How to print all key value pairs in Ruby hash? - ruby

My apologies for the potentially stupid question, I'm an absolute beginner to Ruby and code in general.
I have set up a hash with some predetermined values. I want to ask the user for input, if that input matches an existing key, I want the corresponding value to be updated (+ 1, in this case). Then I want to print all the current up-to-date values.
hash = {"apple": 6, "banana": 2, "carrot": 3}
order = gets.chomp.downcase
hash.each do |key, value|
if key.to_s == order
value += 1
puts "Your order includes: #{value} #{key}."
end
end
My problem is that I only know how to print a single key value pair.
E.g. if the user inputs "apple", I'd like the output to say "Your order includes: 7 apple, 2 banana, 3 carrot."

hash = {apple: 6, banana: 2, carrot: 3}
order = gets.chomp.downcase.to_sym
hash[order] = hash.fetch(order, 0) + 1
puts "Your order includes: " + hash.map { |k, v| "#{v} #{k}" }.join(", ")
Some notes:
your hash initialization hash = {"apple": 6, "banana": 2, "carrot": 3}. the keys of your hash seem strings, but if you use that syntax with the colon, they become symbols. So, you have two choice. this syntax:
hash = {"apple" => 6, "banana" => 2, "carrot" => 3}
or you can use symbols as I did and convert the user input in a symbol
what's really cool about hash is that you don't need to iterate through the elements to find what you're looking for. There's a mapping between keys and values, so it's easy find and update a value
in the third row, I'm dealing with the fact that the key could not be in the hash, I used fetch to have 0 in that case. then, I increment and I assign back to that key

The question does not specify if you want to mutate the initial hash, so I suppose you do. Then the following will do.
hash = Hash.new(0).merge(apple: 6, banana: 2, carrot: 3)
hash[gets.chomp.downcase.to_sym] += 1
puts "Your order includes: " <<
hash.map { |k, v| [v, k].join(' ') }.join(', ')
or:
puts hash.reduce("Your order includes: ") { |acc, (k, v)|
acc << "#{v} #{k}, "
}[0..-3]

Consider to initialize the hash providing a default value (Hash#default)
basket = {'apple' => 6, 'banana' => 2, 'carrot' => 3}
basket.default = 0 # <-- set default 0 for start counting new keys
Define a method to present the data:
def show(basket)
puts "Your order includes:"
basket.each{ |key, value| puts "#{value}: #{key}" }
end
Capture user input in a loop (explanation in comments):
loop do
puts "Place your order:"
order = gets.downcase.chomp # <-- format the input
break if order == '0' # <-- breaks the input loop if this contition is matched
next unless basket.has_key? order # <-- skip to next loop no matches with hash keys or remove this line if you want to count also non initialised keys
basket[order] += 1 # <-- increment by one the key
show(basket) # <-- call the metod to show the basket
end
show(basket)

Related

How to find count matching characters at the same indes and at an unmatching index

I have built a version of mastermind that checks a user's input and provides feedback based on how close the user's guess was to the winning sequence. If you're not familiar with the game, you get feedback indicating how many of your characters were guessed correctly at the same index and how many characters guessed are in the sequence, but at the wrong index. If there are duplicates in the guess, then you would not count the extra values unless they correspond to the same number of duplicates in the secret code.
Example: If the sequence is ["G","G","G","Y"] and the user guesses ["G", "Y","G","G"] then you'd want to return 2 for items at the same index and 2 for items at different indexes that are included in the secret sequence.
Another example: If the sequence is ["X","R","Y","T"] and the user guesses ["T","T","Y","Y"] then you'd return 1 for items at the same index 1 for the character guessed that is in the sequence but at the wrong index.
Anyway, to me this is not a simple problem to solve. Here's the code I used to get it to work, but it's not elegant. There must be a better way. I was hoping someone can tell me what I'm missing here?? New to Ruby...
def index_checker(input_array, sequence_array)
count = 0
leftover_input = []
leftover_sequence = []
input.each_with_index do |char, idx|
if char == sequence[idx]
count += 1
else
leftover_input << char
leftover_sequence << sequence[idx]
end
end
diff_index_checker(leftover_input, leftover_sequence, count)
end
def diff_index_checker(input, sequence, count)
count2 = 0
already_counted = []
input.each do |char|
if sequence.include?(char) && !already_counted.include?(char)
count2 += 1
already_counted << char
end
end
[count, count2]
end
Here's a clean Ruby solution, written in idiomatic Ruby object-oriented style:
class Mastermind
def initialize(input_array, sequence_array)
#input_array = input_array
#sequence_array = sequence_array
end
def matches
[index_matches, other_matches]
end
def results
[index_matches.size, other_matches.size]
end
private
attr_reader :input_array, :sequence_array
def index_matches
input_array.select.with_index { |e, i| e == sequence_array[i] }
end
def other_matches
non_exact_input & non_exact_sequence
end
def non_exact_input
array_difference(input_array, index_matches)
end
def non_exact_sequence
array_difference(sequence_array, index_matches)
end
# This method is based on https://stackoverflow.com/a/3852809/5961578
def array_difference(array_1, array_2)
counts = array_2.inject(Hash.new(0)) { |h, v| h[v] += 1; h }
array_1.reject { |e| counts[e] -= 1 unless counts[e].zero? }
end
end
You would use this class as follows:
>> input_array = ["G","G","G","Y"]
>> sequence_array = ["G", "Y","G","G"]
>> guess = Mastermind.new(input_array, sequence_array)
>> guess.results
#> [2, 2]
>> guess.matches
#> [["G", "G"], ["G", "Y"]]
Here's how it works. First everything goes into a class called Mastermind. We create a constructor for the class (which in Ruby is a method called initialize) and we have it accept two arguments: input array (the user guess), and sequence array (the answer).
We set each of these arguments to an instance variable, which is indicated by its beginning with #. Then we use attr_reader to create getter methods for #input_array and #sequence_array, which allows us to get the values by calling input_array and sequence_array from any instance method within the class.
We then define two public methods: matches (which returns an array of exact matches and an array of other matches (the ones that match but at the wrong index), and results (which returns a count of each of these two arrays).
Now, within the private portion of our class, we can define the guts of the logic. Each method has a specific job, and each is named to (hopefully) help a reader understand what it is doing.
index_matches returns a subset of the input_array whose elements match the sequence_array exactly.
other_matches returns a subset of the input_array whose elements do not match the sequence_array exactly, but do match at the wrong index.
other_matches relies on non_exact_input and non_exact_sequence, each of which is computed using the array_difference method, which I copied from another SO answer. (There is no convenient Ruby method that allows us to subtract one array from another without deleting duplicates).
Code
def matches(hidden, guess)
indices_wo_match = hidden.each_index.reject { |i| hidden[i] == guess[i] }
hidden_counts = counting_hash(hidden.values_at *indices_wo_match)
guess_counts = counting_hash(guess.values_at *indices_wo_match)
[hidden.size - indices_wo_match.size, guess_counts.reduce(0) { |tot, (k, cnt)|
tot + [hidden_counts[k], cnt].min }]
end
def counting_hash(arr)
arr.each_with_object(Hash.new(0)) { |s, h| h[s] += 1 }
end
Examples
matches ["G","G","G","Y"], ["G", "Y","G","G"]
#=> [2, 2]
matches ["X","R","Y","T"] , ["T","T","Y","Y"]
#=> [1, 1]
Explanation
The steps are as follows.
hidden = ["G","G","G","Y"]
guess = ["G", "Y","G","G"]
Save the indices i for which hidden[i] != guess[i].
indices_wo_match = hidden.each_index.reject { |i| hidden[i] == guess[i] }
#=> [1, 3]
Note that the number of indices for which the values are equal is as follows.
hidden.size - indices_wo_match.size
#=> 2
Now compute the numbers of remaining elements of guess that pair with one of the remaining values of hidden by having the same value. Begin by counting the numbers of instances of each unique element of hidden and then do the same for guess.
hidden_counts = counting_hash(hidden.values_at *indices_wo_match)
#=> {"G"=>1, "Y"=>1}
guess_counts = counting_hash(guess.values_at *indices_wo_match)
#=> {"Y"=>1, "G"=>1}
To understand how counting_hash works, see Hash::new, especially the explanation of the effect of providing a default value as an argument of new. In brief, if a hash is defined h = Hash.new(3), then if h does not have a key k, h[k] returns the default value, here 3 (the hash is not changed).
Now compute the numbers of matches of elements of guess that were not equal to the value of hidden at the same index and which pair with an element of hidden that have the same value.
val_matches = guess_counts.reduce(0) do |tot, (k, cnt)|
tot + [hidden_counts[k], cnt].min
end
#=> 2
Lastly, return the values of interest.
[hidden.size - indices_wo_match.size, val_matches]
#=> [2, 2]
In the code presented above I have substituted out the variable val_matches.
With Ruby 2.4+ one can use Enumerable#sum to replace
guess_counts.reduce(0) { |tot, (k, cnt)| tot + [hidden_counts[k], cnt].min }
with
guess_counts.sum { |k, cnt| [hidden_counts[k], cnt].min }
def judge(secret, guess)
full = secret.zip(guess).count { |s, g| s == g }
semi = secret.uniq.sum { |s| [secret.count(s), guess.count(s)].min } - full
[full, semi]
end
Demo:
> judge(["G","G","G","Y"], ["G","Y","G","G"])
=> [2, 2]
> judge(["X","R","Y","T"], ["T","T","Y","Y"])
=> [1, 1]
A shorter alternative, though I find it less clear:
full = secret.zip(guess).count(&:uniq!)
I prefer my other answer for its simplicity, but this one would be faster if someone wanted to use this for arrays larger than Mastermind's.
def judge(secret, guess)
full = secret.zip(guess).count { |s, g| s == g }
pool = secret.group_by(&:itself)
[full, guess.count { |g| pool[g]&.pop } - full]
end
Demo:
> judge(["G","G","G","Y"], ["G","Y","G","G"])
=> [2, 2]
> judge(["X","R","Y","T"], ["T","T","Y","Y"])
=> [1, 1]

How to compare and print matching hash values in Ruby?

I have two hashes like below,
h1 = {"a" => 1, "b" => 2, "c" => 3}
h2 = {"a" => 2, "b" => 2, "d" => 3}
I want to iterate over hash1 and hash2 and find matching keys and their values and print it on console.
Example here it should return output "b" => 2 .its not working with below code,
h1.each do |key1, value1|
h2.each do |key2, value2|
if ((h2.include? key1) && (h2.include? value1))
puts "matching h2 key #{h2[key2]}and h1 key #{h1[key1]}"
else
puts " don not match h2 key #{h2[key2]}and h1 key #{h1[key1]}"
end
end
end
I am from basically C++ and Java background and its very easy to do using for loops and iterators, but using Ruby, it is very difficult.
h1.merge(h2) { |k,o,n| puts "#{k}=>#{o}" if o == n }
"b" => 2
This uses the form of Hash#merge that employs a bock to determine the values of keys that are present in both hashes being merged. See the doc for details.
The second loop is not required.
h1.each do |key1, value1|
if (h2.include? key1) and (h2[key1] == value1)
puts "Match #{key1} with value #{value1}"
else
puts "#{key1} does not match"
end
end
You might write something like
h1.each do |k,v|
if h2[k] == v
puts "matched key = #{k} and value = #{v}"
else
puts "NOT matched key = #{k} and value = #{v}"
end
end
Output
NOT matched key = a and value = 1
matched key = b and value = 2
NOT matched key = c and value = 3
If the result is the main objective, select can work too:
h1.select{|k,v| h2[k] == v }

Counting the number of times a value is repeated in a Hash

I am pulling a hash from mashable.com, and I need to count instances of author names (author is the key, and the value is the author name). mashable's api
{
new: [
{
other_keys: 'other_values'...
author: 'Author's Name'
}
]
I want to iterate over the hash and pull out the author's name, and then count the amount of times it is repeated in the entire list from the mashable api.
Here is what I have; it turns the hash into an array, iterates over it, adding the count to each author name as the key, and then adds the number of repeats as the value.
This would be great, but I can't get it back into my original hash from mashable to add all of the other hash items I want to display.
all_authors = []
all_stories.each do |story|
authors = story['author']
all_authors << authors
end
counts = Hash.new(0)
all_authors.each do |name|
counts[name] += 1
end
counts.each do |key, val|
puts "#{key}: " "#{val}"
end
That does what it is supposed to, but I try to put it back into the original hash from mashable:
all_stories.each do |com|
plorf = com['comments_count'].to_i
if plorf < 1
all_stories.each do |story|
puts "Title:\n"
puts story['title']
puts "URL:\n"
puts story['short_url']
puts "Total Shares:\n"
puts story['shares']['total']
end
end
end
When I drop the code back in to that iteration, all it does is iterate of the initial has, and after each entry, I get a list of all authors and the number of stories they have written, instead of listing each author connected to the other information about each story and the number of stories they have written.
Any help is greatly appreciated.
Here's a simplified version:
h = { a: 1, b: 2, c: 1, d: 1 }
h.count { |_, v| v == 1 } #=> 3
h.values.count(1) #=> 3
Alternatively you can also group by key and then count:
h.group_by(&:last).map { |v, a| [v, a.count] }.to_h #=> {1=>3, 2=>1}
This groups the hash by its values, the counts the times elements in the array of key/value pairs. Here's a more explicit version:
grouped = h.group_by(&:last) #=> {1=>[[:a, 1], [:c, 1], [:d, 1]], 2=>[[:b, 2]]}
grouped.map { |v, a| [v, a.count] #=> [[1, 3], [2, 1]]
Then the final to_h turns the array of 2 element arrays into a hash.
#Michael Kohl it was a good answer, I think I was asking the question wrong. I wound up doing this:
author = story['author']
puts "Number of stories by #{story['author']}: #{author_count['author']}"
inside my "all_stories" loop...
yeah I am pretty sure I was trying to "re-inject" the values to the original hash, and that was way wrong...
Thanks so much for your help though

Ruby grocery list program

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.

How to determine if a record is the first/last one in an iteration?

Its a thing that made me thinking several times. In this example I have an array and this array has 10 values that should be seperated by commatas but after the last one there shouldnt be a commata so I used a counter:
data = ["john", "james", "henry", "david", "daniel", "jennifer", "ruth", "penny", "robin", "julia"]
counter = 0
count = data.size
sentence = String.new
data.each do |name|
if counter == (count-1)
sentence += name
else
sentence += "#{name}, "
end
counter += 1
end
But this is so dirty isnt there any method to find out if the current object (in this case "name") is the frist or the last one in the iteration?
in this specific case, data.join(', ') would do, more generally data.each {|d| #do stuff
unless d.equal? data.last}
You should just write data.join(', '). Anyway, answering your question:
Isn't there any method to find out if the current object is the first or the last one in the iteration?
xs = [1, 2, 3, 4]
xs.each.with_index do |x, index|
if index == 0
puts("First element: #{x}")
elsif index == xs.size - 1
puts("Last element: #{x}")
else
puts("Somewhere in the middle: #{x}")
end
end
You can use name==data.last if your array is of unique elements
Otherwise use directly
data.join(', ')

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