4. Arrays

single_level = [ "this", "that", "the", "other" ]

# Ruby directly supports nested arrays
double_level = [ "this", "that", [ "the", "other" ] ]
still_single_level = [ "this", "that", [ "the", "other" ] ].flatten

a = [ "quick", "brown", "fox" ]
a = %w(Why are you teasing me?)

lines = <<"END_OF_HERE_DOC".gsub(/^\s*(.+)/, '\1')
    The boy stood on the burning deck,
    It was as hot as glass.
END_OF_HERE_DOC

bigarray = IO.readlines("mydatafile").collect { |l| l.chomp }

name = "Gandalf"
banner = %Q(Speak, #{name}, and welcome!)

host_info  = `host #{his_host}`

%x(ps #{$$})

banner = 'Costs only $4.95'.split(' ')

rax = %w! ( ) < > { } [ ] !

def commify_series(arr)
    return '' if not arr
    case arr.size
        when 0 then ''
        when 1 then arr[0]
        when 2 then arr.join(' and ')
        else arr[0..-2].join(', ') + ', and ' + arr[-1]
    end
end

array = [ "red", "yellow", "green" ]

print "I have ", array, " marbles\n"
# -> I have redyellowgreen marbles

# But unlike Perl:
print "I have #{array} marbles\n"
# -> I have redyellowgreen marbles
# So, needs:
print "I have #{array.join(' ')} marbles\n"
# -> I have red yellow green marbles

#!/usr/bin/ruby
# communify_series - show proper comma insertion in list output

def commify_series(arr)
    return '' if not arr
    sepchar = arr.find { |p| p =~ /,/ } ? '; ' : ', '
    case arr.size
        when 0 then ''
        when 1 then arr[0]
        when 2 then arr.join(' and ')
        else arr[0..-2].join(sepchar) + sepchar + 'and ' + arr[-1]
    end
end

lists = [
    [ 'just one thing' ],
    %w(Mutt Jeff),
    %w(Peter Paul Mary),
    [ 'To our parents', 'Mother Theresa', 'God' ],
    [ 'pastrami', 'ham and cheese', 'peanut butter and jelly', 'tuna' ],
    [ 'recycle tired, old phrases', 'ponder big, happy thoughts' ],
    [ 'recycle tired, old phrases',
      'ponder big, happy thoughts',
      'sleep and dream peacefully' ],
]

for list in lists do
    puts "The list is: #{commify_series(list)}."
end

#   (note: AFAIK Ruby doesn't allow gory change of Array length)
# grow the array by assigning nil to past the end of array
ary[new_size-1] = nil
# shrink the array by slicing it down
ary.slice!(new_size..-1)
# init the array with given size
Array.new(number_of_elems)
# assign to an element past the original end enlarges the array
ary[index_new_last_elem] = value

def what_about_that_array(a)
    print "The array now has ", a.size, " elements.\n"
    # Index of last element is not really interesting in Ruby
    print "Element #3 is `#{a[3]}'.\n"
end
people = %w(Crosby Stills Nash Young)
what_about_that_array(people)

# OO style
bad_users.each { |user|
    complain(user)
}
# or, functional style
for user in bad_users
    complain(user)
end

for var in ENV.keys.sort
    puts "#{var}=#{ENV[var]}"
end

for user in all_users
    disk_space = get_usage(user)
    if (disk_space > MAX_QUOTA)
        complain(user)
    end
end

for l in IO.popen("who").readlines
    print l if l =~ /^gc/ 
end

# we can mimic the obfuscated Perl way
while fh.gets               # $_ is set to the line just read
    chomp                   # $_ has a trailing \n removed, if it had one
    split.each { |w|        # $_ is split on whitespace
                            # but $_ is not set to each chunk as in Perl
        print w.reverse
    }
end
# ...or use a cleaner way
for l in fh.readlines
    l.chomp.split.each { |w| print w.reverse }
end

# same drawback as in problem 1.4, we can't mutate a Numeric...
array.collect! { |v| v - 1 }

a = [ .5, 3 ]; b = [ 0, 1 ]
for ary in [ a, b ]
    ary.collect! { |v| v * 7 }
end
puts "#{a.join(' ')} #{b.join(' ')}"

# we can mutate Strings, cool; we need a trick for the scalar
for ary in [ [ scalar ], array, hash.values ]
    ary.each { |v| v.strip! }     # String#strip rules :)
end

# not relevant in Ruby since we have always references
for item in array
    # do somethingh with item
end

unique = list.uniq

# generate a list of users logged in, removing duplicates
users = `who`.collect { |l| l =~ /(\w+)/; $1 }.sort.uniq
puts("users logged in: #{commify_series(users)}")  # see 4.2 for commify_series

a - b
# [ 1, 1, 2, 2, 3, 3, 3, 4, 5 ] - [ 1, 2, 4 ]  ->  [3, 5]

union = a | b
intersection = a & b
difference = a - b

array1.concat(array2)
# if you will assign to another object, better use:
new_ary = array1 + array2

members = [ "Time", "Flies" ]
initiates =  [ "An", "Arrow" ]
members += initiates

members = [ "Time", "Flies" ]
initiates = [ "An", "Arrow" ]
members[2,0] = [ "Like", initiates ].flatten

members[0] = "Fruit"
members[3,2] = "A", "Banana"

reversed = ary.reverse

ary.reverse_each { |e|
    # do something with e
}

descending = ary.sort.reverse
descending = ary.sort { |a,b| b <=> a }

# remove n elements from front of ary (shift n)
front = ary.slice!(0, n)

# remove n elements from the end of ary (pop n)
end_ = ary.slice!(-n .. -1)

# let's extend the Array class, to make that useful
class Array
    def shift2()
        slice!(0 .. 1)     # more symetric with pop2...
    end
    def pop2()
        slice!(-2 .. -1)
    end
end

friends = %w(Peter Paul Mary Jim Tim)
this, that = friends.shift2

beverages = %w(Dew Jolt Cola Sprite Fresca)
pair = beverages.pop2

# use Enumerable#detect (or the synonym Enumerable#find)
highest_eng = employees.detect { |emp| emp.category == 'engineer' }

# use Enumerable#select (or the synonym Enumerable#find_all)
bigs = nums.select { |i| i > 1_000_000 }
pigs = users.keys.select { |k| users[k] > 1e7 }

matching = `who`.select { |u| u =~ /^gnat / }

engineers = employees.select { |e| e.position == 'Engineer' }

secondary_assistance = applicants.select { |a|
    a.income >= 26_000 && a.income < 30_000
}

# normally you would have an array of Numeric (Float or
# Fixnum or Bignum), so you would use:
sorted = unsorted.sort
# if you have strings representing Integers or Floats
# you may specify another sort method:
sorted = unsorted.sort { |a,b| a.to_f <=> b.to_f }

# let's use the list of my own PID's
`ps ux`.split("\n")[1..-1].
    select { |i| i =~ /^#{ENV['USER']}/ }.
    collect { |i| i.split[1] }.
    sort { |a,b| a.to_i <=> b.to_i }.each { |i| puts i }
puts "Select a process ID to kill:"
pid = gets.chomp
raise "Exiting ... \n" unless pid && pid =~ /^\d+$/
Process.kill('TERM', pid.to_i)
sleep 2
Process.kill('KILL', pid.to_i)

descending = unsorted.sort { |a,b| b.to_f <=> a.to_f }

ordered = unordered.sort { |a,b| compare(a,b) }

precomputed = unordered.collect { |e| [compute, e] }
ordered_precomputed = precomputed.sort { |a,b| a[0] <=> b[0] }
ordered = ordered_precomputed.collect { |e| e[1] }

ordered = unordered.collect { |e| [compute, e] }.
    sort { |a,b| a[0] <=> b[0] }.
    collect { |e| e[1] }

for employee in employees.sort { |a,b| a.name <=> b.name }
    print employee.name, " earns \$ ", employee.salary, "\n"
end

# Beware! `0' is true in Ruby.
# For chaining comparisons, you may use Numeric#nonzero?, which
# returns num if num is not zero, nil otherwise
sorted = employees.sort { |a,b| (a.name <=> b.name).nonzero? || b.age <=> a.age }

users = []
# getpwent is not wrapped in Ruby... let's fallback
IO.readlines('/etc/passwd').each { |u| users << u.split(':') }
users.sort! { |a,b| a[0] <=> b[0] }
for user in users
    puts user[0]
end

sorted = names.sort { |a,b| a[1, 1] <=> b[1, 1] }
sorted = strings.sort { |a,b| a.length <=> b.length }

# let's show only the compact version
ordered = strings.collect { |e| [e.length, e] }.
    sort { |a,b| a[0] <=> b[0] }.
    collect { |e| e[1] }

ordered = strings.collect { |e| [/\d+/.match(e)[0].to_i, e] }.
    sort { |a,b| a[0] <=> b[0] }.
    collect { |e| e[1] }

print `cat /etc/passwd`.collect { |e| [e, e.split(':').indexes(3,2,0)].flatten }.
    sort { |a,b| (a[1] <=> b[1]).nonzero? || (a[2] <=> b[2]).nonzero? || a[3] <=> b[3] }.
    collect { |e| e[0] }

circular.unshift(circular.pop)        # the last shall be first
circular.push(circular.shift)         # and vice versa

def grab_and_rotate(l)
    l.push(ret = l.shift)
    ret
end

processes = [1, 2, 3, 4, 5]
while (1)
    process = grab_and_rotate(processes)
    puts "Handling process #{process}"
    sleep 1
end

def fisher_yates_shuffle(a)
    (a.size-1).downto(1) { |i|
        j = rand(i+1)
        a[i], a[j] = a[j], a[i] if i != j
    }
end

def naive_shuffle(a)
    for i in 0...a.size
        j = rand(a.size)
        a[i], a[j] = a[j], a[i]
    end
end

#!/usr/bin/env ruby
# example 4-2 words
# words - gather lines, present in colums

# class to encapsulate the word formatting from the input
class WordFormatter
    def initialize(cols)
        @cols = cols
    end

    # helper to return the length of the longest word in the wordlist
    def maxlen(wordlist)
        max = 1
        for word in wordlist
            if word.length > max
                max = word.length
            end
        end
        max
    end

    # process the wordlist and print it formmated into columns
    def output(wordlist)
        collen = maxlen(wordlist) + 1
        columns = @cols / collen
        columns = 1 if columns == 0
        rows = (wordlist.length + columns - 1) / columns
        # now process each item, picking out proper piece for this position
        0.upto(rows * columns - 1) { |item|
            target = (item % columns) * rows + (item / columns)
            eol = ((item+1) % columns == 0)
            piece = wordlist[target] || ""
            piece = piece.ljust(collen) unless eol
            print piece
            puts if eol
        }
        # no need to finish it up, because eol is always true for the last element
    end
end

# get nr of chars that fit in window or console, see PLEAC 15.4
# not portable -- linux only (?)
def getWinCharWidth()
    buf = "\0" * 8
    $stdout.ioctl(0x5413, buf)
    ws_row, ws_col, ws_xpixel, ws_ypixel = buf.unpack("$4")
    ws_col || 80
rescue
    80
end

# main program
cols = getWinCharWidth()
formatter = WordFormatter.new(cols)
words = readlines()
words.collect! { |line|
    line.chomp
}
formatter.output(words)

# In ruby, Fixnum's are automatically converted to Bignum's when
# needed, so there is no need for an extra module
def factorial(n)
    s = 1
    while n > 0
        s *= n
        n -= 1
    end
    s
end

puts factorial(500)

#---------------------------------------------------------
# Example 4-3. tsc-permute
# tsc_permute: permute each word of input
def permute(items, perms)
    unless items.length > 0
        puts perms.join(" ")
    else
        for i in items
            newitems = items.dup
            newperms = perms.dup
            newperms.unshift(newitems.delete(i))
            permute(newitems, newperms)
        end
    end
end
# In ruby the main program must be after all definitions it is using
permute(ARGV, [])

#---------------------------------------------------------
# mjd_permute: permute each word of input

def factorial(n)
    s = 1
    while n > 0
        s *= n
        n -= 1
    end
    s
end

# we use a class with a class variable store the private cache
# for the results of the factorial function.
class Factorial
    @@fact = [ 1 ]
    def Factorial.compute(n)
        if @@fact[n]
            @@fact[n]
        else
            @@fact[n] = n * Factorial.compute(n - 1)
        end
    end
end

#---------------------------------------------------------
# Example 4-4- mjd-permute
# n2pat(n, len): produce the N-th pattern of length len

# We must use a lower case letter as parameter N, otherwise it is
# handled as constant Length is the length of the resulting
# array, not the index of the last element (length -1) like in
# the perl example.
def n2pat(n, length)
    pat = []
    i = 1
    while i <= length
        pat.push(n % i)
        n /= i
        i += 1
    end
    pat
end

# pat2perm(pat): turn pattern returned by n2pat() into
# permutation of integers.
def pat2perm(pat)
    source = (0 .. pat.length - 1).to_a
    perm = []
    perm.push(source.slice!(pat.pop)) while pat.length > 0
    perm
end

def n2perm(n, len)
    pat2perm(n2pat(n,len))
end

# In ruby the main program must be after all definitions
while gets
    data = split
    # the perl solution has used $#data, which is length-1
    num_permutations = Factorial.compute(data.length())
    0.upto(num_permutations - 1) do |i|
        # in ruby we can not use an array as selector for an array
        # but by exchanging the two arrays, we can use the collect method
        # which returns an array with the result of all block invocations
        permutation = n2perm(i, data.length).collect {
            |j| data[j]
        }
        puts permutation.join(" ")
    end
end