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I'am trying to figure out ObjectSpace.each_object
In console:
class Foo; end
Foo.new
ObjectSpace.each_object(Foo).count
=> 1
GC.start
ObjectSpace.each_object(Foo).count
=> 1
I've seen examples and I know that the second count should be 0.
Any ideas what is going on here?
Thanks.
It depends on your console.
IRB
The last result is saved as _, even if it hasn't been explicitely assigned.
Running GC.start won't remove the last object :
irb(main):001:0> class Foo; end
=> nil
irb(main):002:0>
irb(main):003:0* Foo.new
=> #<Foo:0x007fca7a309f98>
irb(main):004:0> p ObjectSpace.each_object(Foo).count; GC.start; p ObjectSpace.each_object(Foo).count
1
1
=> 1
irb(main):005:0> p ObjectSpace.each_object(Foo).count; GC.start; p ObjectSpace.each_object(Foo).count
1
0
=> 0
Pry
You can access the last result and the second to last result with _ and __ :
[1] pry(main)> 'a'
=> "a"
[2] pry(main)> 'b'
=> "b"
[3] pry(main)> p _, __
"b"
"a"
=> ["b", "a"]
Pry saves all the 100 last results in _out_ Pry::HistoryArray:
[1] pry(main)> class Foo; end
=> nil
[2] pry(main)> Foo.new
=> #<Foo:0x007fd093102118>
[3] pry(main)> ObjectSpace.each_object(Foo).count
=> 1
[4] pry(main)> GC.start
=> nil
[5] pry(main)> ObjectSpace.each_object(Foo).count
=> 1
[6] pry(main)> _out_[2]
=> #<Foo:0x007fd093102118>
You can use _out_.pop! to remove its last element :
[1] pry(main)> class Foo; end
=> nil
[2] pry(main)> Foo.new
=> #<Foo:0x007fa90b1ad360>
[3] pry(main)> ObjectSpace.each_object(Foo).count
=> 1
[4] pry(main)> GC.start
=> nil
[5] pry(main)> ObjectSpace.each_object(Foo).count
=> 1
[6] pry(main)> 5.times{_out_.pop!}
=> 5
[7] pry(main)> GC.start
=> nil
[8] pry(main)> ObjectSpace.each_object(Foo).count
=> 0
Inside a script
If you execute :
class Foo; end
Foo.new
p ObjectSpace.each_object(Foo).count
GC.start
p ObjectSpace.each_object(Foo).count
inside a script, you get :
1
0
GC.start does not force the garbage collector to start.
It is slightly unclear from the documentation, but it just instructs the engine to schedule a garbage collection. That said, one can not rely on GC.start would immediately remove objects from the heap.
I have two numbers of different length:
"103" and "11"
In irb:
2.1.1 :005 > "11" > "103"
=> true
2.1.1 :006 > "11" < "103"
=> false
Why does this happen? I understand I can to a .to_i for each string, but if this is a rails query where the column type is string, anything I can do about this?
Strings are sorted lexicographically which means that "1" comes after "0", and "103" comes before "11", and before "1122344", and before "1abc".
You cannot compare strings as if they were numbers, you need to parse them as numbers before you can do that.
The only way I can think of, is to make sure they are padded with enough zeroes before they are turned into a string: "000103", "000011"...
Strings are being compared character by character. Hence '11' > '103' execution stops on a second character and returns true, since '1'.chr > '0'.chr
They are strings. And they are compared by String#ord value.
So '1'.ord # => 49 and '0'.ord # => 48. That is why
'11' > '10' # => true
# and
'11' > '100' # => true
as well as
'b' > 'a' # => true
'a'.ord # => 97
'b'.ord # => 98
# and
'b' > 'aaaaa' # => still true
I am getting TypeError: can't convert String into Integer, I found duplicate answer too, but I am facing this error for 'pack'.
Other confusion is, it is working fine with ruby 1.8.7, not with ruby 1.9.3, here is the code, I am using jruby1.7.2
irb(main):003:0> length=nil
=> nil
irb(main):004:0> token_string ||= ["A".."Z","a".."z","0".."9"].collect { |r| r.to_a }.join + %q(!$:*)
=> "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!$:*"
irb(main):005:0> token = (0..(length ? length : 60)).collect { token_string[rand( token_string.size)]}.pack("c*")
TypeError: can't convert String into Integer
from (irb):5:in `pack'
from (irb):5
from /home/appandya/.rvm/rubies/ruby-1.9.3-p374/bin/irb:13:in `<main>'
irb(main):006:0>
Any Idea?
string[x] in Ruby 1.8 gives you a Fixnum (the character code) and in 1.9 it gives you a single character string.
Array#pack turns an array into a binary sequence. The "c*" template to pack converts an array of Ruby integers into a stream of 8-bit signed words.
Here are the solutions, those comes from the Google Groups
1.
Background
>> %w(a b c).pack('*c')
TypeError: can't convert String into Integer
from (irb):1:in `pack'
from (irb):1
from /usr/bin/irb:12:in `<main>'
>> [1, 2, 3].pack('*c')
=> "\x01"
>> %w(a b c).map(&:ord).pack('*c')
=> "a"
Solution
irb(main):001:0> length=nil
=> nil
irb(main):002:0> token_string ||= ["A".."Z","a".."z","0".."9"].collect { |r| r.to_a }.join + %q(!$:*)
=> "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!$:*"
irb(main):003:0> (0..(length ? length : 60)).collect { token_string[rand( token_string.size)]}.map(&:ord).pack("c*")
=> "rd!:!LcxU3ON57*t2s520v*zvvdflSNAgU6uq14SiD00VUDlm9:4:tJz5Ri5o"
irb(main):004:0>
2.
The return type of String's [] function was Fixnum in 1.8 but is String in 1.9:
>JRUBY_OPTS=--1.9 ruby -e "puts 'a'[0].class"
String
>JRUBY_OPTS=--1.8 ruby -e "puts 'a'[0].class"
Fixnum
JRuby 1.7.x defaults to acting like Ruby 1.9.3. You need to set JRUBY_OPTS.
3.
try join instead of pack
irb(main):004:0> length=nil
=> nil
irb(main):005:0> token_string ||= ["A".."Z","a".."z","0".."9"].collect { |r| r.to_a }.join + %q(!$:*)
=> "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!$:*"
irb(main):006:0> token = (0..(length ? length : 60)).collect { token_string[rand( token_string.size)]}.join("c*")
=> "Fc*Dc*1c*6c*ac*Kc*Tc*Qc*Hc*jc*Ec*Kc*kc*zc*sc*3c*ic*hc*kc*wc**c*Wc*$c*Kc*Ic*Uc*Cc*bc*Pc*1c*!c*mc*Bc*lc*dc*ic*Dc*sc*Ac*Bc*nc*Kc*mc*Lc*oc*Zc*Xc*jc*6c*2c*Uc*ec*Yc*Dc*vc*Ic*Uc*5c*Zc*3c*o"
irb(main):007:0>
4.
if you're just trying to make a string of random characters that are 8-bit clean you may want to look at Random#bytes and something like Base64.encode64.
5.
active_support/secure_random also has a nice API for these things
I would recommend you take a look at: Array Method Pack, essentially the .pack("c") expects the elements of the array to be integers. You could try .pack("a*")
Use token = (0..(length ? length : 60)).collect { token_string[rand( token_string.size)]}.pack("a"*61)
You get the same result. I am using 61 because, going from 0..60 has 61 elements.
To add a new pair to Hash I do:
{:a => 1, :b => 2}.merge!({:c => 3}) #=> {:a => 1, :b => 2, :c => 3}
Is there a similar way to delete a key from Hash ?
This works:
{:a => 1, :b => 2}.reject! { |k| k == :a } #=> {:b => 2}
but I would expect to have something like:
{:a => 1, :b => 2}.delete!(:a) #=> {:b => 2}
It is important that the returning value will be the remaining hash, so I could do things like:
foo(my_hash.reject! { |k| k == my_key })
in one line.
Rails has an except/except! method that returns the hash with those keys removed. If you're already using Rails, there's no sense in creating your own version of this.
class Hash
# Returns a hash that includes everything but the given keys.
# hash = { a: true, b: false, c: nil}
# hash.except(:c) # => { a: true, b: false}
# hash # => { a: true, b: false, c: nil}
#
# This is useful for limiting a set of parameters to everything but a few known toggles:
# #person.update(params[:person].except(:admin))
def except(*keys)
dup.except!(*keys)
end
# Replaces the hash without the given keys.
# hash = { a: true, b: false, c: nil}
# hash.except!(:c) # => { a: true, b: false}
# hash # => { a: true, b: false }
def except!(*keys)
keys.each { |key| delete(key) }
self
end
end
Why not just use:
hash.delete(key)
hash is now the "remaining hash" you're looking for.
Oneliner plain ruby, it works only with ruby > 1.9.x:
1.9.3p0 :002 > h = {:a => 1, :b => 2}
=> {:a=>1, :b=>2}
1.9.3p0 :003 > h.tap { |hs| hs.delete(:a) }
=> {:b=>2}
Tap method always return the object on which is invoked...
Otherwise if you have required active_support/core_ext/hash (which is automatically required in every Rails application) you can use one of the following methods depending on your needs:
➜ ~ irb
1.9.3p125 :001 > require 'active_support/core_ext/hash' => true
1.9.3p125 :002 > h = {:a => 1, :b => 2, :c => 3}
=> {:a=>1, :b=>2, :c=>3}
1.9.3p125 :003 > h.except(:a)
=> {:b=>2, :c=>3}
1.9.3p125 :004 > h.slice(:a)
=> {:a=>1}
except uses a blacklist approach, so it removes all the keys listed as args, while slice uses a whitelist approach, so it removes all keys that aren't listed as arguments. There also exist the bang version of those method (except! and slice!) which modify the given hash but their return value is different both of them return an hash. It represents the removed keys for slice! and the keys that are kept for the except!:
1.9.3p125 :011 > {:a => 1, :b => 2, :c => 3}.except!(:a)
=> {:b=>2, :c=>3}
1.9.3p125 :012 > {:a => 1, :b => 2, :c => 3}.slice!(:a)
=> {:b=>2, :c=>3}
There are many ways to remove a key from a hash and get the remaining hash in Ruby.
.slice => It will return selected keys and not delete them from the original hash. Use slice! if you want to remove the keys permanently else use simple slice.
2.2.2 :074 > hash = {"one"=>1, "two"=>2, "three"=>3}
=> {"one"=>1, "two"=>2, "three"=>3}
2.2.2 :075 > hash.slice("one","two")
=> {"one"=>1, "two"=>2}
2.2.2 :076 > hash
=> {"one"=>1, "two"=>2, "three"=>3}
.delete => It will delete the selected keys from the original hash(it can accept only one key and not more than one).
2.2.2 :094 > hash = {"one"=>1, "two"=>2, "three"=>3}
=> {"one"=>1, "two"=>2, "three"=>3}
2.2.2 :095 > hash.delete("one")
=> 1
2.2.2 :096 > hash
=> {"two"=>2, "three"=>3}
.except => It will return the remaining keys but not delete anything from the original hash. Use except! if you want to remove the keys permanently else use simple except.
2.2.2 :097 > hash = {"one"=>1, "two"=>2, "three"=>3}
=> {"one"=>1, "two"=>2, "three"=>3}
2.2.2 :098 > hash.except("one","two")
=> {"three"=>3}
2.2.2 :099 > hash
=> {"one"=>1, "two"=>2, "three"=>3}
.delete_if => In case you need to remove a key based on a value. It will obviously remove the matching keys from the original hash.
2.2.2 :115 > hash = {"one"=>1, "two"=>2, "three"=>3, "one_again"=>1}
=> {"one"=>1, "two"=>2, "three"=>3, "one_again"=>1}
2.2.2 :116 > value = 1
=> 1
2.2.2 :117 > hash.delete_if { |k,v| v == value }
=> {"two"=>2, "three"=>3}
2.2.2 :118 > hash
=> {"two"=>2, "three"=>3}
.compact => It is used to remove all nil values from the hash. Use compact! if you want to remove the nil values permanently else use simple compact.
2.2.2 :119 > hash = {"one"=>1, "two"=>2, "three"=>3, "nothing"=>nil, "no_value"=>nil}
=> {"one"=>1, "two"=>2, "three"=>3, "nothing"=>nil, "no_value"=>nil}
2.2.2 :120 > hash.compact
=> {"one"=>1, "two"=>2, "three"=>3}
Results based on Ruby 2.2.2.
If you want to use pure Ruby (no Rails), don't want to create extension methods (maybe you need this only in one or two places and don't want to pollute namespace with tons of methods) and don't want to edit hash in place (i.e., you're fan of functional programming like me), you can 'select':
>> x = {:a => 1, :b => 2, :c => 3}
=> {:a=>1, :b=>2, :c=>3}
>> x.select{|x| x != :a}
=> {:b=>2, :c=>3}
>> x.select{|x| ![:a, :b].include?(x)}
=> {:c=>3}
>> x
=> {:a=>1, :b=>2, :c=>3}
#in lib/core_extensions.rb
class Hash
#pass single or array of keys, which will be removed, returning the remaining hash
def remove!(*keys)
keys.each{|key| self.delete(key) }
self
end
#non-destructive version
def remove(*keys)
self.dup.remove!(*keys)
end
end
#in config/initializers/app_environment.rb (or anywhere in config/initializers)
require 'core_extensions'
I've set this up so that .remove returns a copy of the hash with the keys removed, while remove! modifies the hash itself. This is in keeping with ruby conventions. eg, from the console
>> hash = {:a => 1, :b => 2}
=> {:b=>2, :a=>1}
>> hash.remove(:a)
=> {:b=>2}
>> hash
=> {:b=>2, :a=>1}
>> hash.remove!(:a)
=> {:b=>2}
>> hash
=> {:b=>2}
>> hash.remove!(:a, :b)
=> {}
Hash#except (Ruby 3.0+)
Starting from Ruby 3.0, Hash#except is a build-in method.
As a result, there is no more need to depend on ActiveSupport or write monkey-patches in order to use it.
h = { a: 1, b: 2, c: 3 }
p h.except(:a) #=> {:b=>2, :c=>3}
Sources:
Hash#except from official Ruby docs.
Link to the PR.
Ruby 3.0 adds Hash#except and ENV.except.
You can use except! from the facets gem:
>> require 'facets' # or require 'facets/hash/except'
=> true
>> {:a => 1, :b => 2}.except(:a)
=> {:b=>2}
The original hash does not change.
EDIT: as Russel says, facets has some hidden issues and is not completely API-compatible with ActiveSupport. On the other side ActiveSupport is not as complete as facets. In the end, I'd use AS and let the edge cases in your code.
Instead of monkey patching or needlessly including large libraries, you can use refinements if you are using Ruby 2:
module HashExtensions
refine Hash do
def except!(*candidates)
candidates.each { |candidate| delete(candidate) }
self
end
def except(*candidates)
dup.remove!(candidates)
end
end
end
You can use this feature without affecting other parts of your program, or having to include large external libraries.
class FabulousCode
using HashExtensions
def incredible_stuff
delightful_hash.except(:not_fabulous_key)
end
end
in pure Ruby:
{:a => 1, :b => 2}.tap{|x| x.delete(:a)} # => {:b=>2}
See Ruby on Rails: Delete multiple hash keys
hash.delete_if{ |k,| keys_to_delete.include? k }
It's was great if delete return the delete pair of the hash.
I'm doing this:
hash = {a: 1, b: 2, c: 3}
{b: hash.delete(:b)} # => {:b=>2}
hash # => {:a=>1, :c=>3}
Try the except! method.
{:a => 1, :b => 2}.except!(:a) #=> {:b => 2}
This is a one line way to do it, but it's not very readable. Recommend using two lines instead.
use_remaining_hash_for_something(Proc.new { hash.delete(:key); hash }.call)
Multiple ways to delete Key in Hash.
you can use any Method from below
hash = {a: 1, b: 2, c: 3}
hash.except!(:a) # Will remove *a* and return HASH
hash # Output :- {b: 2, c: 3}
hash = {a: 1, b: 2, c: 3}
hash.delete(:a) # will remove *a* and return 1 if *a* not present than return nil
So many ways is there, you can look on Ruby doc of Hash here.
Thank you
This would also work: hash[hey] = nil
In PHP you can do:
print_r($var) or vardump($var)
which prints "human-readible" information about variable.
Is there equivalent functions / helpers for those in Ruby / Rails ?
In Rails templates you can do
<%= debug an_object %>
and it will do nice HTML PRE output.
Try using pp.
You will need to require it in scripts (or in irb if your .irbc doesn't already do this):
require 'pp'
Then you can 'PrettyPrint' an object thus:
pp object
Instead of requiring 'pp' and using pp, you can simply do
p object
Tested example
require 'pp'
class A
def initialize
#a = 'somevar'
#b = [1,2,3]
#c = {'var' => 'val'}
end
end
a = A.new
pp a # Gives -> #<A:0x2c6d048 #a="somevar", #b=[1, 2, 3], #c={"var"=>"val"}>
p a # Gives -> #<A:0x2c6d048 #a="somevar", #b=[1, 2, 3], #c={"var"=>"val"}>. No need to require 'pp'
There's the method inspect which helps. Sometimes calling the to_s method on an object will help (to_s returns a string representation of the object). You can also query methods, local_variables, class_variables, instance_variables, constants and global_variables.
p ['Hello',"G'day",'Bonjour','Hola'].inspect
# >> "[\"Hello\", \"G'day\", \"Bonjour\", \"Hola\"]"
p ['Hello',"G'day",'Bonjour','Hola'].to_s
# >> "HelloG'dayBonjourHola"
p Array.new.methods
# >> ["select", "[]=", "inspect", "compact"...]
monkey = 'baboon'
p local_variables
# >> ["monkey"]
class Something
def initialize
#x, #y = 'foo', 'bar'
##class_variable = 'gorilla'
end
end
p Something.class_variables
# >> ["##class_variable"]
s = Something.new
p s.instance_variables
# >> ["#x", "#y"]
p IO.constants
# >> ["TRUNC", "SEEK_END", "LOCK_SH"...]
p global_variables
# >> ["$-d", "$\"", "$$", "$<", "$_", "$-K"...]
I know this is an old post, but it is the first thing that Google pops up when searching for "Ruby equivalent of PHP print_r". I'm using Ruby in the command line mode, and there's really not a very good equivalent. "pp" is ok for fairly simple structures, but as soon as you start nesting hashes in arrays in hashes in more arrays, it turns into a jumble pretty fast. Since I haven't found a good emulation of print_r, I wrote one myself. It's good enough for my purposes, not overly complicated and I thought I'd share it to save other people some headache. Compare the output with the real PHP print_r
def print_r(inHash, *indent)
#indent = indent.join
if (inHash.class.to_s == "Hash") then
print "Hash\n#{#indent}(\n"
inHash.each { |key, value|
if (value.class.to_s =~ /Hash/) || (value.class.to_s =~ /Array/) then
print "#{#indent} [#{key}] => "
self.print_r(value, "#{#indent} ")
else
puts "#{#indent} [#{key}] => #{value}"
end
}
puts "#{#indent})\n"
elsif (inHash.class.to_s == "Array") then
print "Array\n#{#indent}(\n"
inHash.each_with_index { |value,index|
if (value.class.to_s == "Hash") || (value.class.to_s == "Array") then
print "#{#indent} [#{index}] => "
self.print_r(value, "#{#indent} ")
else
puts "#{#indent} [#{index}] => #{value}"
end
}
puts "#{#indent})\n"
end
# Pop last indent off
8.times {#indent.chop!}
end
Here's an example (made messy on purpose to show why the PHP print_r is so nice):
carTools = [ "Socket Set", "Combination Wrenches", "Oil Filter puller", "Brake Compressor" ]
houseTools =[ "Circular Saw", "Miter Saw", "Drill" ]
garageItems = Hash["Car1" => "Ford Mustang", "Car2" => "Honda Civic", "Bike1" => "IronHorse"]
garageItems["Tools"] = Hash["Car Tools" => carTools, "House Tools" => houseTools]
constructionSupplies = Hash["Plywood" => ["3/4\" T&G Plywood Sheets", "1/2\" Plywood Sheets"],
"Boards" => ["2x4s", "2x6s", "Engineered I-Joists"],
"Drywall" => ["4x8 1/2\" Sheetrock", "Mesh tape", "Paper tape", "Joint compount"]]
carParts = Hash["Mustang" => ["Clutch", "Transmission", "3.55 Ring & Pinion Gears", "Differential", "30# Injectors", "Pro-M 77mm MAF"]]
garageItems["Supplies"] = ["Oil", "WD40", constructionSupplies, carParts, "Brake Fluid"]
print_r(garageItems)
Output of print_r (actually comprehensible by a human):
Hash
(
[Car1] => Ford Mustang
[Car2] => Honda Civic
[Bike1] => IronHorse
[Tools] => Hash
(
[Car Tools] => Array
(
[0] => Socket Set
[1] => Combination Wrenches
[2] => Oil Filter puller
[3] => Brake Compressor
)
[House Tools] => Array
(
[0] => Circular Saw
[1] => Miter Saw
[2] => Drill
)
)
[Supplies] => Array
(
[0] => Oil
[1] => WD40
[2] => Hash
(
[Plywood] => Array
(
[0] => 3/4" T&G Plywood Sheets
[1] => 1/2" Plywood Sheets
)
[Boards] => Array
(
[0] => 2x4s
[1] => 2x6s
[2] => Engineered I-Joists
)
[Drywall] => Array
(
[0] => 4x8 1/2" Sheetrock
[1] => Mesh tape
[2] => Paper tape
[3] => Joint compount
)
)
[3] => Hash
(
[Mustang] => Array
(
[0] => Clutch
[1] => Transmission
[2] => 3.55 Ring & Pinion Gears
[3] => Differential
[4] => 30# Injectors
[5] => Pro-M 77mm MAF
)
)
[4] => Brake Fluid
)
)
Check out the guide for debugging rails:
http://guides.rubyonrails.com/debugging_rails_applications.html
hints:
script/console is great to try stuff in the context of your app
script/server --debugger to start the server with a debugger turned on, you can then use 'debug' in your code to break into an interactive shell
One approach I lean on a lot is this:
logger.debug "OBJECT: #{an_object.to_yaml}"
Easy to read, although it can get a little unwieldy for large objects.
Guess I'm a little late to this, but what about logger.info [debug|warning]? Use this from Controllers and Models. It will show up in your log files (development.log when in dev mode); and the above mentioned <%= debug("str: " + str) %> for views.
These aren't exact answers to your questions but you can also use script/console to load your rails app in to an interactive session.
Lastly, you can place debugger in a line of your rails application and the browser will "hang" when your app executes this line and you'll be able to be in a debug session from the exact line your placed your debugger in the source code.