Programming Forums > Script Programming > Ruby

Jessehk · Apr 14th, 2006, 11:21 AM

I just thought I'd include a few uses of Inumerable#inject.

http://ruby-doc.org/core/

It's pretty neat.

sum:

(1..10).inject { |sum, elem| sum + elem } #=> 55

factorial:

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(1..6).inject(1) { |product, elem| product * elem } #=> 720

fill an array (like the functional map):

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(1..10).inject([]) { |result, elem| result << elem ** 2 } 
#=> [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

searching for a value:

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%w(This is a wonderful test).inject { |big, word| word.length > big.length? word : big }
#=> "wonderful"

Master · Apr 14th, 2006, 11:37 AM

I guess you still don't understand ruby quite well. When you defualt parameter is an hash. then you pass just :a=>1, that mean you are replacing the defualt hash with the one which you pass that contains only a, by passing hash as the defualt parameter, your argument can be over millions if you want, all it will basically do is put all those million of values into an hash and print just the one you said it should print. you passing :a=>1 mean nothing to the hash defualt, i can even use "45"=> "myName" and it will accept it. you can print out all the hash
by using
myhash.values or myhash.keys

Jessehk · Apr 15th, 2006, 12:02 AM

Master is right.

The correct way to do it is like this:

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def func(args = {:a => 2, :b => 3}) #default values
    puts "a: #{a}\nb: #{b}"
end

func(:a => 3, :b => 4)
#=> a: 3
#     b: 4

Dietrich · Apr 15th, 2006, 5:07 AM

Jessehk,
thanks for your inject examples, they are pretty neat!

On the default argument discussion, I get stuck with the fact that you only get the correct defaults, if you don't use any arguments at all.

Dietrich · Apr 15th, 2006, 6:23 AM

Keep finding these strange things:

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puts c = !c  # true

Jessehk · Apr 15th, 2006, 9:48 AM

Quote:

Originally Posted by Dietrich

Jessehk,

On the default argument discussion, I get stuck with the fact that you only get the correct defaults, if you don't use any arguments at all.

The reason is that default arguments are a bit of a hack. Basically, you're telling the method to accept a hash. That hash could consist of any keys and values the user chooses.

Like I said though, named arguments are planned (or so I hear) for the 2.0 release.

Jessehk · Jun 22nd, 2006, 11:49 AM

I was just searching through the API documentation at http://ruby-doc.org and I found a really cool trick with Integer#to_s

If you use it normally, like so:

(Toggle Plain Text)

>> 3.to_s
=> "3"
>> 100.to_s
=> "100"

you get results as expected. What I didn't realize is that if supply an Integer from 1 to 36, it will convert the number to that base.

(Toggle Plain Text)

>> 33.to_s(2) #base 2, or binary
=> "100001"
>> 33.to_s(8) #base 8, or octal
=> "41"
>> 31231313113123.to_s(16) #base 16, or hexadecimal
=> "1c679b52f023"
>> 31313231312.to_s(36) #base 36, the largest supported
=> "edv37ww"

I thought it was neat.

Jessehk · Jul 8th, 2006, 8:40 PM

This trick is just cool.

Imagine being able to do things like this:

(Toggle Plain Text)

["Joe", "Sally", "Phil"].map(&:upcase) #=> ["JOE", "SALLY", "PHIL"]

With this snippet, you can. I did not think of this.

(Toggle Plain Text)

class Symbol
    def to_proc
        lambda { |obj, *args| obj.send(self, *args) }
    end
end

Example usage:

(Toggle Plain Text)

require 'jesse_symbol' #where new code is stored

class Integer
    def square
        self * self
    end
end

p (1..10).map(&:square)

#or even
p (1..10).inject(&:+) #sum
p (1..10).inject(&:*) #product

Full explanation: http://blogs.pragprog.com/cgi-bin/pr...by/ToProc.rdoc

Dietrich · Jul 9th, 2006, 11:02 AM

Jessehk, great hints of nice code! Also the URLs, Thanks

Dietrich · Jul 9th, 2006, 2:51 PM

I found this simple example:

(Toggle Plain Text)

# an array of the 50 states

states50 = [
  'Alabama', 'Alaska', 'Arizona', 'Arkansas', 'California', 
  'Colorado', 'Connecticut', 'Delaware', 'Florida', 'Georgia', 
  'Hawaii', 'Idaho', 'Illinois', 'Indiana', 'Iowa', 'Kansas', 
  'Kentucky', 'Louisiana', 'Maine', 'Maryland', 'Massachusetts', 
  'Michigan', 'Minnesota', 'Mississippi', 'Missouri', 'Montana', 
  'Nebraska', 'Nevada', 'New_Hampshire', 'New_Jersey', 'New_Mexico',
  'New_York', 'North_Carolina', 'North_Dakota', 'Ohio', 'Oklahoma', 
  'Oregon', 'Pennsylvania', 'Rhode_Island', 'South_Carolina', 
  'South_Dakota', 'Tennessee', 'Texas', 'Utah', 'Vermont', 
  'Virginia', 'Washington', 'West_Virginia', 'Wisconsin', 'Wyoming'
]

puts states50.length()  # () is optional  --> 50

puts states50  # displays 50 states, one per line

def find(arr, value)
  for i in 0...arr.length
    return i if value == arr[i]
  end
end

puts find(states50, "Iowa")  # found at index --> 14

Apr 14th, 2006, 11:21 AM	#21
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 648 Rep Power: 4	I just thought I'd include a few uses of Inumerable#inject. http://ruby-doc.org/core/ It's pretty neat. sum: (Toggle Plain Text) (1..10).inject { \|sum, elem\| sum + elem } #=> 55 (1..10).inject { \|sum, elem\| sum + elem } #=> 55 factorial: (Toggle Plain Text) (1..6).inject(1) { \|product, elem\| product * elem } #=> 720 (1..6).inject(1) { \|product, elem\| product * elem } #=> 720 fill an array (like the functional map): (Toggle Plain Text) (1..10).inject([]) { \|result, elem\| result << elem 2 } #=> [1, 4, 9, 16, 25, 36, 49, 64, 81, 100] (1..10).inject([]) { \|result, elem\| result << elem 2 } #=> [1, 4, 9, 16, 25, 36, 49, 64, 81, 100] searching for a value: (Toggle Plain Text) %w(This is a wonderful test).inject { \|big, word\| word.length > big.length? word : big } #=> "wonderful" %w(This is a wonderful test).inject { \|big, word\| word.length > big.length? word : big } #=> "wonderful" __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Apr 15th, 2006, 12:02 AM	#23
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 648 Rep Power: 4	Master is right. The correct way to do it is like this: (Toggle Plain Text) def func(args = {:a => 2, :b => 3}) #default values puts "a: #{a}\nb: #{b}" end func(:a => 3, :b => 4) #=> a: 3 # b: 4 def func(args = {:a => 2, :b => 3}) #default values puts "a: #{a}\nb: #{b}" end func(:a => 3, :b => 4) #=> a: 3 # b: 4 __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Apr 15th, 2006, 5:07 AM	#24
Dietrich Professional Programmer Join Date: Feb 2005 Posts: 434 Rep Power: 4	Jessehk, thanks for your inject examples, they are pretty neat! On the default argument discussion, I get stuck with the fact that you only get the correct defaults, if you don't use any arguments at all. __________________ I looked it up on the Intergnats!

Apr 15th, 2006, 6:23 AM	#25
Dietrich Professional Programmer Join Date: Feb 2005 Posts: 434 Rep Power: 4	Keep finding these strange things: (Toggle Plain Text) puts c = !c # true puts c = !c # true __________________ I looked it up on the Intergnats!

Jun 22nd, 2006, 11:49 AM	#27
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 648 Rep Power: 4	I was just searching through the API documentation at http://ruby-doc.org and I found a really cool trick with Integer#to_s If you use it normally, like so: (Toggle Plain Text) >> 3.to_s => "3" >> 100.to_s => "100" >> 3.to_s => "3" >> 100.to_s => "100" you get results as expected. What I didn't realize is that if supply an Integer from 1 to 36, it will convert the number to that base. (Toggle Plain Text) >> 33.to_s(2) #base 2, or binary => "100001" >> 33.to_s(8) #base 8, or octal => "41" >> 31231313113123.to_s(16) #base 16, or hexadecimal => "1c679b52f023" >> 31313231312.to_s(36) #base 36, the largest supported => "edv37ww" >> 33.to_s(2) #base 2, or binary => "100001" >> 33.to_s(8) #base 8, or octal => "41" >> 31231313113123.to_s(16) #base 16, or hexadecimal => "1c679b52f023" >> 31313231312.to_s(36) #base 36, the largest supported => "edv37ww" I thought it was neat. __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Apr 14th, 2006, 11:37 AM	#22
Master Programmer Join Date: Sep 2005 Location: GA Posts: 99 Rep Power: 4	I guess you still don't understand ruby quite well. When you defualt parameter is an hash. then you pass just :a=>1, that mean you are replacing the defualt hash with the one which you pass that contains only a, by passing hash as the defualt parameter, your argument can be over millions if you want, all it will basically do is put all those million of values into an hash and print just the one you said it should print. you passing :a=>1 mean nothing to the hash defualt, i can even use "45"=> "myName" and it will accept it. you can print out all the hash by using myhash.values or myhash.keys

Jul 8th, 2006, 8:40 PM	#28
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 648 Rep Power: 4	This trick is just cool. Imagine being able to do things like this: (Toggle Plain Text) ["Joe", "Sally", "Phil"].map(&:upcase) #=> ["JOE", "SALLY", "PHIL"] ["Joe", "Sally", "Phil"].map(&:upcase) #=> ["JOE", "SALLY", "PHIL"] With this snippet, you can. I did *not* think of this. (Toggle Plain Text) class Symbol def to_proc lambda { \|obj, args\| obj.send(self, args) } end end class Symbol def to_proc lambda { \|obj, args\| obj.send(self, args) } end end Example usage: (Toggle Plain Text) require 'jesse_symbol' #where new code is stored class Integer def square self * self end end p (1..10).map(&:square) #or even p (1..10).inject(&:+) #sum p (1..10).inject(&:) #product require 'jesse_symbol' #where new code is stored class Integer def square self self end end p (1..10).map(&:square) #or even p (1..10).inject(&:+) #sum p (1..10).inject(&:*) #product Full explanation: http://blogs.pragprog.com/cgi-bin/pr...by/ToProc.rdoc __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Jul 9th, 2006, 11:02 AM	#29
Dietrich Professional Programmer Join Date: Feb 2005 Posts: 434 Rep Power: 4	Jessehk, great hints of nice code! Also the URLs, Thanks __________________ I looked it up on the Intergnats!

Jul 9th, 2006, 2:51 PM	#30
Dietrich Professional Programmer Join Date: Feb 2005 Posts: 434 Rep Power: 4	I found this simple example: (Toggle Plain Text) # an array of the 50 states states50 = [ 'Alabama', 'Alaska', 'Arizona', 'Arkansas', 'California', 'Colorado', 'Connecticut', 'Delaware', 'Florida', 'Georgia', 'Hawaii', 'Idaho', 'Illinois', 'Indiana', 'Iowa', 'Kansas', 'Kentucky', 'Louisiana', 'Maine', 'Maryland', 'Massachusetts', 'Michigan', 'Minnesota', 'Mississippi', 'Missouri', 'Montana', 'Nebraska', 'Nevada', 'New_Hampshire', 'New_Jersey', 'New_Mexico', 'New_York', 'North_Carolina', 'North_Dakota', 'Ohio', 'Oklahoma', 'Oregon', 'Pennsylvania', 'Rhode_Island', 'South_Carolina', 'South_Dakota', 'Tennessee', 'Texas', 'Utah', 'Vermont', 'Virginia', 'Washington', 'West_Virginia', 'Wisconsin', 'Wyoming' ] puts states50.length() # () is optional --> 50 puts states50 # displays 50 states, one per line def find(arr, value) for i in 0...arr.length return i if value == arr[i] end end puts find(states50, "Iowa") # found at index --> 14 # an array of the 50 states states50 = [ 'Alabama', 'Alaska', 'Arizona', 'Arkansas', 'California', 'Colorado', 'Connecticut', 'Delaware', 'Florida', 'Georgia', 'Hawaii', 'Idaho', 'Illinois', 'Indiana', 'Iowa', 'Kansas', 'Kentucky', 'Louisiana', 'Maine', 'Maryland', 'Massachusetts', 'Michigan', 'Minnesota', 'Mississippi', 'Missouri', 'Montana', 'Nebraska', 'Nevada', 'New_Hampshire', 'New_Jersey', 'New_Mexico', 'New_York', 'North_Carolina', 'North_Dakota', 'Ohio', 'Oklahoma', 'Oregon', 'Pennsylvania', 'Rhode_Island', 'South_Carolina', 'South_Dakota', 'Tennessee', 'Texas', 'Utah', 'Vermont', 'Virginia', 'Washington', 'West_Virginia', 'Wisconsin', 'Wyoming' ] puts states50.length() # () is optional --> 50 puts states50 # displays 50 states, one per line def find(arr, value) for i in 0...arr.length return i if value == arr[i] end end puts find(states50, "Iowa") # found at index --> 14 __________________ I looked it up on the Intergnats!

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