Related
I want to return an array of sums of multiples of 3 and 5 from 0 to n. And I want to return "invalid" when the input is a string, a float or < 0
def is_multiple_of_3_or_5(n)
if n.class == Integer && n > 0
n % 3 == 0 || n % 5 == 0 ? true : false
else
puts "invalid"
end
end
def sum_of_3_and_5_multiples(n)
if n.class == Integer
i = 0
array_of_multiples_of_3_and_5 = Array.new
while i < n
array_of_multiples_of_3_and_5 << i if is_multiple_of_3_or_5(i) == true
i += 1
end
array_of_multiples_of_3_and_5.inject(0, :+)
end
end
sum_of_3_and_5_multiples(-1)
To get the sums of multiples of 3 and 5 I got this but when I try with -1 that return me 0 instead "invalid", with"string"` that return me an error.
You havent' put any code in your sum_of_3_and_5_multiples method to handle what happens if is_multiple_of_3_or_5 is invalid (or to put it another way, a string). You also don't need to puts 'invalid', as this returns a value of null. Just 'invalid' will do:
def is_multiple_of_3_or_5(n)
if n.class == Integer && n > 0
n % 3 == 0 || n % 5 == 0 ? true : false
else
"invalid"
end
end
def sum_of_3_and_5_multiples(n)
if n.class == Integer
i = 0
array_of_multiples_of_3_and_5 = Array.new
while i < n
return "invalid" if is_multiple_of_3_or_5(i).is_a?(String)
array_of_multiples_of_3_and_5 << i if is_multiple_of_3_or_5(i) == true
i += 1
end
array_of_multiples_of_3_and_5.inject(0, :+)
end
end
sum_of_3_and_5_multiples(-1)
=> "invalid"
One could do that as follows.
def sum_of_3_and_5_multiples(n)
case n
when Float, String, -Float::INFINITY...0
return 'invalid'
end
((0..n).step(3).to_a + (0..n).step(5).to_a).uniq
end
sum_of_3_and_5_multiples(11.5)
#=> "invalid"
sum_of_3_and_5_multiples("11")
#=> "invalid"
sum_of_3_and_5_multiples(-340)
#=> "invalid"
sum_of_3_and_5_multiples(15)
#=> [0, 3, 6, 9, 12, 15, 5, 10]
sum_of_3_and_5_multiples(87)
#=> [0, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45,
# 48, 51, 54, 57, 60, 63, 66, 69, 72, 75, 78, 81, 84, 87,
# 5, 10, 20, 25, 35, 40, 50, 55, 65, 70, 80, 85]
Alternative verbose option, using a monkey patch to String class and a custom Class, stealing from Cary's answer (https://stackoverflow.com/a/59876202/5239030) but with a three dot Range for excluding the extreme value.
Patching the String class for using methods like this Numeric#integer? and Numeric#positive?. I'd suggest to use Kernel#raise in case of error.
module MyStringPatch
def integer?
false
end
def positive?
false
end
end
String.include MyStringPatch
Writing the custom class
class MyNumber
def initialize(n)
raise 'Invalid' unless n.integer? && n.positive?
#n = n
end
def sum_of_3_and_5_multiples
(((0...#n).step(3).to_a + (0...#n).step(5).to_a).uniq).sum
end
end
Finally using it
n = 32
my_number = MyNumber.new(n)
p my_number.sum_of_3_and_5_multiples
#=> 225
Or ...in initialize': Invalid (RuntimeError) in case of n = "32" or n = -32 or n = 32.0.
You can use something like:
return "invalid" unless n.is_a? Integer || n.positive?
Taking a look at: https://rubystyle.guide/ may help
I've found this ! that worked !
def is_multiple_of_3_or_5(n)
n % 3 == 0 || n % 5 == 0 || n == 0 ? true : false
end
def sum_of_3_and_5_multiples(n)
puts n.class
if n.class == Integer && n >= 0
i = 0
array_of_multiples_of_3_and_5 = Array.new
while i < n
array_of_multiples_of_3_and_5 << i if is_multiple_of_3_or_5(i) == true
i += 1
end
return array_of_multiples_of_3_and_5.inject(0, :+)
end
if n.class != Integer || n < 0
return "invalid"
end
end
thanks for your help that was helpful !
I want to select the first 10 elements of an array that match a certain condition without having to loop through the whole array. I know that find gets me the first element. So for example, the code below gives me the first prime that is larger than 100:
require 'prime'
puts Prime.find {|p| p > 100 } #=> 101
Is there a way to get the first 10 primes that are bigger then 100?
In Ruby 2.0+ you can write:
require 'prime'
Prime.lazy.select{|p| p > 100 }.take(10).to_a #=> [101, 103, 107, 109, 113, 127, 131, 137, 139, 149]
You can do it more manually like
def check_for_primes(start_number, desired_size)
result = []
suspect = start_number
while result.size < desired_size do
result << suspect if suspect.prime?
suspect += 1
end
result
end
check_for_primes 100, 10
#=> [101, 103, 107, 109, 113, 127, 131, 137, 139, 149]
with a simple ruby iteration.
Which works with all ruby versions.
instead of the (indisputably non ruby like) while loop, we can add #cary-swoveland 's variation, which has quite some ruby goodness in it.
check_enum_text(start_number, desired_size)
(start_number..1.0/0).each_with_object([]) do |n,arr|
if n.prime?
arr << n;
return arr if arr.size == desired_size
end
end
end
***********UPDATE***********
and some benchmarks for performance
require 'benchmark'
a_gazillion = 10000000000
Benchmark.bm do |x|
x.report("lazy_select") { Prime.lazy.select{|p| p > (a_gazillion / 1000) }.take(10).to_a }
x.report("prime_each") { arr = []; Prime.each{|p| arr << p if p > a_gazillion / 1000; break if arr.count == 10 } }
x.report("while_loop") { check_for_primes a_gazillion, 10 }
x.report("enum_text") { check_enum_text a_gazillion, 10 }
end
user system total real
lazy_select 75.360000 0.240000 75.600000 (84.259781)
prime_each 6.100000 0.040000 6.140000 ( 6.730646)
while_loop 0.620000 0.000000 0.620000 ( 0.655504)
enum_text 0.610000 0.000000 0.610000 ( 0.770726)
from what we see the two latest solutions are the ones that perform the best. From some extra benchmarking (by tweaking the desired_size) I can not conclude to which one is better
def bench(start, length)
Benchmark.bm do |x|
x.report("enum_text") { check_enum_text start, length }
x.report("while_loop") { check_for_primes start, length}
end
end
bench a_gazillion, 100
user system total real
enum_text 6.350000 0.000000 6.350000 ( 6.974557)
while_loop 6.530000 0.000000 6.530000 ( 7.330884)
bench a_gazillion, 500
user system total real
enum_text 31.880000 0.110000 31.990000 ( 36.723209)
while_loop 32.850000 0.060000 32.910000 ( 38.569744)
Performance is similar (actually #cary-swoveland's solution performs slightly better), so I will have to go with that solution since it is more ruby like!!
arr = []
Prime.each{|p| arr << p if p > 100; break if arr.count == 10 }
puts arr
Some of the answers have the disadvantage that they enumerate primes below the threshold multiple times. Here is one way to avoid that:
require 'prime'
def check_for_primes(start_number, desired_size)
return [] if desired_size.zero?
enum = Prime.each
[enum.find { |n| n >= start_number }] + enum.first(desired_size-1)
end
check_for_primes(100, 10)
#=> [101, 103, 107, 109, 113, 127, 131, 137, 139, 149]
Alternatively, this could be written:
def check_for_primes(start_number, desired_size)
return [] if desired_size.zero?
enum = Prime.each
(0..1.0/0).each_with_object([]) do |_,arr|
n = enum.next
if n >= start_number
arr << n
return arr if arr.size == desired_size
end
end
end
A simple iterative way:
require 'prime'
initial = 100
list = []
10.times do |x|
initial = Prime.find {|p| p > initial}
list << initial
end
puts list
You can use Prime.each(n) to have an upper limit:
Prime.each(1000).drop_while { |p| p <= 100 }.take(10)
# => [101, 103, 107, 109, 113, 127, 131, 137, 139, 149]
Alternatively, you can count have many primes are below 100, then take that amount + 10:
Prime.take(Prime.take_while { |p| p <= 100 }.count + 10)[-10..-1]
# => [101, 103, 107, 109, 113, 127, 131, 137, 139, 149]
Is there a built in way of printing a readable matrix in Ruby?
For example
require 'matrix'
m1 = Matrix[[1,2], [3,4]]
print m1
and have it show
=> 1 2
3 4
in the REPL instead of:
=> Matrix[[1,2][3,4]]
The Ruby Docs for matrix make it look like that's what should show happen, but that's not what I'm seeing. I know that it would be trivial to write a function to do this, but if there is a 'right' way I'd rather learn!
You could convert it to an array:
m1.to_a.each {|r| puts r.inspect}
=> [1, 2]
[3, 4]
EDIT:
Here is a "point free" version:
puts m1.to_a.map(&:inspect)
I couldn't get it to look like the documentation so I wrote a function for you that accomplishes the same task.
require 'matrix'
m1 = Matrix[[1,2],[3,4],[5,6]]
class Matrix
def to_readable
i = 0
self.each do |number|
print number.to_s + " "
i+= 1
if i == self.column_size
print "\n"
i = 0
end
end
end
end
m1.to_readable
=> 1 2
3 4
5 6
Disclaimer: I'm the lead developer for NMatrix.
It's trivial in NMatrix. Just do matrix.pretty_print.
The columns aren't cleanly aligned, but that'd be easy to fix and we'd love any contributions to that effect.
Incidentally, nice to see a fellow VT person on here. =)
You can use the each_slice method combined with the column_size method.
m1.each_slice(m1.column_size) {|r| p r }
=> [1,2]
[3,4]
Ok, I'm a total newbie in ruby programming. I'm just making my very first incursions, but it happens I got the same problem and made this quick'n'dirty approach.
Works with the standard Matrix library and will print columns formatted with same size.
class Matrix
def to_readable
column_counter = 0
columns_arrays = []
while column_counter < self.column_size
maximum_length = 0
self.column(column_counter).each do |column_element|# Get maximal size
length = column_element.to_s.size
if length > maximal_length
maximum_length = length
end
end # now we've got the maximum size
column_array = []
self.column(column_counter).each do |column_element| # Add needed spaces to equalize each column
element_string = column_element.to_s
element_size = element_string.size
space_needed = maximal_length - element_size +1
if space_needed > 0
space_needed.times {element_string.prepend " "}
if column_counter == 0
element_string.prepend "["
else
element_string.prepend ","
end
end
column_array << element_string
end
columns_arrays << column_array # Now columns contains equal size strings
column_counter += 1
end
row_counter = 0
while row_counter < self.row_size
columns_arrays.each do |column|
element = column[row_counter]
print element #Each column yield the correspondant row in order
end
print "]\n"
row_counter += 1
end
end
end
Any correction or upgrades welcome!
This is working for me
require 'matrix'
class Matrix
def print
matrix = self.to_a
field_size = matrix.flatten.collect{|i|i.to_s.size}.max
matrix.each do |row|
puts (row.collect{|i| ' ' * (field_size - i.to_s.size) + i.to_s}).join(' ')
end
end
end
m = Matrix[[1,23,3],[123,64.5, 2],[0,0,0]]
m.print
Here is my answer:
require 'matrix'
class Matrix
def to_pretty_s
s = ""
i = 0
while i < self.column_size
s += "\n" if i != 0
j = 0
while j < self.row_size
s += ' ' if j != 0
s += self.element(i, j).to_s
j += 1
end
i += 1
end
s
end
end
m = Matrix[[0, 3], [3, 4]]
puts m # same as 'puts m.to_s'
# Matrix[[0, 3], [3, 4]]
puts m.to_pretty_s
# 0 3
# 3 4
p m.to_pretty_s
# "0 3\n3 4"
You could use Matrix#to_pretty_s to get a pretty string for format.
There is no inbuilt Ruby way of doing this. However, I have created a Module which can be included into Matrix that includes a method readable. You can find this code here, but it is also in the following code block.
require 'matrix'
module ReadableArrays
def readable(factor: 1, method: :rjust)
repr = to_a.map { |row|
row.map(&:inspect)
}
column_widths = repr.transpose.map { |col|
col.map(&:size).max + factor
}
res = ""
repr.each { |row|
row.each_with_index { |el, j|
res += el.send method, column_widths[j]
}
res += "\n"
}
res.chomp
end
end
## example usage ##
class Matrix
include ReadableArrays
end
class Array
include ReadableArrays
end
arr = [[1, 20, 3], [20, 3, 19], [-32, 3, 5]]
mat = Matrix[*arr]
p arr
#=> [[1, 20, 3], [20, 3, 19], [-2, 3, 5]]
p mat
#=> Matrix[[1, 20, 3], [20, 3, 19], [-2, 3, 5]]
puts arr.readable
#=>
# 1 20 3
# 20 3 19
# -32 3 5
puts mat.readable
#=>
# 1 20 3
# 20 3 19
# -32 3 5
puts mat.readable(method: :ljust)
#=>
# 1 20 3
# 20 3 19
# -32 3 5
puts mat.readable(method: :center)
#=>
# 1 20 3
# 20 3 19
# -32 3 5
I had this problem just yet and haven't seen anyone posting it here, so I will put my solution if it helps someone. I know 2 for loops are not the best idea, but for smaller matrix it should be okay, and it prints beautifully and just how you want it, also without of use of require 'matrix' nor 'pp'
matrix = Array.new(numRows) { Array.new(numCols) { arrToTakeValuesFrom.sample } }
for i in 0..numRows-1 do
for j in 0..numCols-1 do
print " #{matrix[i][j]} "
end
puts ""
end
I am implementing my own RSA algorithm in ruby to learn more about the algorithm.
It is almost working, but when I decrypt it a few numbers don't decrypt but most do.
Why would this be?
For the given plaintext:
[ 42, 24, 424, 224, 421, 321]
The ciphertext is:
[1239,1263,1495,1349,208,1878]
Which when decrypted is:
[42,690,424,779,421,321]
This is the problem. Why is it happening?
These values are used to produce the keys (The method call is at the end of the program)
p = 51
q = 37
e = 223
n = 1887
phiN = 1800 (coprime with d)
d = 1687
class RSA
#edited to be concise, such as omitting initialize()
def encrypt(plainText)
index = 0
puts 'encrypt in is ', plainText
plainText.each do |i|
plainText[index] = ((i**(#e)) % #n )
index+=1
end
puts 'ciphertext is '
puts plainText
return plainText
end
def decrypt(cipherText)
puts 'decrypt in is ', cipherText
index = 0
cipherText.each do |i|
cipherText[index] = ((i**(#d)) % #n )
index+=1
end
puts 'plaintext is '
puts cipherText
return cipherText
end
def calcD()
#d=1
begin
s = (#d*#e)% #phiN;
#d+=1
end while not s==1
#d -= 1
#puts 'd is ', #d
end
end # class
message = RSA.new(51,37,223,[ 42, 24, 424, 224, 421, 321])
51 is not a prime.
Since that is one of the assumptions for the RSA algorithm, it should be no surprise that it fails to work.
Since your p is not a prime phi(n)!=(p-1)(q-1).
You could make it work by noticing that phi(51*37)=phi(3*17*37)=(3-1)(17-1)(37-1)=1152 and then calculating a working d=e^-1 (mod phi(n)) = 223^-1 (mod 1152) = 31, but I would recommend just using a prime p instead.
I have several records with a given attribute, and I want to find the standard deviation.
How do I do that?
module Enumerable
def sum
self.inject(0){|accum, i| accum + i }
end
def mean
self.sum/self.length.to_f
end
def sample_variance
m = self.mean
sum = self.inject(0){|accum, i| accum +(i-m)**2 }
sum/(self.length - 1).to_f
end
def standard_deviation
Math.sqrt(self.sample_variance)
end
end
Testing it:
a = [ 20, 23, 23, 24, 25, 22, 12, 21, 29 ]
a.standard_deviation
# => 4.594682917363407
01/17/2012:
fixing "sample_variance" thanks to Dave Sag
It appears that Angela may have been wanting an existing library. After playing with statsample, array-statisics, and a few others, I'd recommend the descriptive_statistics gem if you're trying to avoid reinventing the wheel.
gem install descriptive_statistics
$ irb
1.9.2 :001 > require 'descriptive_statistics'
=> true
1.9.2 :002 > samples = [1, 2, 2.2, 2.3, 4, 5]
=> [1, 2, 2.2, 2.3, 4, 5]
1.9.2p290 :003 > samples.sum
=> 16.5
1.9.2 :004 > samples.mean
=> 2.75
1.9.2 :005 > samples.variance
=> 1.7924999999999998
1.9.2 :006 > samples.standard_deviation
=> 1.3388427838995882
I can't speak to its statistical correctness, or your comfort with monkey-patching Enumerable; but it's easy to use and easy to contribute to.
The answer given above is elegant but has a slight error in it. Not being a stats head myself I sat up and read in detail a number of websites and found this one gave the most comprehensible explanation of how to derive a standard deviation. http://sonia.hubpages.com/hub/stddev
The error in the answer above is in the sample_variance method.
Here is my corrected version, along with a simple unit test that shows it works.
in ./lib/enumerable/standard_deviation.rb
#!usr/bin/ruby
module Enumerable
def sum
return self.inject(0){|accum, i| accum + i }
end
def mean
return self.sum / self.length.to_f
end
def sample_variance
m = self.mean
sum = self.inject(0){|accum, i| accum + (i - m) ** 2 }
return sum / (self.length - 1).to_f
end
def standard_deviation
return Math.sqrt(self.sample_variance)
end
end
in ./test using numbers derived from a simple spreadsheet.
#!usr/bin/ruby
require 'enumerable/standard_deviation'
class StandardDeviationTest < Test::Unit::TestCase
THE_NUMBERS = [1, 2, 2.2, 2.3, 4, 5]
def test_sum
expected = 16.5
result = THE_NUMBERS.sum
assert result == expected, "expected #{expected} but got #{result}"
end
def test_mean
expected = 2.75
result = THE_NUMBERS.mean
assert result == expected, "expected #{expected} but got #{result}"
end
def test_sample_variance
expected = 2.151
result = THE_NUMBERS.sample_variance
assert result == expected, "expected #{expected} but got #{result}"
end
def test_standard_deviation
expected = 1.4666287874
result = THE_NUMBERS.standard_deviation
assert result.round(10) == expected, "expected #{expected} but got #{result}"
end
end
I'm not a big fan of adding methods to Enumerable since there could be unwanted side effects. It also gives methods really specific to an array of numbers to any class inheriting from Enumerable, which doesn't make sense in most cases.
While this is fine for tests, scripts or small apps, it's risky for larger applications, so here's an alternative based on #tolitius' answer which was already perfect. This is more for reference than anything else:
module MyApp::Maths
def self.sum(a)
a.inject(0){ |accum, i| accum + i }
end
def self.mean(a)
sum(a) / a.length.to_f
end
def self.sample_variance(a)
m = mean(a)
sum = a.inject(0){ |accum, i| accum + (i - m) ** 2 }
sum / (a.length - 1).to_f
end
def self.standard_deviation(a)
Math.sqrt(sample_variance(a))
end
end
And then you use it as such:
2.0.0p353 > MyApp::Maths.standard_deviation([1,2,3,4,5])
=> 1.5811388300841898
2.0.0p353 :007 > a = [ 20, 23, 23, 24, 25, 22, 12, 21, 29 ]
=> [20, 23, 23, 24, 25, 22, 12, 21, 29]
2.0.0p353 :008 > MyApp::Maths.standard_deviation(a)
=> 4.594682917363407
2.0.0p353 :043 > MyApp::Maths.standard_deviation([1,2,2.2,2.3,4,5])
=> 1.466628787389638
The behavior is the same, but it avoids the overheads and risks of adding methods to Enumerable.
The presented computation are not very efficient because they require several (at least two, but often three because you usually want to present average in addition to std-dev) passes through the array.
I know Ruby is not the place to look for efficiency, but here is my implementation that computes average and standard deviation with a single pass over the list values:
module Enumerable
def avg_stddev
return nil unless count > 0
return [ first, 0 ] if count == 1
sx = sx2 = 0
each do |x|
sx2 += x**2
sx += x
end
[
sx.to_f / count,
Math.sqrt( # http://wijmo.com/docs/spreadjs/STDEV.html
(sx2 - sx**2.0/count)
/
(count - 1)
)
]
end
end
As a simple function, given a list of numbers:
def standard_deviation(list)
mean = list.inject(:+) / list.length.to_f
var_sum = list.map{|n| (n-mean)**2}.inject(:+).to_f
sample_variance = var_sum / (list.length - 1)
Math.sqrt(sample_variance)
end
If the records at hand are of type Integer or Rational, you may want to compute the variance using Rational instead of Float to avoid errors introduced by rounding.
For example:
def variance(list)
mean = list.reduce(:+)/list.length.to_r
sum_of_squared_differences = list.map { |i| (i - mean)**2 }.reduce(:+)
sum_of_squared_differences/list.length
end
(It would be prudent to add special-case handling for empty lists and other edge cases.)
Then the square root can be defined as:
def std_dev(list)
Math.sqrt(variance(list))
end
In case people are using postgres ... it provides aggregate functions for stddev_pop and stddev_samp - postgresql aggregate functions
stddev (equiv of stddev_samp) available since at least postgres 7.1, since 8.2 both samp and pop are provided.
Or how about:
class Stats
def initialize( a )
#avg = a.count > 0 ? a.sum / a.count.to_f : 0.0
#stdev = a.count > 0 ? ( a.reduce(0){ |sum, v| sum + (#avg - v) ** 2 } / a.count ) ** 0.5 : 0.0
end
end
You can place this as helper method and assess it everywhere.
def calc_standard_deviation(arr)
mean = arr.sum(0.0) / arr.size
sum = arr.sum(0.0) { |element| (element - mean) ** 2 }
variance = sum / (arr.size - 1)
standard_deviation = Math.sqrt(variance)
end