Tips for golfing in Ruby

Question

What general tips can you give for golfing in Ruby?

I'm looking for ideas that can be applied to code golf problems in general that are specific to Ruby. (For example, "Remove comments" would not be an answer.)

Please post one tip per answer.

• Mark Thomas: Someone needs to write a language called Rub, which uses a single Unicode character for every Ruby token, kinda like Jelly and Pyth :)

Answer 1

• The numbers 100 to 126 can be written as ?d to ?~ in 1.8.
• On a similar note if you need a single-character string in 1.9 ?x is shorter than "x".
• If you need to print a string without appending a newline, $><<"string" is shorter than print"string".
• If you need to read multiple lines of input $<.map{|l|...} is shorter than while l=gets;...;end. Also you can use $<.read to read it all at once.
• If you're supposed to read from a file, $< and gets will read from a file instead of stdin if the filename is in ARGV. So the golfiest way to reimplement cat would be: $><<$<.read.

• Hiato: ?x yields the ascii code in general, so you can realistically get all the printables to digits in two characters. 1.9 is different, 'a'.ord yields the ascii number, but is four bytes longer than the decimal version.
• daniero: An even golfier way to implement cat is to leave the ruby file completely empty (0 bytes) and insist that it should be run from the command line with the -p flag.
• Not that Charles: or, from @daniero's own answer, puts *$<
• Simply Beautiful Art: So in 1.8, all I have to do is go ?~ and it will return 126?
• Simply Beautiful Art: You can go beyond 126 using thinks like ☺ or ♫, or if you are crazy enough: ?﷽.ord=65021

Answer 2

Use the splat operator to get the tail and head of an array:

head, *tail = [1,2,3]
head => 1
tail => [2,3]

This also works the other way:

*head, tail = [1,2,3]
head => [1,2]
tail => 3

Use the * method with a string on an array to join elements:

[1,2,3]*?,
=> "1,2,3"

Answer 3

• Use abort to terminate the program and print a string to STDERR - shorter than puts followed by exit
• If you read a line with gets, you can then use ~/$/ to find its length (this doesn't count a trailing newline if it exists)
• Use [] to check if a string contains another: 'foo'['f'] #=> 'f'
• Use tr instead of gsub for character-wise substitutions: '01011'.tr('01','AB') #=> 'ABABB'
• If you need to remove trailing newlines, use chop instead of chomp

• Mathieu CAROFF: Please explain how to use ~/$/
• Cyoce: @MathieuCAROFF every time you call gets, its result is stored in the $_ variable. /regex/ ~= string returns the index of the first match. Calling ~ on a regex is equivalent to /regex/ ~= $_. So it would be something like s=gets;l= ~/$/

Answer 4

End your end.

Try to remove end from your code.

Don't use def...end to define functions. Make a lambda with the new -> operator in Ruby 1.9. (The -> operator is a "stabby lambda", or "dash rocket".) This saves 5 characters per function.

# 28 characters
def c n
/(\d)1円/=~n.to_s
end
# 23 characters, saves 5
c=->n{/(\d)1円/=~n.to_s}

Method calls are c n or c(n). Lambda calls are c[n]. Changing each c n to c[n] costs 1 character, so if you can use c n more than 5 times, then keep the method.

All methods that take do...end blocks can take {...} blocks instead. This saves 3 to 5 characters. If the precedence of {...} is too high, then use parentheses to fix it.

# 48 characters
(?a..?m).zip (1..5).cycle do|a|puts a.join','end
# WRONG: passes block to cycle, not zip
(?a..?m).zip (1..5).cycle{|a|puts a.join','}
# 45 characters, saves 3
(?a..?m).zip((1..5).cycle){|a|puts a.join','}

Replace if...else...end with the ternary operator ?:. If a branch has two or more statements, wrap them in parentheses.

# 67 characters
if a<b
puts'statement 1'
puts'statement 2'else
puts'statement 3'end
# 62 characters, saves 5
a<b ?(puts'statement 1'
puts'statement 2'):(puts'statement 3')

You probably don't have while or until loops, but if you do, then write them in modifier form.

(a+=1
b-=1)while a<b

• Cyoce: Are the parentheses around puts'statement 3' necessary?

Answer 5

Addition to w0lf

When working with arrays, .compact can be replaced with -[nil] to save 2 chars.

Combined with above -> you can make it even shorter with -[p] to save another 2 chars.

Answer 6

Use the short predefined variables wherever possible, e.g. $* instead of ARGV. There's a good list of them here, along with a lot of other useful information.

Answer 7

Use operator methods instead of parentheses

Let's say you want to express a*(b+c). Because of precedence, a*b+c won't work (obviously). Ruby's cool way of having operators as methods comes to the rescue! You can use a.*b+c to make the precedence of * lower than that of +.

a*(b+c) # too long
a*b+c # wrong
a.*b+c # 1 byte saved!

This can also work with the ! and ~ operators (things like unary + or unary - don't work because their methods are -@ and +@, saving () but adding .@)

(~x).to_s # too long
~x.to_s # error
x.~.to_s # 1 byte saved!

Answer 8

Don't use the true and false keywords.

Use:

• !p for true (thanks, histocrat!)
• !0 for false. If all you need is a falsy value, then you can simply use p (which returns nil).

to save some chars.

• Martin Ender: Unless you actually need true (i.e. if a truthy value is enough, like in an if condition), you don't even need !!.

Answer 9

When you are using string interpolation, (as you should pr Martin Büttner's post), you don't need the curly brackets if your object has a sigil ($, @) in front of it. Useful for magical variables like $_, $&, 1ドル etc:

puts "this program has read #$. lines of input"

So also if you need to print a variable more than you use it otherwise, you may save some bytes.

a=42; puts "here is a: #{a}"; puts "here is a again: #{a}"
$b=43; puts "here is b: #$b"; puts "here is b again: #$b"

• vrintle: Isn't puts "here is b: "+b more shorter?
• daniero: @vrintle In this particular example, yes. But for instance "here is b:#{b}, here is a:#{a}!!" is shorter than "here is b:"+b+", here is a:"+a+"!!". The linked post also provides more info

Answer 10

New features in Ruby 2.3 and 2.4

It's good to stay abreast of new language features that will help your golf game. There are a few great ones in the latest Rubies.

Ruby 2.3

The safe navigation operator: &.

When you call a method that might return nil but you want to chain additional method calls if it's not, you waste bytes handling the nil case:

arr = ["zero", "one", "two"]
x = arr[5].size
# => NoMethodError: undefined method `size' for nil:NilClass
x = arr[5].size rescue 0
# => 0

The "safe navigation operator" stops the chain of method calls if one returns nil and returns nil for the whole expression:

x = arr[5]&.size || 0
# => 0

Array#dig & Hash#dig

Deep access to nested elements, with a nice short name:

o = { foo: [{ bar: ["baz", "qux"] }] }
o.dig(:foo, 0, :bar, 1) # => "qux"

Returns nil if it hits a dead end:

o.dig(:foo, 99, :bar, 1) # => nil

Enumerable#grep_v

The inverse of Enumerable#grep—returns all elements that don't match the given argument (compared with ===). Like grep, if a block is given its result is returned instead.

(1..10).grep_v 2..5 # => [1, 6, 7, 8, 9, 10]
(1..10).grep_v(2..5){|v|v*2} # => [2, 12, 14, 16, 18, 20]

Hash#to_proc

Returns a Proc that yields the value for the given key, which can be pretty handy:

h = { N: 0, E: 1, S: 2, W: 3 }
%i[N N E S E S W].map(&h)
# => [0, 0, 1, 2, 1, 2, 3]

Ruby 2.4

Ruby 2.4 isn't out yet, but it will be soon and has some great little features. (When it's released I'll update this post with some links to the docs.) I learned about most of these in this great blog post.

Enumerable#sum

No more arr.reduce(:+). You can now just do arr.sum. It takes an optional initial value argument, which defaults to 0 for Numeric elements ([].sum == 0). For other types you'll need to provide an initial value. It also accepts a block that will be applied to each element before addition:

[[1, 10], [2, 20], [3, 30]].sum {|a,b| a + b }
# => 66

Integer#digits

This returns an array of a number's digits in least-to-greatest significance order:

123.digits # => [3, 2, 1]

Compared to, say, 123.to_s.chars.map(&:to_i).reverse, this is pretty nice.

As a bonus, it takes an optional radix argument:

a = 0x7b.digits(16) # => [11, 7]
a.map{|d|"%x"%d} # => ["b", "7"]

Comparable#clamp

Does what it says on the tin:

v = 15
v.clamp(10, 20) # => 15
v.clamp(0, 10) # => 10
v.clamp(20, 30) # => 20

Since it's in Comparable you can use it with any class that includes Comparable, e.g.:

?~.clamp(?A, ?Z) # => "Z"

String#unpack1

A 2-byte savings over .unpack(...)[0]:

"👻💩".unpack(?U) # => [128123]
"👻💩".unpack(?U)[0] # => 128123
"👻💩".unpack1(?U) # => 128123

Precision argument for Numeric#ceil, floor, and truncate

Math::E.ceil(1) # => 2.8
Math::E.floor(1) # => 2.7
(-Math::E).truncate(1) # => -2.7

Multiple assignment in conditionals

This raises an error in earlier versions of Ruby, but is allowed in 2.4.

(a,b=1,2) ? "yes" : "no" # => "yes"
(a,b=nil) ? "yes" : "no" # => "no"

• Simply Beautiful Art: Golf Math::E.ceil(1) to Math::E.ceil 1, and likewise for floor and truncate.
• Jordan: @SimplyBeautifulArt I expect that someone golfing in Ruby will be able to make that leap themselves.
• Asone Tuhid: For Enumerable#sum, .flatten.sum is 2 bytes shorter than .sum{|a,b|a+b}
• Asone Tuhid: (-Math::E).truncate(1) is equivalent to -Math::E.truncate(1) which is 1 byte shorter
• Asone Tuhid: &. can be used with subscripting like this a&.[]i (1 byte shorter than a&.at i). Although, if brackets are required, a||a[i] is 1 byte is shorter than a&.[](i) or a&.at(i)

Answer 11

If you need to find if a particular element e is inside a range r, you can use

r===e

instead of the longer:

r.cover?(e) # only works if `r.exclude_end?` is false

or

r.member?(e)

or

r.include?(e)

• akuhn: Isn’t r===e even shorter?
• Cristian Lupascu: @akuhn Yes, it is. Much Shorter. Thanks for pointing that out, it helped me shorten my code by 10 chars, which is huge: codegolf.stackexchange.com/a/6125/3527
• akuhn: You’re welcome. Everything that can be used in a switch statement has === implemented.

Answer 12

Build arrays using a=i,*a to get them in reverse order. You don't even need to initialize a, and if you do it doesn't have to be an array.

Answer 13

Avoid length in if a.length<n

length is 6 bytes, a bit costly in code golf. in many situations, you can instead check if the array has anything at a given point. if you grab past the last index you will get nil, a falsey value.

So you can Change:

if a.length<5 to if !a[4] for -5 bytes

or

if a.length>5 to if a[5] for -6 bytes

or

if a.length<n to if !a[n-1] for -3 bytes

or

if a.length>n to if a[n] for -6 bytes

Note: will only work with an array of all truthy values. having nil or false within the array may cause problems.

• manatwork: I always use size... But this is definitely better. BTW, works for String too.
• G B: if !a[n-1] can be shortened to if !a[-n]

Answer 14

New features in Ruby 2.7 (experimental)

Ruby 2.7 is in prerelease (as of 17 Jun 2019) and has some features that look great for golfing. Note that some of them might not make it into the final 2.7 release.

All changes in Ruby 2.7-preview1: https://github.com/ruby/ruby/blob/v2_7_0_preview1/NEWS

Numbered block parameters

This is my favorite. It lets you finally drop the |a,b| in a block:

Edit: The syntax was changed from @1 to _1.

%w[a b c].zip(1..) { puts _1 * _2 }
# => a
# bb
# ccc

(削除) Method reference operator: .: (削除ここまで)

Edit: This was unfortunately removed before release.

.: is syntactic sugar for the .method method, e.g.:

(1..5).map(&1r.:/)
# => [(1/1), (1/2), (1/3), (1/4), (1/5)]

Pattern matching

I'm not sure how much use this will see in golf, but it's a great feature for which I only have a contrived example:

def div(*a)
 case a
 in [0, 0] then nil
 in [x, 0] if x > 0 then Float::INFINITY
 in [x, 0] then -Float::INFINITY
 in [x, y] then x.fdiv(y)
 end
end
div(-3, 0) # => -Infinity

The pattern matching syntax has lots of features. For a complete list, check out this presentation: https://speakerdeck.com/k_tsj/pattern-matching-new-feature-in-ruby-2-dot-7

This is also the feature most likely to change before 2.7 is finished; it even prints a warning when you try to use it, which you should heed:

warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!

Beginless Range: ..3

Analogous to the endless Range introduced in 2.6, it may or may not have much use in golfing:

%w[a v o c a d o].grep(..?m)
# => ["a", "c", "a", "d"]

Enumerable#tally to count like elements

This could be useful in golfing:

%w[a v o c a d o].tally
# => {"a"=>2, "v"=>1, "o"=>2, "c"=>1, "d"=>1}

Enumerable#filter_map to filter+map in one

(1..20).filter_map {|i| 10 * i if i.even? }
# => [20, 40, 60, 80, 100]

If the block returns nil or false the element will be omitted from the result.

Integer#[] takes a second argument or range:

You've long been able to get a specific bit from an integer with with subscript notation:

n = 77 # (binary 01001101)
n[3] # => 1

Now you can get the value of a range of bits by a second length argument or a range.

n = 0b01001101
n[2, 4] # => 3 (0011)
n[2..5] # => 3

Note that bits are indexed from least- to most-significant (right to left).

• Dingus: The range in the Enumerable#filter_map example should be (1..10), I think?
• histocrat: The method reference operator didn't make it in, as I sadly discovered just now trying to use it to do a restricted source challenge.
• Eric Duminil: @1 and @2 are apparently now _1 and _2.
• Mike: Unfortunatelly .: didn't make it through preview and was reverted in 2.7 release bugs.ruby-lang.org/issues/16275

Answer 15

$_ is last read line.

• print - if no argument given print content of $_
• ~/regexp/ - short for $_=~/regexp/

In Ruby 1.8, you have four methods in Kernel that operate on $_:

• chop
• chomp
• sub
• gsub

In Ruby 1.9, these four methods exist only if your script uses -n or -p.

If you want to print some variable often then use trace_var(:var_name){|a|p a}

• Darren Stone: These are only available when you run Ruby with the -p or -n option. Reference.
• daniero: It seems that trace_var only works with global $variables
• Dingus: Another trick that works with -n or -p is using a regexp literal as a boolean: the regexp is implicitly matched against $_. See this answer of mine for an example.
• Dingus: Unlike the String methods with the same names, the listed Kernel methods modify $_ in place. Generally this behaviour is what is wanted, but worth noting the difference.

Answer 16

Use string interpolation!

1. To replace to_s. If you need parentheses around whatever you want to turn into a string, to_s is two bytes longer than string interpolation:

   (n+10**i).to_s
   "#{n+10**i}"
   

2. To replace concatenation. If you concatenate something surrounded by two other strings, interpolation can save you one byte:

   "foo"+c+"bar"
   "foo#{c}bar"
   

   Also works if the middle thing is itself concatenated, if you just move the concatenation inside the interpolation (instead of using multiple interpolations):

   "foo"+c+d+e+"bar"
   "foo#{c+d+e}bar"
   

Answer 17

Don't use #each. You can loop over all elements just fine with #map. So instead of

ARGV.each{|x|puts x}

you can do the same in less bytes.

ARGV.map{|x|puts x}

Of course, in this case puts $* would be even shorter.

---

There are literals for rational and complex numbers:

puts 3/11r == Rational(3,11)
puts 3.3r == Rational(66,20)
puts 1-1.i == Complex(1,-1)
=> true
true
true

---

You can use most bytes within strings. "\x01" (6 bytes) can be shortened to "" (3 bytes). If you only need this one byte, this can be shortened even further to ? (2 bytes).

By the same token, you can get newlines shorter like this:

(0..10).to_a.join'
'
 => "0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10"

You can use ?\n and ?\t as well, which is one byte shorter than "\n" and "\t". For obfuscation, there also ?\s, a space.

---

Use constants instead of passing arguments around, even if you need to change them. The interpreter will give warnings to stderr, but who cares. If you need to define more variables related to each other, you can chain them like this:

A=C+B=7+C=9
=> A=17, B=16, C=9

This is shorter than C=9;B=16;A=17 or C=0;B=C+7;A=C+B.

---

If you need an infinite loop, use loop{...}. Loops of unknown length may be shorter with other loops:

loop{break if'
'==f(gets)}
while'
'!=f(gets);end

---

Some more gsub/regexp tricks. Use the special '1円' escape characters instead of a block:

"golf=great short=awesome".gsub(/(\w+)=(\w+)/,'(1円~>2円)')
"golf=great short=awesome".gsub(/(\w+)=(\w+)/){"(#{1ドル}~>#{2ドル})")

And the special variables 1ドル etc. if you need to perform operations. Keep in mind they are defined not only inside the block:

"A code-golf challenge." =~ /(\w+)-(\w+)/
p [1,ドル2,ドル$`,$']
=> ["code", "golf", "A ", " challenge."] 

---

Get rid of spaces, newlines, and parentheses. You can omit quite a bit in ruby. If in doubt, always try if it works without, and keep in mind this might break some editor syntax highlighting...

x+=1if$*<<A==????::??==??

• Martin Ender: "Please post one tip per answer." Also ?\n is nice, but not really shorter than actually putting a newline character inside quotes. (same for tab)
• Cyoce: And puts$* is even shorter.
• Asone Tuhid: I know you were trying to prove a point but I'm pretty sure that last example is the same as x+=1;$*<<A

Answer 18

If you ever need to get a number from ARGV, get, or something similar to do something that many times, instead of calling to_i on it, you can just use ?1.upto x{do something x times} where x is a string.

So using ?1.upto(a){} instead of x.to_i.times{} will save you 2 characters.

You can also re-write things like p 1 while 1 or p 1 if 1 as p 1while 1 or p 1if 1

That example isn't very useful, but it could be used for other things.

Also, if you need to assign the first element of an array to a variable, a,=c will save two characters as opposed to a=c[0]

Answer 19

Save some bytes when removing repeated elements of an array

a.uniq # before
a|[] # after
 ^^

If you will be using an empty array [] in a variable, you can save even more bytes:

a.uniq;b=[] # before
a|b=[] # after
 ^^^^^

• Asone Tuhid: For the first case, a&a is 1 byte shorter

Answer 20

Scientific notation can often be used to shave off a char or two:

x=1000
#versus
x=1e3

• Dogbert: Note: This will return a Float value (1000.0) instead of an Integer, which may cause inaccurate results with large numbers.
• Phrogz: Ah, nice 1e2 is better than 100.0 when a percentage is needed.
• Unihedron: Similar to this principle, 1.0* is 1 char shorter than .to_f
• Dingus: To my surprise, this trick works with Integer#upto and Integer#downto, e.g. 1.upto(1000) can become 1.upto(1e3). (Both forms iterate over integers.)

Answer 21

Kernel#p is a fun method.

Use p var instead of puts var. This works perfectly with integers and floats, but not with all types. It prints quotation marks around strings, which is probably not what you want.

Used with a single argument, p returns the argument after printing it.

Used with multiple arguments, p returns the arguments in an array.

Use p (with no arguments) instead of nil.

• Patrick Oscity: Unfortunately p 'some string' prints "some string" and not just some string which is often criticised by others.
• Cyoce: Basically p s is the same as puts s.inspect, but it returns s

Answer 22

Yet another way to use the splat operator: if you want to assign a single array literal, a * on the left-hand side is shorter than brackets on the right-hand side:

a=[0]
*a=0

With multiple values you don't even need the splat operator (thanks to histocrat for correcting me on that):

a=[1,2]
a=1,2

• histocrat: The latter case doesn't actually need the splat.
• Martin Ender: @histocrat Oh wow, I thought the second value would just be discarded in that case.
• Doorknob: I can't believe I haven't known these in all the time I've spent golfing in Ruby.

Answer 23

To join an array, instead of this

[...].join

do this

[...]*''

which saves 2 bytes. To join with a separator use

[...]*?,

Answer 24

Save a byte when printing a word with symbols

This is a bit situational, but every byte counts!

puts"thing" # before
puts:thing # after
 ^

Answer 25

Avoid Array#repeated_permutation and Array#repeated_combination

Credit to @AsoneTuhid who golfed the code for repeated permutations of length \$\ge5\$.

Some of Ruby's built-in methods have unfortunately long names. Never use Array#repeated_permutation or Array#repeated_combination; save bytes as follows.

Repeated permutations

Assume a is an array. To get repeated permutations of length \$L = n + 1\$ of the elements of a:

a.product(a,a,a) # L <= 4; number of arguments = n
a.product(*[a]*n) # L >= 5

Depending on context, the parentheses may not be required. Both of the above yield an array. To iterate over the permutations, simply call with a block.

Repeated combinations

For repeated combinations of length \$L\$, use one of

a.send(a.methods[42],L) # enumerator
[*a.send(a.methods[42],L)] # array

The index that yields :repeated_combination depends on the Ruby version and possibly the OS (42 is correct for Ruby 2.5.5 on Linux, which is the version on TIO at the time of writing). The default indexing may also be disrupted if any libraries are loaded. The correct index in any case can always be found using [].methods.index(:repeated_combination).

---

In general, calling a method by index using Object#send and Object#methods, as demonstrated above for repeated combinations, is shorter than a direct method call when the number of bytes in the method name and the index of the method in the methods array satisfy:

+-------+-------+
| Bytes | Index |
+-------+-------+
| 19+ | 0-9 |
| 20+ | 10-99 |
| 21+ | 100+ |
+-------+-------+
Subtract 1 from byte count if parentheses not needed for send.

• Asone Tuhid: 17 bytes
• Dingus: @AsoneTuhid Very nice. Seems so obvious now that I see it. Thanks!

Answer 26

Use Goruby instead of Ruby, which is something like an abbreviated version of Ruby. You can install it with rvm via

rvm install goruby

Goruby allows you to write most of your code as you would be writing Ruby, but has additional abbreviations built in. To find out the shortest available abbreviation for something, you can use the helper method shortest_abbreviation, for example:

shortest_abbreviation :puts
#=> "pts"
Array.new.shortest_abbreviation :map
#=> "m"
String.new.shortest_abbreviation :capitalize
#=> "cp"
Array.new.shortest_abbreviation :join
#=> "j"

Also very handy is the alias say for puts which itself can be abbreviated with s. So instead of

puts [*?a..?z].map(&:capitalize).join

you can now write

s [*?a..?z].m(&:cp).j

to print the alphabet in capitals (which is not avery good example). This blog post explains more stuff and some of the inner workings if you are interested in further reading.

PS: don't miss out on the h method ;-)

• undergroundmonorail: More than 2 years later and I finally figured out what this answer reminds me of...

Answer 27

I just attempted a TDD code-golf challenge i.e. Write shortest code to make specs pass. The specs were something like

describe PigLatin do
 describe '.translate' do
 it 'translates "cat" to "atcay"' do
 expect(PigLatin.translate('cat')).to eq('atcay')
 end
 # And similar examples for .translate
 end
end

For the sake of code-golf, one need not create a module or class.

Instead of

module PigLatin def self.translate s;'some code'end;end

one can do

def(PigLatin=p).translate s;'some code'end

Saves 13 characters!

• histocrat: Ha, very thorough. Not only did you add the necessary behavior to PigLatin, but also to @pig_latin, $pig_latin, and 'pig'['latin'].
• Eric Duminil: @histocrat: Now I get it. It's because translate has been defined on nil.

Answer 28

When a challenge requires that you output multiple lines, you don't have to loop through your results in order to print each line of e.g. an array. The puts method will flatten an array and print each element on a separate line.

> a = %w(testing one two three)
> puts a
testing
one
two
three

Combining the splat operator with #p you can make it even shorter:

p *a

The splat operator (technically the *@ method, I think) also casts your non-array enumerables to arrays:

> p a.lazy.map{|x|x*2}
#<Enumerator::Lazy: #<Enumerator::Lazy: [1, 2, 3]>:map>

vs

> p *a.lazy.map{|x|x*2}
2
4
6

• Asone Tuhid: *@ is not a method, splat is syntactic sugar

Answer 29

Subscripting Numbers!

I just discovered this yesterday. n[i] returns n's bit at the i-th position. Example:

irb(main):001:0> n = 0b11010010
=> 210
irb(main):002:0> n[0]
=> 0
irb(main):003:0> n[1]
=> 1
irb(main):004:0> n[2]
=> 0
irb(main):005:0> n[3]
=> 0
irb(main):006:0> n[4]
=> 1
irb(main):007:0> n[5]
=> 0

• Simply Beautiful Art: And now you can use more arguments such as n[0..3]

Answer 30

On looping

while...end

If you need to break out of the loop, while condition;code;end will probably be shorter than loop{code;condition||break}.

The ; before end is not always required, eg. while condition;p("text")end

until c;...;end is equivalent to while !c;...;end and 1 byte shorter.

Note that in most cases code while condition and code until condition are significantly shorter as they don't require the end keyword and can often drop semicolons. Also, i+=1 while true is equivalent to i+=1while true and 1 byte shorter.

redo

When run, the redo command jumps back to the beginning of the block it's in.

When using redo in a lambda, you will have to move any setup variables to the arguments to avoid them being reset at every iteration (see examples).

recursion

Recursion can be shorter is some cases. For instance, if you're working on an array element by element, something like f=->s,*t{p s;t[0]&&f[*t]} can be shorter than the alternatives depending on the stuff.

Note that per the current consensus, if you're calling your function by name, you need to include the assignment (f=) in the byte count making all recursive lambdas 2 bytes longer by default.

eval

If you need to run some code n times, you can use eval"code;"*n.

This will concatenate code; n times and run the whole thing.

Note that in most cases you need to include a ; after your code.

Examples

A lambda to print all numbers from 1 to a inclusive:

->n{i=0;loop{p i+=1;i<n||break}} # 32 bytes
f=->n,i=1{i>n||p(i)&&f[n,i+1]} # 30 bytes
->n,i=0{p(i+=1)<n&&redo} # 24 bytes
->n{i=0;p i+=1while i<n} # 24 bytes
->n{i=0;eval"p i+=1;"*n} # 24 bytes
->n{n.times{|i|p i+1}} # 22 bytes # thanks to @benj2240
->n{n.times{p _1+1}} # 20 bytes # thanks to @AgentIvan

In this case, since the end-point is defined (n), the n.times loop is the shortest.

The redo loop works because i+=1 modifies i and returns its new value and p(x) returns x (this is not true of print and puts).

Given a function g and a number n, find the first number strictly larger than n for which g[n] is truthy

->g,n{loop{g[n+=1]&&break};n} # 29 bytes
f=->g,n{g[n+=1]?n:f[g,n]} # 25 bytes
->g,n{1until g[n+=1];n} # 23 bytes
->g,n{(n+1..).find &g} # 22 bytes
->g,n{g[n+=1]?n:redo} # 21 bytes

In this case, with an unknown end-point, redo is the best option.

The (n+1..Inf) loop is equivalent to simply looping indefinitely but more verbose.

A 1 (or anything else) is required before the until keyword to complete the syntax, using a number allows you to drop a space.

The eval method is not viable in this case because there is neither a defined end-point nor an upper bound.

Update: with the new open ranges (n+1..Inf) can be written simply as (n+1..), also .find{|x|g[x]} is equivalent to .find &g where g is converted to a block.

TL;DR check out redo, it can very often shave off a couple of bytes

• benj2240: .times can often be even shorter for fixed loops, eg ->n{n.times{|i|p i+1}} for 22 bytes