Passing procs and methods - ruby

I came across this code:
squareIt = Proc.new do |x|
x * x
end
doubleIt = Proc.new do |x|
x + x
end
def compose proc1, proc2
Proc.new do |x|
proc2.call(proc1.call(x))
end
end
doubleThenSquare = compose(doubleIt, squareIt)
squareThenDouble = compose(squareIt, doubleIt)
doubleThenSquare.call(5)
squareThenDouble.call(5)
doubleThenSquare is called with 5. doubleThenSquare is equal to the return value of compose, which has its two parameters doubleIt and squareIt passed.
I don't see how 5 is passed all its way into the different procs Proc.new do |x|. How does it know what x is in each case?


Let's step through it.
doubleIt = Proc.new do |x|
x + x
end
#=> #<Proc:0x00000002326e08#(irb):1429>
squareIt = Proc.new do |x|
x * x
end
#=> #<Proc:0x00000002928bf8#(irb):1433>
proc1 = doubleIt
proc2 = squareIt
compose returns the proc proc3.
proc3 = Proc.new do |x|
proc2.call(proc1.call(x))
end
#=> #<Proc:0x000000028e7608#(irb):1445>
proc3.call(x) is executed in the same way as
proc3_method(x)
where
def proc3_method(x)
y = proc1.call(x)
proc2.call(y)
end
When x = 5,
y = proc1.call(5)
#=> 10
proc2.call(10)
#=> 100
proc3_method(5) therefore returns 100, as does proc3.call(5).

Related

Is there a Ruby method for determining if all instance variables of two instances of the same class are equal?

Is there a Ruby method for comparing two objects based on whether all of their instance variables are equal? The method would behave like this code.
class Coordinates
attr_reader :x, :y
def initialize(x, y)
#x = x
#y = y
end
end
coordinates1 = Coordinates.new(0, 0)
coordinates2 = Coordinates.new(0, 0)
coordinates3 = Coordinates.new(1, 0)
compare(coordinates1, coordinates1) # => true
compare(coordinates1, coordinates2) # => true
compare(coordinates1, coordinates3) # => false
Does this method or something similar exist?

There is no built-in method for this, but you could quite easily write one. However, I think you're asking an XY question.
Here is what I think the question is supposed to say:
How should I define a method to check that two Coordinates instances are equal?
And here's my answer:
Define a custom == method:
class Coordinates
attr_reader :x, :y
def initialize(x, y)
#x = x
#y = y
end
def ==(other)
return super unless other.is_a?(Coordinates)
x == other.x && y == other.y
end
end
...But in the spirit of StackOverflow, here's some meta-programming to check whether all instance variables have the same name and value:
# returns true if all objects have the same instance variable names and values
def compare(*objects)
objects.map do |object|
object.instance_variables.map do |var_name|
[var_name, object.instance_variable_get(var_name)]
end
end.uniq.count == 1
end

Case 1
class A
def initialize(x,y)
#x = x
#y = y
end
def m
#x = 5
#y = 6
end
end
a1 = A.new(1,2)
#=> #<A:0x00005d22a3878048 #x=1, #y=2>
a1.m
a1 #=> #<A:0x00005d22a3878048 #x=5, #y=6>
a2 = A.new(3,4)
#=> #<A:0x00005d22a38b5330 #x=3, #y=4>
a2.m
a2 #=> #<A:0x00005d22a38b5330 #x=5, #y=6>
Then,
a1.instance_variables.all? { |e|
a1.instance_variable_get(e) == a2.instance_variable_get(e) }
#=> true
tells us that the values of #x and the values of #y are the same for both instances.
Case 2
Now let's change the code so that another instance variable is added conditionally.
class A
def initialize(x,y)
#x = x
#y = y
end
def m
#z = 3 if #x == 3
#x = 5
#y = 6
end
end
a1 = A.new(1,2)
#=> #<A:0x000057d1fd563c78 #x=1, #y=2>
a1.m
a1 #=> #<A:0x000057d1fd27f200 #x=5, #y=6>
a2 = A.new(3,4)
#=> #<A:0x000057d1fd57cb38 #x=3, #y=4>
a2.m
a2 #=> #<A:0x000057d1fd2f9e10 #x=5, #y=6, #z=3>
At this point are all instance variables of one of these instances equal to the corresponding instance variable of the other instance? No, because a2 has an additional instance variable, #z. Therefore,
a1.instance_variables.all? { |e|
a1.instance_variable_get(e) == a2.instance_variable_get(e) }
#=> true
gives the wrong answer, for obvious reasons. Perhaps we could test as follows:
a1.instance_variables.all? { |e|
a1.instance_variable_get(e) == a2.instance_variable_get(e) } &&
a2.instance_variables.all? { |e|
a1.instance_variable_get(e) == a2.instance_variable_get(e) }
#=> true && false => false
This has a gotcha, however, if #z equals nil.
Case 3
class A
def initialize(x,y)
#x = x
#y = y
end
def m
#z = nil if #x == 3
#x = 5
#y = 6
end
end
a1 = A.new(1,2)
#=> #<A:0x000057d1fd2d18e8 #x=1, #y=2>
a1.m
a1 #=> #<A:0x000057d1fd2d18e8 #x=5, #y=6>
a2 = A.new(3,4)
#=> #<A:0x000057d1fd46b460 #x=3, #y=4>
a2.m
a2
#=> #<A:0x000057d1fd46b460 #x=5, #y=6, #z=nil>
a1.instance_variables.all? { |e|
a1.instance_variable_get(e) == a2.instance_variable_get(e) } &&
a2.instance_variables.all? { |e|
a1.instance_variable_get(e) == a2.instance_variable_get(e) }
#=> true && true => true
We obtain this incorrect result because:
class A
end
A.new.instance_variable_get(:#z)
#=> nil
We therefore must confirm that if one instance has an instance variable named e, so does the other instance, and that each pair of instance variables with the same name are equal. One way to do that is as follows:
(a1.instance_variables.sort == a2.instance_variables.sort) &&
a1.instance_variables.all? { |e|
a1.instance_variable_get(e) == a2.instance_variable_get(e) }
#=> false && true => false
See Enumerable#all?, Object#instance_variables and Object#instance_variable_get.

How do I fix a problem to call a function in Ruby?

I'm trying to use some ruby code that I've found in Github. I've downloaded the code and did the necessary imports the "requires" and tried to run it as it is described in the readme file on github repository. The code is the following:
In the file pcset_test.rb the code is the following:
require './pcset.rb'
require 'test/unit'
#
# When possible, test cases are adapted from
# Introduction to Post-Tonal Theory by Joseph N. Straus,
# unless obvious or otherwise noted.
#
class PCSetTest < Test::Unit::TestCase
def test_init
#assert_raise(ArgumentError) {PCSet.new []}
assert_raise(ArgumentError) {PCSet.new [1, 2, 3, 'string']}
assert_raise(ArgumentError) {PCSet.new "string"}
assert_raise(ArgumentError) {PCSet.new [1, 2, 3.6, 4]}
assert_equal([0, 1, 2, 9], PCSet.new([0, 1, 2, 33, 13]).pitches)
assert_equal([3, 2, 1, 11, 10, 0], PCSet.new_from_string('321bac').pitches)
assert_equal([0,2,4,5,7,11,9], PCSet.new([12,2,4,5,7,11,9]).pitches)
assert_nothing_raised() {PCSet.new []}
end
def test_inversion
end
def test_transposition
end
def test_multiplication
end
#
# set normal prime forte #
# 0,2,4,7,8,11 7,8,11,0,2,4 0,1,4,5,7,9 6-31
# 0,1,2,4,5,7,11 11,0,1,2,4,5,7 0,1,2,3,5,6,8 7-Z36
# 0,1,3,5,6,7,9,10,11 5,6,7,9,10,11,0,1,3 0,1,2,3,4,6,7,8,10 9-8
#
def test_normal_form
testPC = PCSet.new [0,4,8,9,11]
assert_kind_of(PCSet, testPC.normal_form)
assert_equal([8,9,11,0,4], testPC.normal_form.pitches)
assert_equal([10,1,4,6], PCSet.new([1,6,4,10]).normal_form.pitches)
assert_equal([2,4,8,10], PCSet.new([10,8,4,2]).normal_form.pitches)
assert_equal([7,8,11,0,2,4], PCSet.new([0,2,4,7,8,11]).normal_form.pitches)
assert_equal([11,0,1,2,4,5,7], PCSet.new([0,1,2,4,5,7,11]).normal_form.pitches)
assert_equal([5,6,7,9,10,11,0,1,3], PCSet.new([0,1,3,5,6,7,9,10,11]).normal_form.pitches)
end
def test_prime_form
assert_equal([0,1,2,6], PCSet.new([5,6,1,7]).prime.pitches)
assert_equal([0,1,4], PCSet.new([2,5,6]).prime.pitches)
assert_equal([0,1,4,5,7,9], PCSet.new([0,2,4,7,8,11]).prime.pitches)
assert_equal([0,1,2,3,5,6,8], PCSet.new([0,1,2,4,5,7,11]).prime.pitches)
assert_equal([0,1,2,3,4,6,7,8,10], PCSet.new([0,1,3,5,6,7,9,10,11]).prime.pitches)
end
def test_set_class
testPcs = PCSet.new([2,5,6])
testPrime = testPcs.prime
assert_equal([
[2,5,6], [3,6,7], [4,7,8], [5,8,9], [6,9,10], [7,10,11],
[8,11,0],[9,0,1], [10,1,2],[11,2,3],[0,3,4], [1,4,5],
[6,7,10],[7,8,11],[8,9,0], [9,10,1],[10,11,2],[11,0,3],
[0,1,4], [1,2,5], [2,3,6], [3,4,7], [4,5,8], [5,6,9]
].sort, PCSet.new([2,5,6]).set_class.map{|x| x.pitches})
assert_equal(testPcs.set_class.map{|x| x.pitches}, testPrime.set_class.map{|x| x.pitches})
end
def test_interval_vector
assert_equal([2,1,2,1,0,0], PCSet.new([0,1,3,4]).interval_vector)
assert_equal([2,5,4,3,6,1], PCSet.new([0,1,3,5,6,8,10]).interval_vector)
assert_equal([0,6,0,6,0,3], PCSet.new([0,2,4,6,8,10]).interval_vector)
end
def test_complement
assert_equal([6,7,8,9,10,11], PCSet.new([0,1,2,3,4,5]).complement.pitches)
assert_equal([3,4,5], PCSet.new([0,1,2], 6).complement.pitches)
end
#
# Test values from (Morris 1991), pages 105-111
# Citation:
# Morris. Class Notes for Atonal Music Theory
# Lebanon, NH. Frog Peak Music, 1991.
#
def test_invariance_vector
assert_equal([1,0,0,0,5,6,5,5],PCSet.new([0,2,5]).invariance_vector)
assert_equal([2,2,2,2,6,6,6,6],PCSet.new([0,1,6,7]).invariance_vector)
assert_equal([6,6,6,6,6,6,6,6],PCSet.new([0,2,4,6,8,10]).invariance_vector)
assert_equal([1,0,0,0,0,0,0,0],PCSet.new([0,1,2,3,4,5,8]).invariance_vector)
assert_equal([1,0,0,1,0,0,0,0],PCSet.new([0,1,2,3,5,6,8]).invariance_vector)
assert_equal([12,12,12,12,0,0,0,0],PCSet.new([0,1,2,3,4,5,6,7,8,9,10,11]).invariance_vector)
end
#
# Test values from (Huron 1994). Huron rounds, thus the 0.01 margin of error.
# Citation:
# Huron. Interval-Class Content in Equally Tempered Pitch-Class Sets:
# Common Scales Exhibit Optimum Tonal Consonance.
# Music Perception (1994) vol. 11 (3) pp. 289-305
#
def test_huron
h1 = PCSet.new([0,1,2,3,4,5,6,7,8,9,10,11]).huron
assert_in_delta(-0.2, h1[0], 0.01)
assert_in_delta(0.21, h1[1], 0.01)
h2 = PCSet.new([0,2,4,5,7,9,11]).huron
assert_in_delta(4.76, h2[0], 0.01)
assert_in_delta(0.62, h2[1], 0.01)
end
def test_coherence
end
end
And in the file pcset.rb the folloing code:
#
# => PCSet Class for Ruby
# => Beau Sievers
# => Hanover, Fall 2008.
#
#
# TODO: Make this a module to avoid namespace collisions.
# Lilypond and MusicXML output
#
include Math
def choose(n, k)
return [[]] if n.nil? || n.empty? && k == 0
return [] if n.nil? || n.empty? && k > 0
return [[]] if n.size > 0 && k == 0
c2 = n.clone
c2.pop
new_element = n.clone.pop
choose(c2, k) + append_all(choose(c2, k-1), new_element)
end
def append_all(lists, element)
lists.map { |l| l << element }
end
def array_to_binary(array)
array.inject(0) {|sum, n| sum + 2**n}
end
# the following method is horrifically inelegant
# but avoids monkey-patching.
# TODO: do this right, incl. error checking
def pearsons(x, y)
if !x.is_a?(Array) || !y.is_a?(Array) then raise StandardError, "x and y must be arrays", caller end
if x.size != y.size then raise StandardError, "x and y must be same size", caller end
sum_x = x.inject(0) {|sum, n| sum + n}
sum_y = y.inject(0) {|sum, n| sum + n}
sum_square_x = x.inject(0) {|sum, n| sum + n * n}
sum_square_y = y.inject(0) {|sum, n| sum + n * n}
xy = []
x.zip(y) {|a, b| xy.push(a * b)}
sum_xy = xy.inject(0) {|sum, n| sum + n}
num = sum_xy - ((sum_x * sum_y)/x.size)
den = Math.sqrt((sum_square_x - ((sum_x*sum_x)/x.size)) * (sum_square_y - ((sum_y*sum_y)/x.size)))
(num/den)
end
class PCSet
include Comparable
attr_reader :pitches, :base, :input
def initialize(pcarray, base = 12)
if pcarray.instance_of?(Array) && pcarray.all?{|pc| pc.instance_of?(Fixnum)}
#base, #input = base, pcarray
#pitches = pcarray.map{ |x| x % #base }.uniq
else
raise ArgumentError, "Improperly formatted PC array", caller
end
end
def PCSet.new_from_string(pcstring, base = 12)
if base > 36 then raise StandardError, "Use PCSet.new to create pcsets with a base larger than 36", caller end
pcarray = []
pcstring.downcase.split(//).each do |c|
if c <= 'z' and c >= '0' then pcarray.push(c.to_i(36)) end
end
PCSet.new pcarray, base
end
def <=>(pcs)
#pitches <=> pcs.pitches
end
def [](index)
#pitches[index]
end
# Intersection
def &(other)
PCSet.new #pitches & other.pitches
end
# Union
def |(other)
PCSet.new #pitches | other.pitches
end
def inspect
#pitches.inspect
end
def length
#pitches.length
end
def invert(axis = 0)
PCSet.new #pitches.map {|x| (axis-x) % #base}
end
def invert!(axis = 0)
#pitches.map! {|x| (axis-x) % #base}
end
def transpose(interval)
PCSet.new #pitches.map {|x| (x + interval) % #base}
end
def transpose!(interval)
#pitches.map! {|x| (x + interval) % #base}
end
def multiply(m = 5)
PCSet.new #pitches.map {|x| (x * m) % #base}
end
def multiply!(m = 5)
#pitches.map! {|x| (x * m) % #base}
end
def zero
transpose(-1 * #pitches[0])
end
def zero!
transpose!(-1 * #pitches[0])
end
def transpositions
(0..(#base-1)).to_a.map{|x| #pitches.map {|y| (y + x) % #base}}.sort.map {|x| PCSet.new x}
end
def transpositions_and_inversions(axis = 0)
transpositions + invert(axis).transpositions
end
#
# Normal form after Straus. Morris and AthenaCL do this differently.
#
def normal_form
tempar = #pitches.sort
arar = [] # [[1,4,7,8,10],[4,7,8,10,1], etc.] get each cyclic variation
tempar.each {arar.push PCSet.new(tempar.unshift(tempar.pop))}
most_left_compact(arar)
end
def normal_form!
#pitches = normal_form.pitches
end
def is_normal_form?
self.pitches == self.normal_form.pitches
end
def set_class
transpositions_and_inversions.map{|pcs| pcs.normal_form}.sort
end
def prime
most_left_compact([normal_form.zero, invert.normal_form.zero])
end
def prime!
self.pitches = self.prime.pitches
end
def is_prime?
self.pitches == self.prime.pitches
end
def complement
new_pitches = []
#base.times do |p|
if !#pitches.include? p then
new_pitches.push p
end
end
PCSet.new new_pitches
end
def full_interval_vector
pairs = choose(#pitches, 2) # choose every pc pair
intervals = pairs.map {|x| (x[1] - x[0]) % #base} # calculate every interval
i_vector = Array.new(#base-1).fill(0)
intervals.each {|x| i_vector[x-1] += 1} # count the intervals
i_vector
end
def interval_vector
i_vector = full_interval_vector
(0..((#base-1)/2)-1).each {|x| i_vector[x] += i_vector.pop}
i_vector
end
#
# Morris's invariance vector
#
def invariance_vector(m = 5)
t = transpositions.map!{|pcs| self & pcs}
ti = invert.transpositions.map!{|pcs| self & pcs}
tm = multiply(m).transpositions.map!{|pcs| self & pcs}
tmi = invert.multiply(m).transpositions.map!{|pcs| self & pcs}
tc = complement.transpositions.map!{|pcs| self & pcs}
tic = complement.invert.transpositions.map!{|pcs| self & pcs}
tmc = complement.multiply(m).transpositions.map!{|pcs| self & pcs}
tmic = complement.invert.multiply(m).transpositions.map!{|pcs| self & pcs}
[t, ti, tm, tmi, tc, tic, tmc, tmic].map{|x| x.reject{|pcs| pcs.pitches != #pitches}.length}
end
# Huron's aggregate dyadic consonance measure.
# Huron. Interval-Class Content in Equally Tempered Pitch-Class Sets:
# Common Scales Exhibit Optimum Tonal Consonance.
# Music Perception (1994) vol. 11 (3) pp. 289-305
def huron
if #base != 12 then raise StandardError, "PCSet.huron only makes sense for mod 12 pcsets", caller end
# m2/M7 M2/m7 m3/M6 M3/m6 P4/P5 A4/d5
huron_table = [-1.428, -0.582, 0.594, 0.386, 1.240, -0.453]
interval_consonance = []
interval_vector.zip(huron_table) {|x, y| interval_consonance.push(x * y) }
aggregate_dyadic_consonance = interval_consonance.inject {|sum, n| sum + n}
[aggregate_dyadic_consonance, pearsons(interval_vector, huron_table)]
end
#
# Balzano's vector of relations. Citation for all Balzano methods:
#
# Balzano. "The Pitch Set as a Level of Description for Studying Musical
# Pitch Perception" in Music, Mind, and Brain ed. Clynes. Plenum Press. 1982.
#
def vector_of_relations
(0..length-1).to_a.map do |i|
(0..length-1).to_a.map do |j|
(#pitches[(i + j) % length] - #pitches[i]) % #base
end
end
end
#
# Checks if the set satisfies Balzano's uniqueness.
#
def is_unique?
vector_of_relations.uniq.size == vector_of_relations.size
end
#
# Checks if the set satisfies Balzano's scalestep-semitone coherence.
# For all s[i] and s[i1]:
# j < k => v[i][j] < v[i1][k]
# Where j and k are scalestep-counting indices.
# And unless v[i][j] == 6 (a tritone), in which case the strict inequality is relaxed.
#
def is_coherent?
v = vector_of_relations
truth_array = []
all_pair_indices = choose((0..length-1).to_a, 2)
all_pair_indices.each do |i, i1|
all_pair_indices.each do |j, k|
if v[i][j] == 6
truth_array.push(v[i][j] <= v[i1][k])
else
truth_array.push(v[i][j] < v[i1][k])
end
if v[i1][j] == 6
truth_array.push(v[i1][j] <= v[i][k])
else
truth_array.push(v[i1][j] < v[i][k])
end
end
end
!truth_array.include?(false)
end
#
# Strict Balzano coherence, no inequality relaxation for tritones.
#
def is_strictly_coherent?
v = vector_of_relations
truth_array = []
all_pair_indices = choose((0..length-1).to_a, 2)
all_pair_indices.each do |i, i1|
all_pair_indices.each do |j, k|
truth_array.push(v[i][j] < v[i1][k])
truth_array.push(v[i1][j] < v[i][k])
end
end
!truth_array.include?(false)
end
def notes(middle_c = 0)
noteArray = ['C','C#','D','D#','E','F','F#','G','G#','A','A#','B']
if #base != 12 then raise StandardError, "PCSet.notes only makes sense for mod 12 pcsets", caller end
out_string = String.new
transpose(-middle_c).pitches.each do |p|
out_string += noteArray[p] + ", "
end
out_string.chop.chop
end
def info
print "modulo: #{#base}\n"
print "raw input: #{#input.inspect}\n"
print "pitch set: #{#pitches.inspect}\n"
print "notes: #{notes}\n"
print "normal: #{normal_form.inspect}\n"
print "prime: #{prime.inspect}\n"
print "interval vector: #{interval_vector.inspect}\n"
print "invariance vector: #{invariance_vector.inspect}\n"
print "huron ADC: #{huron[0]} pearsons: #{huron[1]}\n"
print "balzano coherence: "
if is_strictly_coherent?
print "strictly coherent\n"
elsif is_coherent?
print "coherent\n"
else
print "false\n"
end
end
# def lilypond
#
# end
#
# def musicXML
#
# end
###############################################################################
private
#
# Convert every pitch array to a binary representation, e.g.:
# [0,2,4,8,10] -> 010100010101
# 2^n: BA9876543210
# The smallest binary number is the most left-compact.
#
def most_left_compact(pcset_array)
if !pcset_array.all? {|pcs| pcs.length == pcset_array[0].length}
raise ArgumentError, "PCSet.most_left_compact: All PCSets must be of same cardinality", caller
end
zeroed_pitch_arrays = pcset_array.map {|pcs| pcs.zero.pitches}
binaries = zeroed_pitch_arrays.map {|array| array_to_binary(array)}
winners = []
binaries.each_with_index do |num, i|
if num == binaries.min then winners.push(pcset_array[i]) end
end
winners.sort[0]
end
end
I'm calling them as follows:
> my_pcset = PCSet.new([0,2,4,6,8,10])
> my_pcset2 = PCSet.new([1,5,9])
It shoud return:
> my_pcset = PCSet.new([0,2,4,6,8,10])
=> [0, 2, 4, 6, 8, 10]
> my_pcset2 = PCSet.new([1,5,9])
=> [1, 5, 9]
But is returning nothing.
The code is available on github
Thanks

Try this in terminal: irb -r ./path_to_directory/pcset.rb and then initialize the objects.

I think the documentation for the repo is bad as it does not explain how you should be running this.
The result of
my_pcset = PCSet.new([0,2,4,6,8,10])
should set my_pcset to an instance of a PCSet not an array, so these lines from the README file are confusing at best.
3. How to use it
Make new PCSets:
my_pcset = PCSet.new([0,2,4,6,8,10])
=> [0, 2, 4, 6, 8, 10]
my_pcset2 = PCSet.new([1,5,9])
=> [1, 5, 9]
Looking at the code, I see inspect has been delegated to #pitches
def inspect
#pitches.inspect
end
I think if you inspect my_pcset you will get the expected result.
my_pcset = PCSet.new([0,2,4,6,8,10])
p my_pcset # will print [0, 2, 4, 6, 8, 10]
or `my_pcset.inspect` will return what you are expecting.

Turning a method into an enumerable method

I rewrote the map method:
def my_map(input, &block)
mod_input = []
x = -1
while x < input.length - 1
x = x + 1
if block == nil
return input
break
end
mod_input.push(block.call(input[x]))
end
return mod_input
end
I need to call this code as I would call map or reverse. Does anyone know the syntax for that?

Are you asking how you put a method into a module? That's trivial:
module Enumerable
def my_map(&block)
mod_input = []
x = -1
while x < length - 1
x = x + 1
if block == nil
return self
break
end
mod_input.push(block.call(self[x]))
end
return mod_input
end
end
[1, 2, 3, 4, 5].my_map(&2.method(:*))
# => [2, 4, 6, 8, 10]
Or are you asking how to make your method an Enumerable method? That's more involved: your method currently uses many methods that are not part of the Enumerable API. So, even if you make it a member of the Enumerable module, it won't be an Enumerable method. Enumerable methods can only use each or other Enumerable methods. You use length and [] both of which are not part of the Enumerable interface, for example, Set doesn't respond to [].
This would be a possible implementation, using the Enumerable#inject method:
module Enumerable
def my_map
return enum_for(__method__) unless block_given?
inject([]) {|res, el| res << yield(el) }
end
end
[1, 2, 3, 4, 5].my_map(&2.method(:*))
# => [2, 4, 6, 8, 10]
A less elegant implementation using each
module Enumerable
def my_map
return enum_for(__method__) unless block_given?
[].tap {|res| each {|el| res << yield(el) }}
end
end
[1, 2, 3, 4, 5].my_map(&2.method(:*))
# => [2, 4, 6, 8, 10]
Note that apart from being simply wrong, your code is very un-idiomatic. There is also dead code in there.
the break is dead code: the method returns in the line just before it, therefore the break will never be executed. You can just get rid of it.
def my_map(&block)
mod_input = []
x = -1
while x < length - 1
x = x + 1
if block == nil
return self
end
mod_input.push(block.call(self[x]))
end
return mod_input
end
Now that we have gotten rid of the break, we can convert the conditional into a guard-style statement modifier conditional.
def my_map(&block)
mod_input = []
x = -1
while x < length - 1
x = x + 1
return self if block == nil
mod_input.push(block.call(self[x]))
end
return mod_input
end
It also doesn't make sense that it is in the middle of the loop. It should be at the beginning of the method.
def my_map(&block)
return self if block == nil
mod_input = []
x = -1
while x < length - 1
x = x + 1
mod_input.push(block.call(self[x]))
end
return mod_input
end
Instead of comparing an object against nil, you should just ask it whether it is nil?: block.nil?
def my_map(&block)
return self if block.nil?
mod_input = []
x = -1
while x < length - 1
x = x + 1
mod_input.push(block.call(self[x]))
end
return mod_input
end
Ruby is an expression-oriented language, the value of the last expression that is evaluated in a method body is the return value of that method body, there is no need for an explicit return.
def my_map(&block)
return self if block.nil?
mod_input = []
x = -1
while x < length - 1
x = x + 1
mod_input.push(block.call(self[x]))
end
mod_input
end
x = x + 1 is more idiomatically written x += 1.
def my_map(&block)
return self if block.nil?
mod_input = []
x = -1
while x < length - 1
x += 1
mod_input.push(block.call(self[x]))
end
mod_input
end
Instead of Array#push with a single argument it is more idiomatic to use Array#<<.
def my_map(&block)
return self if block.nil?
mod_input = []
x = -1
while x < length - 1
x += 1
mod_input << block.call(self[x])
end
mod_input
end
Instead of Proc#call, you can use the .() syntactic sugar.
def my_map(&block)
return self if block.nil?
mod_input = []
x = -1
while x < length - 1
x += 1
mod_input << block.(self[x])
end
mod_input
end
If you don't want to store, pass on or otherwise manipulate the block as an object, there is no need to capture it as a Proc. Just use block_given? and yield instead.
def my_map
return self unless block_given?
mod_input = []
x = -1
while x < length - 1
x += 1
mod_input << yield(self[x])
end
mod_input
end
This one is opinionated. You could move incrementing the counter into the condition.
def my_map
return self unless block_given?
mod_input = []
x = -1
while (x += 1) < length
mod_input << yield(self[x])
end
mod_input
end
And then use the statement modifier form.
def my_map
return self unless block_given?
mod_input = []
x = -1
mod_input << yield(self[x]) while (x += 1) < length
mod_input
end
Also, your variable names could use some improvements. For example, what does mod_input even mean? All I can see is that it is what you output, so why does it even have "input" in its name? And what is x?
def my_map
return self unless block_given?
result = []
index = -1
result << yield(self[index]) while (index += 1) < length
result
end
This whole sequence of initializing a variable, then mutating the object assigned to that variable and lastly returning the object can be simplified by using the K Combinator, which is available in Ruby as Object#tap.
def my_map
return self unless block_given?
[].tap {|result|
index = -1
result << yield(self[index]) while (index += 1) < length
}
end
The entire while loop is useless. It's just re-implementing Array#each, which is a) unnecessary because Array#each already exists, and b) means that your my_map method will only work with Arrays but not other Enumerables (for example Set or Enumerator). So, let's just use each instead.
def my_map
return self unless block_given?
[].tap {|result|
each {|element|
result << yield(element)
}
}
end
Now it starts to look like Ruby code! What you had before was more like BASIC written in Ruby syntax.
This pattern of first creating a result object, then modifying that result object based on each element of a collection and in the end returning the result is very common, and it even has a fancy mathematical name: Catamorphism, although in the programming world, we usually call it fold or reduce. In Ruby, it is called Enumerable#inject.
def my_map
return self unless block_given?
inject([]) {|result, element|
result << yield(element)
}
end
That return self is strange. map is supposed to return a new object! You don't return a new object, you return the same object. Let's fix that.
def my_map
return dup unless block_given?
inject([]) {|result, element|
result << yield(element)
}
end
And actually, map is also supposed to return an Array, but you return whatever it is that you called map on.
def my_map
return to_a unless block_given?
inject([]) {|result, element|
result << yield(element)
}
end
But really, if you look at the documentation of Enumerable#map, you will find that it returns an Enumerator and not an Array when called without a block.
def my_map
return enum_for(:my_map) unless block_given?
inject([]) {|result, element|
result << yield(element)
}
end
And lastly, we can get rid of the hardcoded method name using the Kernel#__method__ method.
def my_map
return enum_for(__method__) unless block_given?
inject([]) {|result, element|
result << yield(element)
}
end
Now, that looks a lot better!

class Array
def my_map(&block)
# your code, replacing `input` with `self`
end
end
The code itself is not really idiomatic Ruby - while is very rarely used for iteration over collections, and if you don't need to pass a block somewhere else, it is generally cleaner to use block_given? instead of block.nil? (let alone block == nil), and yield input[x] instead of block.call(input[x]).

How to yield 2 blocks in 1 method

How can I yield two diferent blocks in the same method
the example code:
def by_two(n,a)
yield n
yield a
end
proc1 = proc {|x| p x * 2}
proc2 = proc {|x| x + 100}
by_two(10, 300, &proc1, &proc2)
the error is such -
main.rb:7: syntax error, unexpected ',', expecting ')'
by_two(10, 300, &proc1, &proc2)
Any suggestions where and what is wrong? Thanks

Blocks are a lightweight way of passing a single anonymous procedure to a method. So, by definition, there cannot be two blocks passed to a method. It's not just semantically impossible, it isn't even possible syntactically.
Ruby does support first-class procedures in the form of Procs, however, and since those are just objects like any other object, you can pass as many of them as you want:
def by_two(n, a, proc1, proc2)
proc1.(n)
proc2.(a)
end
proc1 = proc {|x| p x * 2}
proc2 = proc {|x| x + 100}
by_two(10, 300, proc1, proc2)
# 20
# => 400
Since the introduction of lambda literals in Ruby 1.9, Procs are almost as syntactically lightweight as blocks, so there is not a big difference anymore:
by_two(10, 300, -> x { p x * 2 }, -> x { x + 100 })
# 20
# => 400

You cannot yield two blocks in a method.
But you can take two procs.
def by_two(n, a, pr1, pr2)
pr1.call(n)
pr2.call(a)
end
by_two(10, 300, proc1, proc2)

The answer to your question is: You cannot do it if you insist on blocks! Ruby does not support multiple blocks per method. A way to go around this is to pass two procs as variables like this:
def by_two(n,a, proc1=nil, proc2=nil)
if proc1 || proc2
proc1.yield n if proc1
puts proc2.yield a if proc2
else
puts "no procs"
end
end
proc1 = proc {|x| p x * 2}
proc2 = proc {|x| x + 100}
by_two(10, 300, proc1, proc2)
by_two(10, 300, proc1)
by_two(10, 300)
Output:
20
400
20
no procs
Another possibility is this:
NO_OP = proc {}
def by_two(n,a, proc1=NO_OP, proc2=NO_OP)
if proc1 == NO_OP && proc2 == NO_OP
puts "no procs"
else
proc1.yield n
proc2.yield a
end
end
proc1 = proc {|x| p x * 2}
proc2 = proc {|x| p x + 100}
by_two(10, 300, proc1, proc2)
by_two(10, 300, proc1)
by_two(10, 300)
It has the same output.

Ruby find max number w/o running method twice

I want to find the max number without running the function twice
def foo(num)
num * 10
end
def bar
x = 0
for i in 0..5
if foo(i) > x
x = foo(i) # I don't want to run foo a second time
end
end
end

How about
def bar
(1..5).map{|i| foo(i)}.max
end
This will traverse 1 to 5, and max a new enumerable with foo(i) instead of i, then return the max.

If you want the value of x:
define_method(:foo) { |x| x * 10 }
(1..5).max_by { |x| foo(x) }
#=> 5
If you want the value of f(x):
(1..5).map { |x| foo(x) }.max
#=> 50

You can save the result of the function as a variable, so you can use it later without calling the function again.
Applied to your code example, it would look like this:
#...
fooOfI = foo(i)
if fooOfI > x
x = fooOfI
end
#...

Store the result of the method in a local variable.
def bar
x = 0
for i in 0..5
foo_result = foo i
if foo_result > x
x = foo_result
end
end
end

I would do some change in your code :
def foo(num)
num * 10
end
def bar
x = 0
for i in 0..5
_,x = [foo(i),x].sort #or you can write as x = [foo(i),x].max
end
x
end
p bar
# >> 50

Elegant and simple
foo = -> x { x * 10 }
(1..5).map(&foo).max
# => 50
In one iteration (no so elegant but performs better)
def foo(num); num * 10; end;
(1..5).reduce(-1.0/0) { |a, e| f = foo(e); f > a ? f : a }
# => 50

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