product = Product.new
#product.name = hash[:name]
....
EDIT
Try
def create
#arr = Amazonproduct.get_amazon_data( :r ).to_a
#arr.each do |aws_object|
#amazonproduct = Amazonproduct.new(params[:amazonproducts])
#amazonproduct.name = aws_object.item_attributes.title.to_s
end
end
Lets say I have an Array of content_categories (content_categories = user.content_categories)
I now want to add every element belonging to a certain categorie to content_categories with the category as a key and the the content-item IDs as elements of a set
In PHP something like this is possible:
foreach ($content_categories as $key => $category) {
$contentsByCategoryIDArray = Category.getContents($category[id])
$content_categories[$key][$contentsByCategoryIDArray]
}
Is there an easy way in rails to do this?
Greets,
Nico
Your question isn't really a Rails question, it's a general Ruby programming question.
Your description isn't very clear, but from what I understand, you want to group IDs for common categories using a Hash. There are various other ways of doing this, but this is easy to understand::
ary = [
'cat1', {:id => 1},
'cat2', {:id => 2},
'cat1', {:id => 3}
]
hsh = {}
ary.each_slice(2) { |a|
key,category = a
hsh[key] ? hsh[key] << category[:id] : hsh[key] = [category[:id]]
}
hsh # => {"cat1"=>[1, 3], "cat2"=>[2]}
I'm using a simple Array with a category, followed by a simple hash representing some object instance, because it makes it easy to visualize. If you have a more complex object, replace the hash entries with those objects, and tweak how you access the ID in the ternary (?:) line.
Using Enumerable.inject():
hsh = ary.each_slice(2).inject({}) { |h,a|
key,category = a
h[key] ? h[key] << category[:id] : h[key] = [category[:id]]
h
}
hsh # => {"cat1"=>[1, 3], "cat2"=>[2]}
Enumerable.group_by() could probably shrink it even more, but my brain is fading.
I'd use Enumerable#inject
content_categories = content_categories_array.inject({}){ |memo, category| memo[category] = Category.get_contents(category); memo }
Hash[content_categories.map{|cat|
[cat, Category.get_contents(cat)]
}]
Not really the right answer, because you want IDs in your array, but I post it anyway, because it's nice and short, and you might actually get away with it:
content_categories.group_by(&:category)
content_categories.each do |k,v|
content_categories[k] = Category.getContents(v)
end
I suppose it's works
If i understand correctly, content_categories is an array of categories, which needs to be turned into a hash of categories, and their elements.
content_categories_array = content_categories
content_categories_hash = {}
content_categories_array.each do |category|
content_categories_hash[category] = Category.get_contents(category)
end
content_categories = content_categories_hash
That is the long version, which you can also write like
content_categories = {}.tap do |hash|
content_categories.each { |category| hash[category] = Category.get_contents(category) }
end
For this solution, content_categories must be a hash, not an array as you describe. Otherwise not sure where you're getting the key.
contents_by_categories = Hash[*content_categories.map{|k, v| [k, Category.getContents(v.id)]}]
HI
is it possible to return an array that contains an array and hash from a method in ruby?
i.e
def something
array_new = [another_thing, another_thing_2]
hash_map = get_hash()
return [array_new, hash_map]
end
and to retrieve the array:
some_array, some_hash = something()
thanks
Sure, that's perfectly possible and works exactly as in your example.
You will only ever be able to return one thing. What you are returning there is an array containing an array and a hash.
Ruby methods can be treated as if they return multiple values so you can collect the items in an array or return them as separate objects.
def something
array_new = Array.new
hash_new = Hash.new
return array_new, hash_new
end
a, b = something
a.class # Array
b.class # Hash
c = something
c.class # Array