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I'm trying to dynamically generate a case statement based on an array of values. For example let's say I have an array of ranges
[1..3,4..6,7..20,21..38]
and I want to write a dynamic case statement that returns the first number of whatever range
case n
ranges.each do |r|
when r
r.first
end
end
Is this possible, or will I have to find another way to do it (my actual code is more complex)?
If i get your question right, then you can forget case statement and do it using detect:
ary = [1..3, 4..6, 7..20, 21..38]
num = 15 # say
ary.detect { |sub_ary| sub_ary.include?(num) }
=> 7..20
ary.detect { |sub_ary| sub_ary.include?(num) }.first # call `first` on result of above, which is a range, to get the first element.
=> 7
Just out of curiosity:
number = 5
instance_eval [
"case number",
*ranges.map { |r| "when #{r} then (#{r}).first" },
"end"
].join($/)
#⇒ 4
In addition to #detect (or #find) with #include? from Jagdeep Singhs answer you can also use the case equality operator (Range#===). This operator is used by the case statement to compare the input value with the scenario's you're providing.
ranges.find { |range| range === n }.first
Keep in mind both #detect and #find return nil if no value can be found. This means you might want to use the safe navigation operator (}&.first) to prevent a no method exception of #first on nil if the value can't be found.
Well, this works, but is kind of pointless and thread unsafe:
def get_range(n)
ranges = [1..3,4..6,7..20,21..38]
case n
when 3
# special case
199
when ->(x) { #_get_range = ranges.find { |r| r.cover?(x) } }
#_get_range.first
else
0
end
ensure
remove_instance_variable(:#_get_range) if instance_variable_defined?(:#_get_range)
end
get_range(3) # => 199
get_range(5) # => 4
get_range(50) # => 0
You could just do:
ranges.find { |r| r.cover?(n) }&.first || 0
My two cents..
ranges = [1..3,4..6,7..20,21..38]
num = 15
ranges.bsearch { |range| range.member? num }.begin
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]
What's the best way of converting a dot notation path (or even an array of strings) into a nested hash key-value? Ex: I need to convert 'foo.bar.baz' equal to 'qux' like this:
{
'foo' => {
'bar' => {
'baz' => 'qux'
}
}
}
I've done this in PHP, but I managed that by creating a key in the array and then setting a tmp variable to that array key's value by reference so any changes would also take place in the array.
Try this
f = "root/sub-1/sub-2/file"
f.split("/").reverse.inject{|a,n| {n=>a}} #=>{"root"=>{"sub-1"=>{"sub-2"=>"file"}}}
I'd probably use recursion. For example:
def hasherizer(arr, value)
if arr.empty?
value
else
{}.tap do |hash|
hash[arr.shift] = hasherizer(arr, value)
end
end
end
This results in:
> hasherizer 'foo.bar.baz'.split('.'), 'qux'
=> {"foo"=>{"bar"=>{"baz"=>"qux"}}}
I like this method below which operates on itself (or your own hash class). It'll create new hash keys or reuse/append to existing keys in a hash to add or update the value.
# set a new or existing nested key's value by a dotted-string key
def dotkey_set(dottedkey, value, deep_hash = self)
keys = dottedkey.to_s.split('.')
first = keys.first
if keys.length == 1
deep_hash[first] = value
else
# in the case that we are creating a hash from a dotted key, we'll assign a default
deep_hash[first] = (deep_hash[first] || {})
dotkey_set(keys.slice(1..-1).join('.'), value, deep_hash[first])
end
end
Usage:
hash = {}
hash.dotkey_set('how.are.you', 'good')
# => "good"
hash
# => {"how"=>{"are"=>{"you"=>"good"}}}
hash.dotkey_set('how.goes.it', 'fine')
# => "fine"
hash
# => {"how"=>{"are"=>{"you"=>"good"}, "goes"=>{"it"=>"fine"}}}
I did something similar when I wrote an HTTP server that had to move all the parameters passed in the request into a multiple value hash which might contain arrays or strings or hashes...
You can look at the code for the Plezi server and framework... although the code over there deals with values surrounded with []...
It could possibly be adjusted like so:
def add_param_to_hash param_name, param_value, target_hash = {}
begin
a = target_hash
p = param_name.split(/[\/\.]/)
val = param_value
# the following, somewhat complex line, runs through the existing (?) tree, making sure to preserve existing values and add values where needed.
p.each_index { |i| p[i].strip! ; n = p[i].match(/^[0-9]+$/) ? p[i].to_i : p[i].to_sym ; p[i+1] ? [ ( a[n] ||= ( p[i+1].empty? ? [] : {} ) ), ( a = a[n]) ] : ( a.is_a?(Hash) ? (a[n] ? (a[n].is_a?(Array) ? (a << val) : a[n] = [a[n], val] ) : (a[n] = val) ) : (a << val) ) }
rescue Exception => e
warn "(Silent): parameters parse error for #{param_name} ... maybe conflicts with a different set?"
target_hash[param_name] = param_value
end
end
This should preserve existing values while adding new values if they exist.
The long line looks something like this when broken down:
def add_param_to_hash param_name, param_value, target_hash = {}
begin
# a will hold the object to which we Add.
# As we walk the tree we change `a`. we start at the root...
a = target_hash
p = param_name.split(/[\/\.]/)
val = param_value
# the following, somewhat complex line, runs through the existing (?) tree, making sure to preserve existing values and add values where needed.
p.each_index do |i|
p[i].strip!
# converts the current key string to either numbers or symbols... you might want to replace this with: n=p[i]
n = p[i].match(/^[0-9]+$/) ? p[i].to_i : p[i].to_sym
if p[i+1]
a[n] ||= ( p[i+1].empty? ? [] : {} ) # is the new object we'll add to
a = a[n] # move to the next branch.
else
if a.is_a?(Hash)
if a[n]
if a[n].is_a?(Array)
a << val
else
a[n] = [a[n], val]
end
else
a[n] = val
end
else
a << val
end
end
end
rescue Exception => e
warn "(Silent): parameters parse error for #{param_name} ... maybe conflicts with a different set?"
target_hash[param_name] = param_value
end
end
Brrr... Looking at the code like this, I wonder what I was thinking...
I am trying to change numbers up to 100 from integers into words, but have run into some trouble, can anyone point out what is missing with my code:
def in_words(integer)
numWords = {
0=>"zero",
1=>"one",
2=>"two",
3=>"three",
4=>"four",
5=>"five",
6=>"six",
7=>"seven",
8=>"eight",
9=>"nine",
10=>"ten",
11=>"eleven",
12=>"twelve",
13=>"thirteen",
14=>"fourteen",
15=>"fifteen",
16=>"sixteen",
17=>"seventeen",
18=>"eighteen",
19=>"nineteen",
20=>"twenty",
30=>"thirty",
40=>"fourty",
50=>"fifty",
60=>"sixty",
70=>"seventy",
80=>"eighty",
90=>"ninety",
100=>"one hundred"
}
array = integer.to_s.split('')
new_array = []
numWords.each do |k,v|
array.each do |x|
if x = k
new_array.push(v)
end
end
end
new_array.join('')
end
Right now when I do:
inwords(0)
I get the following:
=>"zeroonetwothreefourfivesixseveneightnineteneleventwelvethirteenfourteenfiftee nsixteenseventeeneighteennineteentwentythirtyfourtyfiftysixtyseventyeightyninetyone hundred"
Edit
I noticed your code iterates through the array a lot of times and uses the = instead of the == in your if statements.
Your code could be more efficient using the Hash's #[] method in combination with the #map method.., here's a one-line alternative:
integer.to_s.split('').map {|i| numWords[i.to_i]} .join ' '
Also, notice that the integer.to_s.split('') will split the array into one-digit strings, so having numbers up to a hundred isn't relevant for the code I proposed.
To use all the numbers in the Hash, you might want to use a Regexp to identify the numbers you have. One way is to do the following (I write it in one line, but it's easy to break it down using variable names for each step):
integer.to_s.gsub(/(\d0)|([1]?\d)/) {|v| v + " "} .split.map {|i| numWords[i.to_i]} .join ' '
# or:
integer.to_s.gsub(/(#{numWords.keys.reverse.join('|')})/) {|v| v + " "} .split.map {|i| numWords[i.to_i]} .join ' '
# out = integer.to_s
# out = out.gsub(/(#{numWords.keys.reverse.join('|')})/) {|v| v + " "}
# out = out.split
# out = out.map {|i| numWords[i.to_i]}
# out = out.join ' '
Edit 2
Since you now mention that you want the method to accept numbers up to a hundred and return the actual number (23 => twenty three), maybe a different approach should be taken... I would recommend that you update your question as well.
def in_words(integer)
numWords = {
0=>"zero",
1=>"one",
2=>"two",
3=>"three",
4=>"four",
5=>"five",
6=>"six",
7=>"seven",
8=>"eight",
9=>"nine",
10=>"ten",
11=>"eleven",
12=>"twelve",
13=>"thirteen",
14=>"fourteen",
15=>"fifteen",
16=>"sixteen",
17=>"seventeen",
18=>"eighteen",
19=>"nineteen",
20=>"twenty",
30=>"thirty",
40=>"fourty",
50=>"fifty",
60=>"sixty",
70=>"seventy",
80=>"eighty",
90=>"ninety",
100=>"one hundred"
}
raise "cannot accept such large numbers" if integer > 100
raise "cannot accept such small numbers" if integer < 0
return "one hundred" if integer == 100
if integer < 20 || integer %10 == 0
numWords[integer]
else
[numWords[integer / 10 * 10], numWords[integer % 10]].join ' '
end
end
the integer / 10 * 10 makes the number a round number (ten, twenty, etc') because integers don't have fractions (so, 23/10 == 2 and 2 * 10 == 20). The same could be achieved using integer.round(-1), which is probably better.
It seems like all you're trying to do is find a mapping from an implicit hash
module NumWords
INT2STR = {
0=>"zero",
1=>"one",
2=>"two",
3=>"three",
4=>"four",
5=>"five",
6=>"six",
7=>"seven",
8=>"eight",
9=>"nine",
10=>"ten",
11=>"eleven",
12=>"twelve",
13=>"thirteen",
14=>"fourteen",
15=>"fifteen",
16=>"sixteen",
17=>"seventeen",
18=>"eighteen",
19=>"nineteen",
20=>"twenty",
30=>"thirty",
40=>"fourty",
50=>"fifty",
60=>"sixty",
70=>"seventy",
80=>"eighty",
90=>"ninety",
100=>"one hundred"
}
module_function
def in_words(integer)
INT2STR[integer]
end
end
The above code separates the hash definition from the method call so that the hash doesn't get recreated every time you call in_words.
You can also use Hash#fetch instead of Hash#[] as Andrey pointed out.
Your test whether x = k is your first problem (in two ways).
Firstly, if x = k means assign the value of k to x and then execute the if block if that value is true (basically anything other than false or nil).
What you should actually be testing is x == k which will return true if x is equal to k.
The second problem is that you converted your number into an array of string representation so you are comparing, for example, if "0" == 0. This won't return true because they are different types.
If you convert it to if x.to_i == k then your if block will be executed and you'll get:
> in_words(0)
=> "zero"
Then you get to move onto the next problem which is that you're looking at your number digit by digit and some of the values you are testing against need two digits to be recognised:
> in_words(10)
=> "zeroone"
You might be in looking at a different question then - or maybe that is the question you wanted answered all along!
Here's another way you might do it:
ONES_TO_TEXT = { 0=>"zero", 1=>"one", 2=>"two", 3=>"three", 4=>"four",
5=>"five", 6=>"six", 7=>"seven", 8=>"eight", 9=>"nine" }
TEENS_TO_TEXT = { 10=>"ten", 11=>"eleven", 12=>"twelve",
13=>"thirteen", 15=>"fifteen" }
TENS_TO_TEXT = { 2=>"twenty", 3=>"thirty", 5=>"fifty", 8=>"eighty" }
def in_words(n)
raise ArgumentError, "#{n} is out-of_range" unless (0..100).cover?(n)
case n.to_s.size
when 1 then ONES_TO_TEXT[n]
when 3 then "one hundred"
else
case n
when (10..19)
TEENS_TO_TEXT.key?(n) ? TEENS_TO_TEXT[n] : ONES_TO_TEXT[n]+"teen"
else
t,o = n.divmod(10)
(TENS_TO_TEXT.key?(t) ? TENS_TO_TEXT[t] : ONES_TO_TEXT[t]+"ty") +
(o.zero? ? '' : "-#{ONES_TO_TEXT[o]}")
end
end
end
Let's try it:
in_words(5) #=> "five"
in_words(10) #=> "ten"
in_words(15) #=> "fifteen"
in_words(20) #=> "twenty"
in_words(22) #=> "twenty-two"
in_words(30) #=> "thirty"
in_words(40) #=> "fourty"
in_words(45) #=> "fourty-five"
in_words(50) #=> "fifty"
in_words(80) #=> "eighty"
in_words(99) #=> "ninety-nine"
in_words(100) #=> "one hundred"
Here the increased complexity may not be justified, but this approach may in fact simplify the calculations when the maximum permitted value of n is much greater than 100.
My question is whether I can use a range as the value in a key:value pair in a hash. I am working on a problem where I am trying to return a letter grade (A-F) for an average of numerical grades (array of numbers). I have a working solution, but I came across something intriguing. Here is my code:
def get_grade(array)
avg = (array.inject {|num, x| num + x}) / array.length
grades = {
"A" => [90..10]
"B" => [80..89],
"C" => [70..79],
"D" => [60..69],
"F" => [0..59],
}
grades.default = "Error"
puts grades.key(avg)
end
arraya = [100,90,100,99,99]
puts get_grade(arraya)
I know I could return the letter grade with either a case or an if statement. It seems like I should be able to use a hash instead but it doesn't work. Why can't I set up a hash with a range as value? Thanks.
You could use a case statement:
def get_grade(scores)
case scores.inject(&:+) / scores.length
when 90..100; 'A'
when 80..89; 'B'
when 70..79; 'C'
when 60..69; 'D'
when 0..59; 'F'
else; 'Error'
end
end
arraya = [100,90,100,99,99]
puts get_grade(arraya)
#=> A
You may want to rewrite your method as the following:
def get_grade(array)
avg = array.inject(:+) / array.length
grades = {
"A" => (90..100),
"B" => (80..89),
"C" => (70..79),
"D" => (60..69),
"F" => (0..59),
}
grade = grades.find{|key, range| range.include?(avg) }
grade.nil? ? "Unknown" : grade.first
end
arraya = [100,90,100,99,99]
puts get_grade(arraya) # => A