shinokada

a = [1, 2, 3, 4]
(0...arr.length - 1).map{|i| arr.dup.tap{ |a| a[i, 2] = a[i, 2].reverse } }
# => [[2, 1, 3, 4, 5], [1, 3, 2, 4, 5], [1, 2, 4, 3, 5], [1, 2, 3, 5, 4]]
a = [1, 2, 3]
# => [1, 2, 3]
(0...a.length - 1).map{|i| a.dup.tap{|a| a[i, 2] = a[i, 2].reverse}}
# => [[2, 1, 3], [1, 3, 2]]

shinokada

# read text from file, map to integer and sum all
File.new(file_name, 'r').each_line.map(&:strip).map(&:to_i).inject(:+)

shinokada

require 'matrix'

arr = [
  %w(J O I J O),
  %w(I J O J O),
  %w(I I J I J)
]

myarr1 = Array(arr)
# [["J", "O", "I", "J", "O"], ["I", "J", "O", "J", "O"], ["I", "I", "J", "I", "J"]]

shinokada

# http://stackoverflow.com/questions/23382474/is-there-any-way-to-create-2-x-2-array-matrix-from-a-larger-array-matrix
require 'matrix'

def find_in_matrix(arr,sub)
  sub_nrows = sub.size
  sub_ncols = sub.first.size
  rows      = Array(0..(arr.size - sub_nrows))
  cols      = Array(0..(arr.first.size - sub_ncols))
  arr_m     = Matrix[*arr]
  sub_m     = Matrix[*sub]

shinokada

[[0, 0, 3], [0, 1, 4], [1, 0, 5], [1, 1, 6]].select{ |i, j, k| p "#{ i } is #{ j } is #{ k }" }
# "0 is 0 is 3"
# "0 is 1 is 4"
# "1 is 0 is 5"
# "1 is 1 is 6"
# => [[0, 0, 3], [0, 1, 4], [1, 0, 5], [1, 1, 6]]

shinokada

# 1.
a = [1, 2, 3]
b = [1, 4, 3]

a.zip(b).map { |x, y| x == y } # [true, false, true]A

# 2.
a.zip(b).collect {|x,y| x==y }
# => [true, false, true]

shinokada

# find number of item which has at least 3 numbers are the same

arr1 = [1, 2, 3, 4]

arr2 = [[2, 2, 2, 4],[1, 4, 3, 4],[1, 2, 1, 4],[1, 2, 3, 1],[2, 1, 3, 4]]
n = 0
arr2.map{|e| e.zip(arr1).collect{| x, y| x==y}}.each do |e| 
  if e.count(true) >=3
    n += 1
  end

shinokada

  def readfile1(file_name)
    # read a file and returns string "17 10 16 3 7 "
    file = File.open(file_name)
    contents = file.read.gsub(/\r\n/, ' ')
  end

  def readfile2(file_nam)
    # same as above
    File.readlines(file_name).map(&:chomp).join(' ')
  end

shinokada

# Ruby: How to find and return a duplicate value in array?

ary = ["A", "B", "C", "B", "A"]

ary.group_by { |e| e }.select { |k, v| v.size > 1 }.map(&:first) # => ["A", "B"]

ary.sort.chunk { |e| e }.select { |e, count| count.size > 1 }.map(&:first)

ary.select { |e| ary.count(e) > 1 }.uniq # => ["A", "B"]

shinokada

# file content
#
# 4
# bar
# abracadabra
# bear
# bar
# baraxbara