I have a user inputed string called x_value whose value contains something like ticker|high. Whenever there is a |, that indicates that the latter is a child of the former. The purpose of the method is to return a specific value within a hash.
sections = []
object.x_value.split('|').each do |part|
sections << part.to_sym
end
I then want to drill down the data hash and retrieve the value of the last key.
data = {"ticker":{"high":529.5,"low":465,"avg":497.25,"vol":7520812.018}}
In this example
data[sections[0]][sections[1]] returns the expected 529.5 value. However, the user may have different hashes and different levels deep of nested key/values. How can I write this?
I have tried data[sections], but that didn't work.
Use Enumerable#reduce
data = {"ticker" => {"high" => 529.5, "low" => 465,"avg" => 497.25,"vol" => 7520812.018}}
"ticker|high".split('|').reduce(data) { |dat,val| dat[val] } #=> 592.5
more example:
data = {"more_ticker" => {"ticker" => {"high" => 529.5, "low" => 465,"avg" => 497.25,"vol" => 7520812.018}}}
"more_ticker|ticker|avg".split('|').reduce(data) { |dat,val| dat[val] }
#=> 497.25
You could also use recursion:
def getit(hash, x_value)
recurse(hash, x_value.split('|'))
end
def recurse(hash, keys)
k = keys.shift
keys.empty? ? hash[k] : recurse(hash[k], keys)
end
data = {"ticker" => {"high" => 529.5, "low" => 465}}
getit(data, "ticker|high") #=> 529.5
getit(data, "ticker") #=> {"high"=>529.5, "low"=>465}
data = {"more_ticker" => {"ticker" => {"high" => 529.5, "low" => 465}}}
getit(data, "more_ticker|ticker|low") #=> 465
getit(data, "more_ticker|ticker|avg") #=> nil
Related
The idea of what I am trying to do is to clump synonym symbols to the same value, without having to redefine the same value over and over. Basically turn this:
fruits = { orange: "Citrus", grapefruit: "Citrus", tangerine: "Citrus" }
Into this:
fruits = { orange:, grapefruit:, tangerine: => "Citrus" }
What is the proper syntax for accomplishing this?
Thanks
Use a hash, in order to access the type of fruit using the fruit name. For example:
fruits = %i{ orange grapefruit tangerine apple }
citrus_fruits = %i{ orange grapefruit tangerine }
fruit_type = citrus_fruits.zip([:citrus] * citrus_fruits.length).to_h
fruit_type[:apple] = :rosaceae
puts fruit_type
# {:orange=>:citrus, :grapefruit=>:citrus, :tangerine=>:citrus, :apple=>:rosaceae}
Here, zip and to_h are used to simplify the hash creation and avoid repetitive code.
Group Keys by Value; Optionally Transform Returned Values
In Ruby, a Symbol is a core class that provides an identifier for things, and the Symbol is never duplicated during runtime. Setting aside how they're used internally, the most common use case for using a Symbol in your code is to define keys in a Hash. You can use other types of keys, but the properties of a Symbol make them especially useful as Hash keys.
With that out of the way, it looks like you're trying to group similar Hash values, but it's unclear how you expect to use this grouping. There is more than one way to do this, so I'll just pick one as an example.
Given a Hash like this one:
produce =
{
:orange => "citrus",
:grapefruit => "citrus",
:tangerine => "citrus",
:raspberry => "berry",
:strawberry => "berry",
:canteloupe => "melon",
:honeydew => "melon"
}
you can use Hash#group_by (inherited from Enumerable) to quickly sort your Hash by value. For example, using Ruby 3.0.0:
produce.group_by { _2 }
#=>
{"citrus"=>
[[:orange, "citrus"], [:grapefruit, "citrus"], [:tangerine, "citrus"]],
"berry"=>[[:raspberry, "berry"], [:strawberry, "berry"]],
"melon"=>[[:canteloupe, "melon"], [:honeydew, "melon"]]}
This returns a Hash grouped by your unique values, but you may prefer to discard the produce type in the nested Array objects. You can do that with Hash#transform_values like so:
produce.group_by { _2 }.transform_values { _1.map &:first }
#=>
{"citrus"=>[:orange, :grapefruit, :tangerine],
"berry"=>[:raspberry, :strawberry],
"melon"=>[:canteloupe, :honeydew]}
Either way, the main point is that a Hash key is associated with a value that can be of almost any class, and so you can examine the contents of each value to determine whether or not they belong to the grouping you want (which is currently defined by your key).
Your current data structure isn't really optimized for retrieving types of produce (e.g. citrus fruits) easily, but it can certainly be done. However, you may want to reconsider whether you have the right data structure for the way you want to access or manipulate your data. Your mileage will certainly vary.
Your comment about motherboards and blueprints suggest that you are given something like
h = { :mb1=>:bp3, :mb_2=>:bp1, :mb3=>:bp3, :mb4=>:bp2, :mb5=>:bp1 }
and want to produce the hash
{ :bp3=>[:mb1, :mb3], :bp1=>[:mb_2, :mb5], :bp2=>[:mb4] }
One of many ways to do that is the following:
h.each_with_object({}) { |(k,v),g| (g[v] ||= []) << k }
See Enumerable#each_with_object, and to understand why I've written the block varaiables |(k,v),g|, see array decomposition.
This is a condensed translation of the following code (which I've salted with three puts statement to show the calculations being performed):
g = {}
h.each do |key_value_pair|
k, v = key_value_pair
puts "\nkey_value_pair = #{key_value_pair}, k = #{k}, v = #{v}"
puts "g[#{v}] set to [] because g[#{v}] == nil" if g[v].nil?
g[v] = [] if g[v].nil?
g[v] << k
puts "g after g[#{v}] << #{g}"
end
#=> {:mb1=>:bp3, :mb_2=>:bp1, :mb3=>:bp3, :mb4=>:bp2, :mb5=>:bp1}
The following is displayed:
key_value_pair = [:mb1, :bp3], k = mb1, v = bp3
g[bp3] set to [] because g[bp3] == nil
g after g[bp3] << {:bp3=>[:mb1]}
key_value_pair = [:mb_2, :bp1], k = mb_2, v = bp1
g[bp1] set to [] because g[bp1] == nil
g after g[bp1] << {:bp3=>[:mb1], :bp1=>[:mb_2]}
key_value_pair = [:mb3, :bp3], k = mb3, v = bp3
g after g[bp3] << {:bp3=>[:mb1, :mb3], :bp1=>[:mb_2]}
key_value_pair = [:mb4, :bp2], k = mb4, v = bp2
g[bp2] set to [] because g[bp2] == nil
g after g[bp2] << {:bp3=>[:mb1, :mb3], :bp1=>[:mb_2], :bp2=>[:mb4]}
key_value_pair = [:mb5, :bp1], k = mb5, v = bp1
g after g[bp1] << {:bp3=>[:mb1, :mb3], :bp1=>[:mb_2, :mb5], :bp2=>[:mb4]}
#Charles Persson, if I understood your question correctly, your main goal is to refactor this snippet:
hash = {
:orange => "citrus",
:grapefruit => "citrus",
:tangerine => "citrus",
:raspberry => "berry",
:cherry => "drupe",
:strawberry => "berry",
:canteloupe => "melon",
:honeydew => "melon",
:apple => "pome"
}
to something similar to:
hash = {
[:orange, :grapefruit, :tangerine] => "citrus",
[:raspberry, :strawberry] => "berry",
:cherry => "drupe",
[:canteloupe, :honeydew] => "melon",
:apple => "pome"
}
If I am right, then I can suggest implementing a method like this one:
# source - an input hash that can contain arrays as keys.
# dest - a new output hash where all array keys are replaced by singular keys.
def mhash(source)
dest = {}
source.each_pair do |key, value|
if key.instance_of?(Array)
key.each do |sub_key|
dest[sub_key] = value
end
else
dest[key] = value
end
end
dest
end
or its shorter alternative:
def mhash(source)
source.each_pair.with_object({}) do |(key, value), dest|
key.instance_of?(Array) ? key.each { |sub_key| dest[sub_key] = value } : dest[key] = value
end
end
This way, you will be able to write a code like the following:
hash = mhash({
[:orange, :grapefruit, :tangerine] => "citrus",
[:raspberry, :strawberry] => "berry",
:cherry => "drupe",
[:canteloupe, :honeydew] => "melon",
:apple => "pome"
})
p hash
# => {
:orange => "citrus",
:grapefruit => "citrus",
:tangerine => "citrus",
:raspberry => "berry",
:strawberry => "berry",
:cherry => "drupe",
:canteloupe => "melon",
:honeydew => "melon",
:apple => "pome"
}
Otherwise, please provide a better explanation of your question. Thanks.
This question already has answers here:
Flattening nested hash to a single hash with Ruby/Rails
(6 answers)
Closed 8 years ago.
I fetch a JSON document and need to programmatically "flatten" the keys for another third-party service.
What this means is, if my JSON doc comes back with the following:
{'first_name' => "Joe", 'hoffman' => {'patterns' => ['negativity', 'self-sabotage'], 'right_road' => 'happy family'}, 'mbti' => 'INTJ'}
I need to be able to know to create a "flat" key-value pair for a third-party service like this:
first_name = "Joe"
hoffman.patterns = "negativity, self-sabotage"
hoffman.right_road = "happy family"
mbti = "INTJ"
Once I know there's a sub-document, the parsing I think I have figured out just appending the sub-keys with key + '.' + "{subkey}" but right now, don't know which ones are straight key-value and which one's have sub-documents.
Question:
a) How can I parse the JSON to know which keys have sub-documents (additional key-values)?
b) Suggestions on ways to create a string from an array
You could also monkey patch Hash to do this on it's own like so:
class Hash
def flatten_keys(prefix=nil)
each_pair.map do |k,v|
key = [prefix,k].compact.join(".")
v.is_a?(Hash) ? v.flatten_keys(key) : [key,v.is_a?(Array) ? v.join(", ") : v]
end.flatten.each_slice(2).to_a
end
def to_flat_hash
Hash[flatten_keys]
end
end
Then it would be
require 'json'
h = JSON.parse(YOUR_JSON_RESPONSE)
#=> {'first_name' => "Joe", 'hoffman' => {'patterns' => ['negativity', 'self-sabotage'], 'right_road' => 'happy family'}, 'mbti' => 'INTJ'}
h.to_flat_hash
#=> {"first_name"=>"Joe", "hoffman.patterns"=>"negativity, self-sabotage", "hoffman.right_road"=>"happy family", "mbti"=>"INTJ"}
Will work with additional nesting too
h = {"first_name"=>"Joe", "hoffman"=>{"patterns"=>["negativity", "self-sabotage"], "right_road"=>"happy family", "wrong_road"=>{"bad_choices"=>["alcohol", "heroin"]}}, "mbti"=>"INTJ"}
h.to_flat_hash
#=> {"first_name"=>"Joe", "hoffman.patterns"=>"negativity, self-sabotage", "hoffman.right_road"=>"happy family", "hoffman.wrong_road.bad_choices"=>"alcohol, heroin", "mbti"=>"INTJ"}
Quick and dirty recursive proc:
# assuming you've already `JSON.parse` the incoming json into this hash:
a = {'first_name' => "Joe", 'hoffman' => {'patterns' => ['negativity', 'self-sabotage'], 'right_road' => 'happy family'}, 'mbti' => 'INTJ'}
# define a recursive proc:
flatten_keys = -> (h, prefix = "") do
#flattened_keys ||= {}
h.each do |key, value|
# Here we check if there's "sub documents" by asking if the value is a Hash
# we also pass in the name of the current prefix and key and append a . to it
if value.is_a? Hash
flatten_keys.call value, "#{prefix}#{key}."
else
# if not we concatenate the key and the prefix and add it to the #flattened_keys hash
#flattened_keys["#{prefix}#{key}"] = value
end
end
#flattened_keys
end
flattened = flatten_keys.call a
# => "first_name"=>"Joe", "hoffman.patterns"=>["negativity", "self-sabotage"], "hoffman.right_road"=>"happy family", "mbti"=>"INTJ"}
And then, to turn the arrays into strings just join them:
flattened.inject({}) do |hash, (key, value)|
value = value.join(', ') if value.is_a? Array
hash.merge! key => value
end
# => {"first_name"=>"Joe", "hoffman.patterns"=>"negativity, self-sabotage", "hoffman.right_road"=>"happy family", "mbti"=>"INTJ"}
Another way, inspired by this post:
def flat_hash(h,f=[],g={})
return g.update({ f=>h }) unless h.is_a? Hash
h.each { |k,r| flat_hash(r,f+[k],g) }
g
end
h = { :a => { :b => { :c => 1,
:d => 2 },
:e => 3 },
:f => 4 }
result = {}
flat_hash(h) #=> {[:a, :b, :c]=>1, [:a, :b, :d]=>2, [:a, :e]=>3, [:f]=>4}
.each{ |k, v| result[k.join('.')] = v } #=> {"a.b.c"=>1, "a.b.d"=>2, "a.e"=>3, "f"=>4}
Let's say I have the following array of hashes:
h = [{"name" => "bob"}, {"car" => "toyota"}, {"age" => "25"}]
And I have the following key to match:
k = 'car'
How do I match the 'k' to 'h' and have delete every element after the match so that it returns:
h = [{"name" => "bob"}, {"car" => "toyota"}]
Just convert hash to array, do your task and then convert back
h = {"name" => "bob", "car" => "toyota", "age" => "25"}
array = h.to_a.flatten
index = array.index('car') + 1
h = Hash[*array[0..index]]
=> {"name"=>"bob", "car"=>"toyota"}
By the way, the hash is ordered only since Ruby 1.9
ar = [{"name" => "bob"}, {"car" => "toyota"}, {"age" => "25"}]
p ar[0 .. ar.index{|h| h.key?('car')}] #=>[{"name"=>"bob"}, {"car"=>"toyota"}]
I like megas' version, as its short and to the point. Another approach, which would be more explicit, would be iterating over the keys array of each hash. The keys of a hash are maintained in an ordered array (http://ruby-doc.org/core-1.9.3/Hash.html). They are ordered by when they were first entered. As a result, you can try the following:
newArray = Array.new
h.each do |hash| # Iterate through your array of hashes
newArray << hash
if hash.has_key?("car") # check if this hash is the "car" hash.
break # exits the block
end
end
This all depends, of course, on whether the array was created in the proper order. If it was, then you're golden.
A hash is unordered set by definition, so what you request is somewhat undefined. However you can do something like a hack:
h = {"name" => "bob", "car" => "toyota", "age" => "25"}
matched = false
key_given = "car"
h.each do |k,v|
if matched
h.delete(k)
end
if k == key_given
matched = true
next
end
end
I'm pretty late to the party here. I was looking for a solution to this same problem, but I didn't love these answers. So, here's my approach:
class Array
def take_until(&blk)
i = find_index &blk
take(i + 1)
end
end
h = [{"name" => "bob"}, {"car" => "toyota"}, {"age" => "25"}]
k = 'car'
h.take_until { |x| x.has_key?(k) }
=> [{"name"=>"bob"}, {"car"=>"toyota"}]
I'm trying to get the first key and value key from a hash table in ruby. I don't know the key values of the hash because it is passed to the method. I cant find anywhere online how to find the first key/value as a separate hash table.
I think hash[0] will just try to find an element with a name 0 it just returns nil when I run the code.
I know I can find the key name and the value and then create a new hash from them but i wonder if there is an easier way to do this so I get a hash right away.
here is my code:
def rps_game_winner(game)
rock_in_hash = game.invert['R']
paper_in_hash = game.invert['P']
scissors_in_hash = game.invert['S']
if(rock_in_hash)
if(paper_in_hash)
return paper_in_hash;
elsif(scissors_in_hash)
return rock_in_hash
end
elsif(paper_in_hash)
if(rock_in_hash)
return paper_in_hash
elsif(scissors_in_hash)
return scissors_in_hash
end
end
key = game.keys[-1]
value = game.values[-1]
winner = {key => value}
return winner
end
game_one = { "Bob" => 'P', "Jim" => 'P' }
puts rps_game_winner(game_one)
This gets me the correct result the problem is I don't understand why it's -1 instead of zero...
And i was hoping there was a better way to get the first key/value pair of a hash table instead of creating new hash table with the key and value you retrieved from the previous table.
You can just do
key, value = hash.first
or if you prefer:
key = hash.keys[0]
value = hash.values[0]
Then maybe:
new_hash = {key => value}
There is a shorter answer that does not require you to use extra variables:
h = { "a" => 100, "b" => 200 , "c" => 300, "d" => 400, "e" => 500}
Hash[*h.first] #=> {"a" => 100}
Or if you want to retrieve a key/value at a any single position
Hash[*h.to_a.at(1)] #=> {"b" => 200}
Or retrieve a key/values from a range of positions:
Hash[h.to_a[1,3]] #=> {"b"=>200, "c"=>300, "d"=>400}
[hash.first].to_h
Another way to do it.
my_hash = { "a" => "first", "b" => "second" }
{ my_hash.keys.first => my_hash.values.first }
This works too
Given the following code,
How would you refactor this so that the method search_word has access to issueid?
I would say that changing the function search_word so it accepts 3 arguments or making issueid an instance variable (#issueid) could be considered as an example of bad practices, but honestly I cannot find any other solution. If there's no solution aside from this, would you mind explaining the reason why there's no other solution?
Please bear in mind that it is a Ruby on Rails model.
def search_type_of_relation_in_text(issueid, type_of_causality)
relation_ocurrences = Array.new
keywords_list = {
:C => ['cause', 'causes'],
:I => ['prevent', 'inhibitors'],
:P => ['type','supersets'],
:E => ['effect', 'effects'],
:R => ['reduce', 'inhibited'],
:S => ['example', 'subsets']
}[type_of_causality.to_sym]
for keyword in keywords_list
relation_ocurrences + search_word(keyword, relation_type)
end
return relation_ocurrences
end
def search_word(keyword, relation_type)
relation_ocurrences = Array.new
#buffer.search('//p[text()*= "'+keyword+'"]/a').each { |relation|
relation_suggestion_url = 'http://en.wikipedia.org'+relation.attributes['href']
relation_suggestion_title = URI.unescape(relation.attributes['href'].gsub("_" , " ").gsub(/[\w\W]*\/wiki\//, ""))
if not #current_suggested[relation_type].include?(relation_suggestion_url)
if #accepted[relation_type].include?(relation_suggestion_url)
relation_ocurrences << {:title => relation_suggestion_title, :wiki_url => relation_suggestion_url, :causality => type_of_causality, :status => "A", :issue_id => issueid}
else
relation_ocurrences << {:title => relation_suggestion_title, :wiki_url => relation_suggestion_url, :causality => type_of_causality, :status => "N", :issue_id => issueid}
end
end
}
end
If you need additional context, pass it through as an additional argument. That's how it's supposed to work.
Setting #-type instance variables to pass context is bad form as you've identified.
There's a number of Ruby conventions you seem to be unaware of:
Instead of Array.new just use [ ], and instead of Hash.new use { }.
Use a case statement or a constant instead of defining a Hash and then retrieving only one of the elements, discarding the remainder.
Avoid using return unless strictly necessary, as the last operation is always returned by default.
Use array.each do |item| instead of for item in array
Use do ... end instead of { ... } for multi-line blocks, where the curly brace version is generally reserved for one-liners. Avoids confusion with hash declarations.
Try and avoid duplicating large chunks of code when the differences are minor. For instance, declare a temporary variable, conditionally manipulate it, then store it instead of defining multiple independent variables.
With that in mind, here's a reworking of it:
KEYWORDS = {
:C => ['cause', 'causes'],
:I => ['prevent', 'inhibitors'],
:P => ['type','supersets'],
:E => ['effect', 'effects'],
:R => ['reduce', 'inhibited'],
:S => ['example', 'subsets']
}
def search_type_of_relation_in_text(issue_id, type_of_causality)
KEYWORDS[type_of_causality.to_sym].collect do |keyword|
search_word(keyword, relation_type, issue_id)
end
end
def search_word(keyword, relation_type, issue_id)
relation_occurrences = [ ]
#buffer.search(%Q{//p[text()*= "#{keyword}'"]/a}).each do |relation|
relation_suggestion_url = "http://en.wikipedia.org#{relation.attributes['href']}"
relation_suggestion_title = URI.unescape(relation.attributes['href'].gsub("_" , " ").gsub(/[\w\W]*\/wiki\//, ""))
if (!#current_suggested[relation_type].include?(relation_suggestion_url))
occurrence = {
:title => relation_suggestion_title,
:wiki_url => relation_suggestion_url,
:causality => type_of_causality,
:issue_id => issue_id
}
occurrence[:status] =
if (#accepted[relation_type].include?(relation_suggestion_url))
'A'
else
'N'
end
relation_ocurrences << occurrence
end
end
relation_occurrences
end