What I'm aiming to do is to create an object which is initialized with a hash and then query this object in order to get values from that hash.
To make things clearer here's a rough example of what I mean:
class HashHolder
def initialize(hash)
#hash = hash
end
def get_value(*args)
# What are my possibilities here?
end
end
holder = HashHolder.new({:a => { :b => { :c => "value" } } } )
holder.get_value(:a, :b, :c) # should return "value"
I know I can perform iteration on the arguments list as in:
def get_value(*args)
value = #hash
args.each do |k|
value = value[k]
end
return value
end
But if I plan to use this method a lot this is going to degrade my performance dramatically when all I want to do is to access a hash value.
Any suggestions on that?
To update the answer since it's been a while since it was asked.
(tested in ruby 2.3.1)
You have a hash like this:
my_hash = {:a => { :b => { :c => "value" } } }
The question asked:
my_hash.get_value(:a, :b, :c) # should return "value"
Answer: Use 'dig' instead of get_value, like so:
my_hash.dig(:a,:b,:c) # returns "value"
Since the title of the question is misleading (it should be something like: how to get a value inside a nested hash with an array of keys), here is an answer to the question actually asked:
Getting ruby hash values by an array of keys
Preparation:
my_hash = {:a => 1, :b => 3, :d => 6}
my_array = [:a,:d]
Answer:
my_hash.values_at(*my_array) #returns [1,6]
def get_value(*args)
args.inject(#hash, &:fetch)
end
In case you want to avoid iteration at lookup (which I do not feel necessary), then you need to flatten the hash to be stored:
class HashHolder
def initialize(hash)
while hash.values.any?{|v| v.kind_of?(Hash)}
hash.to_a.each{|k, v| if v.kind_of?(Hash); hash.delete(k).each{|kk, vv| hash[[*k, kk]] = vv} end}
end
#hash = hash
end
def get_value(*args)
#hash[args]
end
end
If you know the structure of the hash is always in that format you could just do:
holder[:a][:b][:c]
... returns "value".
Related
I know that if you have an array and reference it as array.uniq it will return without any of the duplicates.
However in this case it is an array of objects (is that proper ruby speak?). I want each call to go into the #calls array unless the call.from is the same as a call_formatted object already present in the array.
How can I conditionally place these objects in the array if no other objects in the array have the same call.from value?
calls_raw.each do |call|
call_formatted = {
:date => date,
:time => time,
:from => call.from,
:duration => call.duration,
:recording => recording,
}
#calls << call_formatted
end
array.uniq { |item| item[:from] }
Use #map to build your array for you and call #uniq on it...
calls_raw.map do |call|
{
:date => date,
:time => time,
:from => call.from,
:duration => call.duration,
:recording => recording,
}
end.uniq{|call| call[:from]}
The above approach will first build an array of calls larger than it may ultimately need to be, and the final call to #uniq will make the list unique.
Or, to avoid adding all the duplicates in the array, you could build it with a Hash as such:
calls_raw.each_with_object do |call, h|
h[call.from] ||= {
:date => date,
:time => time,
:from => call.from,
:duration => call.duration,
:recording => recording,
}
end.values
The Hash approach will use the first occurrence of call.from as it is being set with ||=. To use the last occurrence of call.from then use a straightforward assignment with =.
It's also been suggested to just use a Set instead of an Array.
To take that approach you're going to have to implement #eql? and #hash on the class we're populating the set with.
class CallRaw
attr_accessor :from
def initialize(from)
self.from = from
end
def eql?(o)
# Base equality on 'from'
o.from == self.from
end
def hash
# Use the hash of 'from' for our hash
self.from.hash
end
end
require 'set'
s = Set.new
=> <Set: {}>
s << CallRaw.new("Chewbaca")
=> <Set: {<CallRaw:0x00000002211888 #from="Chewbaca">}>
# We expect now, that adding another will not grow our set any larger
s << CallRaw.new("Chewbaca")
=> <Set: {<CallRaw:0x00000002211888 #from="Chewbaca">}>
# Great, it's not getting any bigger
s << CallRaw.new("Chewbaca")
s << CallRaw.new("Chewbaca")
=> <Set: {#<CallRaw:0x00000002211888 #from="Chewbaca">}>
Awesome - the Set works!!!
Now, it is interesting to note that having implemented #eql? and #hash, we can now use Array#uniq without having to pass in a block.
a = Array.new
a << CallRaw.new("Chewbaca")
=> [<CallRaw:0x000000021e2128 #from="Chewbaca">]
a << CallRaw.new("Chewbaca")
=> [<CallRaw:0x000000021e2128 #from="Chewbaca">, <CallRaw:0x000000021c2bc0 #from="Chewbaca">]
a.uniq
=> [<CallRaw:0x000000021e2128 #from="Chewbaca">]
Now, I'm just wondering if there is a badge that StackOverflow awards for having too much coffee before setting out to answer a question?
Unless there's some reason it has to be an array, I'd store the data in a Hash, keyed by the from value.
Then it's easy and fast to look up an entry by the from value. You can choose to insert a new value only if there's no value already with the same key, or insert the new value and let it replace the old entry with that key.
Example:
calls = Hash.new
def add(call)
if not calls[call.from]
calls[call.from] = call
end
end
I am using Ruby on Rails 3.2.13 and I would like to remove hash keys which corresponding hash value is blank. That is, if I have the following hash
{ :a => 0, :b => 1, :c => true, :d => "", :e => " ", :f => nil }
then the resulting hash should be (note: 0 and true are not considered blank)
{ :a => 0, :b => 1, :c => true }
How can I make that?
If using Rails you can try
hash.delete_if { |key, value| value.blank? }
or in case of just Ruby
hash.delete_if { |key, value| value.to_s.strip == '' }
There are a number of ways to accomplish this common task
reject
This is the one I use most often for cleaning up hashes as its short, clean, and flexible enough to support any conditional and doesn't mutate the original object. Here is a good article on the benefits of immutability in ruby.
hash.reject {|_,v| v.blank?}
Note: The underscore in the above example is used to indicate that we want to unpack the tuple passed to the proc, but we aren't using the first value (key).
reject!
However, if you want to mutate the original object:
hash.reject! {|_,v| v.blank?}
select
Conversely, you use select which will only return the values that return true when evaluated
hash.select {|_,v| v.present? }
select!
...and the mutating version
hash.select {|_,v| v.present? }
compact
Lastly, when you only need to remove keys that have nil values...
hash.compact
compact!
You have picked up the pattern by now, but this is the version that modifies the original hash!
hash.compact!
With respect to techvineet's solution, note the following when value == [].
[].blank? => true
[].to_s.strip == '' => false
[].to_s.strip.empty? => false
I am writing integration tests for rails and I want to compare the object created with the JSON object sent. The object returned is not exactly the same as the one sent, (i.e.) it has keys that the object sent doesn't have because I am using active model serializers to pull associations in the returned object. Basically, I just want to compare all the same keys between both objects to see if its the same. Let me know if there is a clean efficient code snippet that does this for me!
TL;DR
"Clever" test code is rarely useful. Each test should be as simple as possible, and it should be testing the behavior of some object rather than its composition. There are always ways to be clever, though.
Using Array Intersection
One unreadably-clever way to do this is to use Array#& to find the intersection of the keys, and then look for equality between the values. This will work on a relatively flat hash. For example:
hash1 = {:key1=>"value1", :key2=>"value2", :key3=>"value3", :key4=>"value4"}
hash2 = {:key1=>"value1", :key2=>"value2", :key5=>"value5"}
Array(hash1.keys & hash2.keys).map { |k| hash1[k] == hash2[k] }.uniq
#=> [true]
If you're using RSpec to test, you could say something like:
it 'has some matching key/value pairs' do
# ... populate hash1
# ... populate hash2
Array(hash1.keys & hash2.keys).
map { |k| hash1[k] == hash2[k] }.uniq.should == [true]
end
Of course, if the expectation is false, then you won't really know why, or which key/value pair was wrong. This is just one of the many reasons that you should always use fixed inputs and outputs for testing, rather than trying to do dynamic comparisons.
You could use Hash#slice, which is an Active Support core extension.
For example, if the keys you want to check are :a, :b, :c, but the result contains :a, :b, :c, :d, slice will reduce the result to just contain the keys you care about:
expected = { :a => 1, :b => 2, :c => 3 }
result = { :a => 1, :b => 2, :c => 3, :d => 4 }
result.slice(:a, :b, :c) == expected
# => true
If you get a NoMethodError: undefined method 'slice' exception, you need to require active_support/core_ext/hash/slice
First, find the keys that both hashes contain, and then compare the value for those keys:
hash1 = {:key1 => "value1", :key2 => "value2", :key3 => "value3", :key4 => "value4"}
hash2 = {:key1 => "value1", :key2 => "value2", :key5 => "value5"}
hash1_keys = hash1.keys
hash2_keys = hash2.keys
comparable_keys = hash1_keys.select{|key| hash2_keys.include?(key)}
comparable_keys.each do |key|
hash1[key].should == hash2[key]
end
I have a mongoid object:
post = Post.first
When I try:
post.attributes.each do |a|
...
end
this block parse all object attributes.
I need only parse 3 attributes. post.attr1, post.attr2, post.attr3.
whitelist = %w(attr attr2 attr3)
post.attributes.select{|el| whitelist.include?(el)}.each do |key, value|
...
end
As usual, try to abstract this.
post.attributes.except("id", "created_at", "updated_at").each do |attr|
....
end
This will also help.
You could try using the only method which returns only the attributes specified (it also adds the "_id" field), for instance:
post = Post.only(:attr_1,:attr_2).first # This will give you something like => {"_id"=>"50cf2e893428ed5437000002", "attr_1"=>value, "attr_2"=>2012-12-21 02:00:00 UTC}
post.attributes.each do |a|
next if a.first == "_id" # each `a` is an array, for instance: ["_id", "50cf2e893428ed5437000002"]
#do something with the attributes
end
I am using Ruby on Rails 3.1.0 and I would like to check if an hash is "completely" included in another hash and return a boolean value.
Say I have those hashes:
hash1 = {
:key1 => 'value1',
:key2 => 'value2',
:key3 => 'value3'
}
hash2 = {
:key1 => 'value1',
:key2 => 'value2',
:key3 => 'value3',
:key4 => 'value4',
:key5 => 'value5',
...
}
I would like to check if the hash1 is included in the hash2 even if in the hash2 there are more values than hash1 (in the above case the response that I am looking for should be true)? Is it possible to do that by using "one only code line"\"a Ruby method"?
That will be enough
(hash1.to_a - hash2.to_a).empty?
The easiest way I can think of would be:
hash2.values_at(*hash1.keys) == hash1.values
the more elegant way is to check the equality when one hash merge another.
e.g. rewrite Hash include? instance method for this.
class Hash
def include?(other)
self.merge(other) == self
end
end
{:a => 1, :b => 2, :c => 3}.include? :a => 1, :b => 2 # => true
There is a way:
hash_2 >= hash_1
Alternatively:
hash_1 <= hash_2
More info in this post: https://olivierlacan.com/posts/proposal-for-a-better-ruby-hash-include/
The most efficient and elegant solution I've found - with no intermediary arrays, or redundant loops.
class Hash
alias_method :include_key?, :include?
def include?(other)
return include_key?(other) unless other.is_a?(Hash)
other.all? do |key, value|
self[key] == value
end
end
end
Since Ruby 2.3 you can use built-in Hash#<= method.
Since Ruby 2.3, you can do this:
hash1 <= hash2
I am not sure if I understand the inclusion idea in hash.
To see if it has the same keys(usual problem).
All keys in hash1 are included in hash2:
hash1.keys - hash2.keys == []
Then if you want to compare those values do as suggested in the previous post:
hash1.values - hash2.values_at(*hash1.keys) == []