Global Nerdy

# How about an array of the name of the first cosmonauts and astronauts,
# listed in the chronological order of the missions?
mission_leaders = ["Gagarin", "Shepard", "Grissom", "Titov", "Glenn", "Carpenter",
"Nikolayev", "Popovich"]
=> ["Gagarin", "Shepard", "Grissom", "Titov", "Glenn", "Carpenter", "Nikolayev",
"Popovich"]

# Yuri Gagarin was the first in space
mission_leaders.find_index{|leader| leader == "Gagarin"}
=> 0

# John Glenn was the fifth
mission_leaders.find_index{|leader| leader == "Glenn"}
=> 4

# And James Tiberius Kirk is not listed in the array
kirk_present = mission_leaders.find_index{|leader| leader == "Kirk"}
=> nil

require 'date'
=> true

# These are the names of the first manned spaceships and their launch dates
launch_dates = {"Kedr"              => Date.new(1961, 4, 12),
                "Freedom 7"         => Date.new(1961, 5, 5),
                "Liberty Bell 7"    => Date.new(1961, 7, 21),
                "Orel"              => Date.new(1961, 8, 6),
                "Friendship 7"      => Date.new(1962, 2, 20),
                "Aurora 7"          => Date.new(1962, 5, 24),
                "Sokol"             => Date.new(1962, 8, 11),
                "Berkut"            => Date.new(1962, 8, 12)}
=> {"Kedr"=>#<Date: 4874803/2,0,2299161>, "Freedom 7"=>#<Date: 4874849/2,0,2299161>,
"Liberty Bell 7"=>#<Date: 4875003/2,0,2299161>, "Orel"=>#<Date: 4875035/2,0,2299161>,
"Friendship 7"=>#<Date: 4875431/2,0,2299161>, "Aurora 7"=>#<Date: 4875617/2,0,2299161>,
"Sokol"=>#<Date: 4875775/2,0,2299161>, "Berkut"=>#<Date: 4875777/2,0,2299161>}

# Where in the list is John Glenn's ship, the Friendship 7?
launch_dates.find_index{|ship, date| ship == "Friendship 7"}
=> 4

# Where in the list is the first mission launched in August 1962?
launch_dates.find_index{|ship, date| date.year == 1962 && date.month == 8}
=> 6

# The same thing, expressed a little differently
launch_dates.find_index{|launch| launch[1].year == 1962 && launch[1].month == 8}
=> 6

# Once again, the mission leaders
mission_leaders = ["Gagarin", "Shepard", "Grissom", "Titov", "Glenn", "Carpenter",
"Nikolayev", "Popovich"]
=> ["Gagarin", "Shepard", "Grissom", "Titov", "Glenn", "Carpenter", "Nikolayev",
 "Popovich"]

# Yuri Gagarin is in the list
gagarin_in_list = mission_leaders.find_index {|leader| leader == "Gagarin"}
=> 0

# Captain James T. Kirk is not
kirk_in_list = mission_leaders.find_index {|leader| leader == "Kirk"}
=> nil

# gagarin_in_list is 0, which as a non-false and non-nil value evaluates as true.
# We can use it as both a membership test *and* as his location in the list.
p "Gagarin's there. He's number #{gagarin_in_list + 1} in the list." if gagarin_in_list
"Gagarin's there. He's number 1 in the list."
=> "Gagarin's there. He's number 1 in the list."

# kirk_in_list is nil, which is one of Ruby's two "false" values.
# Let's use it with the "something OR something else" idiom that
# many Ruby programmers like.
kirk_in_list || (p "You only *think* he wasn't there.")
"You only *think* he wasn't there."
=> "You only *think* he wasn't there."

# What the docs say (does not work yet!)
["Alice", "Bob", "Carol"].find_index("Bob")
=> 1

# What happens with the current version of Ruby 1.9
["Alice", "Bob", "Carol"].find_index("Bob")
ArgumentError: wrong number of arguments(1 for 0)
...