I am trying to loop an array which might look like following:
names = ['sid','john'] #this array will be dynamic, The values keep changing
I am trying to write a method where I will define an empty hash and loop the array using .each
and then store the values to hash.But not working.
def add_address
names = ['sid','john']
addr_arr = {}
names.each do |n|
addr_arr['name'] = n
end
addr_arr
end
this returns only {"name"=>"john"}.
What am I doing wrong?
The problem with your implementation is that there's only one hash and each time you set a value for the "name" key, the previous value for that key will be deleted and replaced by the new value.
I see addr_arr has arr in the name, so I assume you wanted something like this:
def add_address
names = ['sid','john']
addr_arr = []
names.each do |n|
addr_arr << { "name" => n}
end
addr_arr
end
add_address
#=> [{"name"=>"sid"}, {"name"=>"john"}]
or shorter:
['sid','john'].map{ |name| {"name" => name} }
#=> [{"name"=>"sid"}, {"name"=>"john"}]
If you always use the key 'name', you're overwriting its values every time, I don't think that's what you want. I don't know if this is what you want anyway, but this should be enough to understand the problem
names.each do |n|
addr_arr[n] = n
end
My Ruby assignment is to iterate through a hash and return the key associated with the lowest value, without using any of the following methods:
#keys #values #min #sort #min_by
I don't understand how to iterate through the hash and store each pair as it comes through, compare it to the last pair that came through, and return the lowest key. This is my code to show you my thought process, but it of course does not work. Any thoughts on how to do this? Thanks!
def key_for_min_value(name_hash)
index = 0
lowest_hash = {}
name_hash.collect do |key, value|
if value[index] < value[index + 1]
lowest = value
index = index + 1
key_for_min_value[value]
return lowest
end
end
end
Track min_value and key_for_min_value. Iterate through the hash, and any time the current value is lower than min_value, update both of these vars. At the end of the loop, return key_for_min_value.
I didn't include sample code because, hey, this is homework. :) Good luck!
One way to do it is transforming our hash into an array;
def key_for_min_value(name_hash)
# Convert hash to array
name_a = name_hash.to_a
# Default key value
d_value= 1000
d_key= 0
# Iterate new array
name_a.each do |i|
# If current value is lower than default, change value&key
if i[1] < d_value
d_value = i[1]
d_key = i[0]
end
end
return d_key
end
You might need to change d_value to something higher or find something more creative :)
We can use Enumerable#reduce method to compare entries and pick the smallest value. Each hash entry gets passed in as an array with 2 elements in reduce method, hence, I am using Array#first and Array#last methods to access key and values.
h = {"a" => 1, "b" => 2, "c" => 0}
p h.reduce{ |f, s| f.last > s.last ? s : f }.first
#=> "c"
Part of class KeyServer
#generated_keys = Hash.new
def generate_key
key = SecureRandom.urlsafe_base64
while(purged_keys.include?(key))
key = SecureRandom.urlsafe_base64
end
#add new key to hashes that maintain records
#generated_keys.merge!({key => Time.now})
#all_keys.merge!(#generated_keys) { |key, v1, v2| v1 }
return key
end
And I use the generated keys here: (I need a random pair to be selected and allotted to user)
def get_available_key
if(generated_keys.empty?)
return "404. No keys available"
else
new_key = #generated_keys.to_a.sample(1)
#generated_keys.delete(new_key[0][0].to_s)
#blocked_keys.merge!({new_key[0][0].to_s => Time.now})
end
end
This is how I use it in Sinatra
api = KeyServer.new
get '/block_key' do
api.get_available_key
end
I tried the solution mentioned in this question but when I run this as part of my Sinatra server I obtain an Internal Server Error: No implicit conversion from Array to String
How do I make this work? Any other method to obtain a random pair from a Hash would be welcome.
To get a random element from a Hash to return as a Hash you could simply patch Hash to do this like
class Hash
def sample(n)
Hash[to_a.sample(n)]
end
end
Then call like
h = {a: 1, b: 2, c: 3}
h.sample(1)
#=> {b: 2}
h.sample(2)
#=> {:b=>2, :a=>1}
Note: I used Hash::[] for compatibility purposes in Ruby 2.X you could use to_h instead.
Other than that I think there might be a few more issues with your code and it's return values.
If I were to refactor your code the sample code above would not be needed I would instead go with something like it would be something like
def get_available_key
if(generated_keys.empty?)
{"error" => "404. No keys available"}
else
new_key = #generated_keys.keys.sample(1)
#generated_keys.delete(new_key)
#blocked_keys.merge!({new_key => Time.now})[new_key]
end
end
This way it will always respond with a Hash object for handling purposes and it need not worry about multidimensional arrays at all.
I would also change the initial code to be more like this
def create_new_key
key = SecureRandom.urlsafe_base64
purged_keys.include?(key) ? create_new_key : key
end
def generate_key
key = create_new_key
#add new key to hashes that maintain records
#generated_keys.merge!({key => Time.now})
#all_keys.merge!(#generated_keys) { |key, v1, v2| v1 }
key
end
def add_to_key_chain(length)
#generated_keys ||= {}
length.times do
create_new_key
end
end
Although I don't know what the purged_keys method looks like.
hash.to_a.sample evaluates to a two-element array where the first element is some key and the second is the corresponding value.
When you call delete you should be using hash.delete(new_key[0]) instead of hash.delete(new_key[0][0].to_s).
I came across an old piece of code which was creating the hash datatype using simple arrays in ruby. I get most of it, except one part:
The point as I understand it is, every element of #store is a memory location for a particular key/value pair, as a function of the key. So #store[3] would generally store key/value pairs corresponding to key=3, key=53, ... and in general where key % size == 3 (in this case size = 50).
However, when I set hash[3] = 7, hash[53] = 9, etc., every element of #store array is populated with the key/value pairs, and not just the index 3 element. It seems like the line #store[store_key] << [key, value] in the method []=(key, value) is adding [key, value] to every element of #store, and not just one with the index store_key. Any ideas?
class SimpleHash
attr_accessor :size, :store
def initialize(size)
#size = size
#store = Array.new(size, [])
end
def []=(key, value)
store_key = key % #size
index = find_key(key, #store[store_key])
if index
#store[store_key][index][1] = value
else
p "***********************************"
p #store
#store[store_key] << [key, value]
p "after"
p store_key
p #store
end
end
end
hash = SimpleHash.new(50)
p hash
hash[3] = 5
p hash
hash[3] = 7
hash[53] = 9
hash[103] = 11
hash[104] = 11
You can simply do this
#store = Array.new(size){ [] }
Every element is a separate array.
Although your question's a bit unclear, I can guess what the problem is.
#store = Array.new(size, [])
That creates an array of the right size, but where every element is the SAME OBJECT.
Change the array-within-an-array at any position, and the change will be evident in every position.
Try instead
#store = Array.new
size.times { #store << [] }
Every sub-array will be a separate object that way.
EDIT
#nafaa boutefer's answer is better. The block gets evaluated for each instance of the array so each sub-array is a different object.
#store = Array.new(size){ [] }
I am currently learning Ruby and I'm trying to write a simple Ruby grocery_list method. Here are the instructions:
We want to write a program to help keep track of a grocery list. It takes a grocery item (like "eggs") as an argument, and returns the grocery list (that is, the item names with the quantities of each item). If you pass the same argument twice, it should increment the quantity.
def grocery_list(item)
array = []
quantity = 1
array.each {|x| quantity += x }
array << "#{quantity}" + " #{item}"
end
puts grocery_list("eggs", "eggs")
so I'm trying to figure out here how to return "2 eggs" by passing eggs twice
To help you count the different items you can use as Hash. A Hash is similar to an Array, but with Strings instead of Integers als an Index:
a = Array.new
a[0] = "this"
a[1] = "that"
h = Hash.new
h["sonja"] = "asecret"
h["brad"] = "beer"
In this example the Hash might be used for storing passwords for users. But for your
example you need a hash for counting. Calling grocery_list("eggs", "beer", "milk", "eggs")
should lead to the following commands being executed:
h = Hash.new(0) # empty hash {} created, 0 will be default value
h["eggs"] += 1 # h is now {"eggs"=>1}
h["beer"] += 1 # {"eggs"=>1, "beer"=>1}
h["milk"] += 1 # {"eggs"=>1, "beer"=>1, "milk"=>1}
h["eggs"] += 1 # {"eggs"=>2, "beer"=>1, "milk"=>1}
You can work through all the keys and values of a Hash with the each-loop:
h.each{|key, value| .... }
and build up the string we need as a result, adding
the number of items if needed, and the name of the item.
Inside the loop we always add a comma and a blank at the end.
This is not needed for the last element, so after the
loop is done we are left with
"2 eggs, beer, milk, "
To get rid of the last comma and blank we can use chop!, which "chops off"
one character at the end of a string:
output.chop!.chop!
One more thing is needed to get the complete implementation of your grocery_list:
you specified that the function should be called like so:
puts grocery_list("eggs", "beer", "milk","eggs")
So the grocery_list function does not know how many arguments it's getting. We can handle
this by specifying one argument with a star in front, then this argument will
be an array containing all the arguments:
def grocery_list(*items)
# items is an array
end
So here it is: I did your homework for you and implemented grocery_list.
I hope you actually go to the trouble of understanding the implementation,
and don't just copy-and-paste it.
def grocery_list(*items)
hash = Hash.new(0)
items.each {|x| hash[x] += 1}
output = ""
hash.each do |item,number|
if number > 1 then
output += "#{number} "
end
output += "#{item}, "
end
output.chop!.chop!
return output
end
puts grocery_list("eggs", "beer", "milk","eggs")
# output: 2 eggs, beer, milk
def grocery_list(*item)
item.group_by{|i| i}
end
p grocery_list("eggs", "eggs","meat")
#=> {"eggs"=>["eggs", "eggs"], "meat"=>["meat"]}
def grocery_list(*item)
item.group_by{|i| i}.flat_map{|k,v| [k,v.length]}
end
p grocery_list("eggs", "eggs","meat")
#=>["eggs", 2, "meat", 1]
def grocery_list(*item)
Hash[*item.group_by{|i| i}.flat_map{|k,v| [k,v.length]}]
end
grocery_list("eggs", "eggs","meat")
#=> {"eggs"=>2, "meat"=>1}
grocery_list("eggs", "eggs","meat","apple","apple","apple")
#=> {"eggs"=>2, "meat"=>1, "apple"=>3}
or as #Lee said:
def grocery_list(*item)
item.each_with_object(Hash.new(0)) {|a, h| h[a] += 1 }
end
grocery_list("eggs", "eggs","meat","apple","apple","apple")
#=> {"eggs"=>2, "meat"=>1, "apple"=>3}
Use a Hash Instead of an Array
When you want an easy want to count things, you can use a hash key to hold the name of the thing you want to count, and the value of that key is the quantity. For example:
#!/usr/bin/env ruby
class GroceryList
attr_reader :list
def initialize
# Specify hash with default quantity of zero.
#list = Hash.new(0)
end
# Increment the quantity of each item in the #list, using the name of the item
# as a hash key.
def add_to_list(*items)
items.each { |item| #list[item] += 1 }
#list
end
end
if $0 == __FILE__
groceries = GroceryList.new
groceries.add_to_list('eggs', 'eggs')
puts 'Grocery list correctly contains 2 eggs.' if groceries.list['eggs'] == 2
end
Here's a more verbose, but perhaps more readable solutions to your challenge.
def grocery_list(*items) # Notice the asterisk in front of items. It means "put all the arguments into an array called items"
my_grocery_hash = {} # Creates an empty hash
items.each do |item| # Loops over the argument array and passes each argument into the loop as item.
if my_grocery_hash[item].nil? # Returns true of the item is not a present key in the hash...
my_grocery_hash[item] = 1 # Adds the key and sets the value to 1.
else
my_grocery_hash[item] = my_grocery_hash[item] + 1 # Increments the value by one.
end
end
my_grocery_hash # Returns a hash object with the grocery name as the key and the number of occurences as the value.
end
This will create an empty hash (called dictionaries or maps in other languages) where each grocery is added as a key with the value set to one. In case the same grocery appears multiple times as a parameter to your method, the value is incremented.
If you want to create a text string and return that instead of the hash object and you can do like this after the iteration:
grocery_list_string = "" # Creates an empty string
my_grocery_hash.each do |key, value| # Loops over the hash object and passes two local variables into the loop with the current entry. Key being the name of the grocery and value being the amount.
grocery_list_string << "#{value} units of #{key}\n" # Appends the grocery_list_string. Uses string interpolation, so #{value} becomes 3 and #{key} becomes eggs. The remaining \n is a newline character.
end
return grocery_list_string # Explicitly declares the return value. You can ommit return.
Updated answer to comment:
If you use the first method without adding the hash iteration you will get a hash object back which can be used to look up the amount like this.
my_hash_with_grocery_count = grocery_list("Lemonade", "Milk", "Eggs", "Lemonade", "Lemonade")
my_hash_with_grocery_count["Milk"]
--> 1
my_hash_with_grocery_count["Lemonade"]
--> 3
Enumerable#each_with_object can be useful for things like this:
def list_to_hash(*items)
items.each_with_object(Hash.new(0)) { |item, list| list[item] += 1 }
end
def hash_to_grocery_list_string(hash)
hash.each_with_object([]) do |(item, number), result|
result << (number > 1 ? "#{number} #{item}" : item)
end.join(', ')
end
def grocery_list(*items)
hash_to_grocery_list_string(list_to_hash(*items))
end
p grocery_list('eggs', 'eggs', 'bread', 'milk', 'eggs')
# => "3 eggs, bread, milk"
It iterates an array or hash to enable building another object in a convenient way. The list_to_hash method uses it to build a hash from the items array (the splat operator converts the method arguments to an array); the hash is created so that each value is initialized to 0. The hash_to_grocery_list_string method uses it to build an array of strings that is joined to a comma-separated string.