How to make an array of hashes to a single array with all th

kazaam · August 29, 2007, 8:41pm

Take a look at this,
puts myvalue.inspect
shows this here:

[{:url=>“http://www.ruby-lang.org/”},
{:url=>“http://www.ruby-lang.org/en/20020101.html”},
{:url=>“http://en.wikipedia.org/wiki/Ruby_programming_language”},
{:url=>“Ruby - Wikipedia”},
{:url=>“http://www.rubyonrails.org/”},
{:url=>“Kaiser Chiefs - Ruby - YouTube”},
{:url=>“http://www.rubycentral.org/”},
{:url=>“Ruby | zenspider.com | by ryan davis”},
{:url=>“http://www.rubycentral.com/book/”},
{:url=>“http://poignantguide.net/”}]

That’s an array of hashes or? But how to get this to an array of the
values of these hashes? Like my_new_array ==
[“http://www.ruby-lang.org/",“http://www.ruby-lang.org/en/20020101.html”,"http://en.wikipedia.org/wiki/Ruby_programming_language”,…].

myvalue.each {|arr| puts arr.values }
gives me:

http://www.ruby-lang.org/
http://www.ruby-lang.org/en/20020101.html

http://www.rubycentral.com/book/
http://poignantguide.net/

what’s correct! But I can’t save it to an array. Why? I tried
myvalue.each {|arr| @my_new_array << arr.values }
puts @my_new_array
But I just get nil ? I can’t make an array out of this.

kazaam · August 29, 2007, 8:51pm

On Aug 29, 12:39 pm, kazaam [email protected] wrote:

That’s an array of hashes or? But how to get this to an array of the values of these hashes?

Depending on what you want, try either:
my_array.map{ |h| h[:url] }
or
my_array.map{ |h| h.values }.flatten

kazaam · August 29, 2007, 9:55pm

On Aug 29, 8:45 pm, Phrogz [email protected] wrote:

On Aug 29, 12:39 pm, kazaam [email protected] wrote:

That’s an array of hashes or? But how to get this to an array of the values of these hashes?

Depending on what you want, try either:
my_array.map{ |h| h[:url] }
or
my_array.map{ |h| h.values }.flatten

The beauty is that you can do the same stuff in so many different
ways

data = [{:url=>“http://www.ruby-lang.org/”}, {:url=>“http://www.ruby-
Lang.org”}, {:url=>“Wikipedia, the free encyclopedia
Ruby_programming_language”}, {:url=>“Wikipedia, the free encyclopedia
Ruby”}, {:url=>“http://www.rubyonrails.org/”}, {:url=>“http://
Kaiser Chiefs - Ruby - YouTube”}, {:url=>“http://
www.rubycentral.org/”}, {:url=>“http://www.zenspider.com/Languages/
Ruby/QuickRef.html”}, {:url=>“http://www.rubycentral.com/book/”},
{:url=>“http://poignantguide.net/”}]

a = []

data.collect do |item|
item.each_value { |value| a << value }
end

kazaam · August 30, 2007, 12:18am

myvalue.to_s[3…-1].split(‘url’)

Regards
Florian

kazaam · August 30, 2007, 10:16am

thanks guys! dimas solution showed me my error

myvalue.each {|arr| @my_new_array << arr.values }
puts @my_new_array

is working if I initialize @my_new_array = [] before like dima did with
a = [] but two questions:

Why is a local variable my_new_array not working but just @ instance or
$ global variables and why do I have
initialize this varriable? I think you don’t need this in ruby? But
without initialisation it just shows nil?

greets

kazaam · August 29, 2007, 10:51pm

On Aug 29, 2:53 pm, dima [email protected] wrote:

The beauty is that you can do the same stuff in so many different
ways

I’ll offer up an inject solution for this one:

my_new_array = myvalue.inject([]) {|arr, h| arr + h.values}

Jeremy

kazaam · August 30, 2007, 4:29pm

2007/8/29, [email protected] [email protected]:

On Aug 29, 2:53 pm, dima [email protected] wrote:

The beauty is that you can do the same stuff in so many different
ways

I’ll offer up an inject solution for this one:

my_new_array = myvalue.inject([]) {|arr, h| arr + h.values}

That’s already pretty good (you used #inject ;-)) but this one is
slightly more efficient:

my_new_array = myvalue.inject([]) {|arr, h| arr.concat h.values}

Kind regards

robert

kazaam · August 30, 2007, 4:23pm

On 8/30/07, kazaam [email protected] wrote:

thanks guys! dimas solution showed me my error
    myvalue.each {|arr|  @my_new_array << arr.values }
    puts @my_new_array
is working if I initialize @my_new_array = [] before like dima did with a = [] but two questions:

Why is a local variable my_new_array not working but just @ instance or $ global variables and why do I have
initialize this varriable? I think you don’t need this in ruby? But without initialisation it just shows nil?

It’s about scope. I’m sure the veterans here can give you a thorough
explanation, (and please pipe in here, because I don’t want to spread
disinformation), but basically the block tries to retain its own scope
as best it can (from what I understand). So, new variables that are
not “swallowed” from the scope outside of the block need to be
initialized, and those initialized within the block don’t get outside
of the block (what happens in Vegas stays in Vegas, blah blah).

Simple example…

irb(main):001:0> a = 1,2,3,4
=> [1, 2, 3, 4]
irb(main):002:0> a.each { |i| b = i } #nothing happens here outside of
the block for b
=> [1, 2, 3, 4]
irb(main):003:0> b
NameError: undefined local variable or method `b’ for main:object

Here’s one that will make you think a little that is somewhat OT, but
demonstrates namespace danger…

irb(main):001:0> a = 1,2,3,4
=> [1, 2, 3, 4]
irb(main):002:0> a.inject{ |s, a| s + a }
=> 10
irb(main):003:0> a
=> 4

The a is not the accumulator, but it has changed even though the
method doesn’t have a ! following it. These are the small
idiosyncrasies that we have to be aware of with namespace and scope.

I may not be understanding your question, though.

kazaam [email protected]

Todd

kazaam · August 30, 2007, 4:48pm

On 8/30/07, Robert K. [email protected] wrote:

2007/8/29, [email protected] [email protected]:

On Aug 29, 2:53 pm, dima [email protected] wrote:

my_new_array = myvalue.inject([]) {|arr, h| arr + h.values}

That’s already pretty good (you used #inject ;-)) but this one is
slightly more efficient:

my_new_array = myvalue.inject([]) {|arr, h| arr.concat h.values}

Nice. You beat me to it. One of these days, though, I’ll read all
the Ruby source and exact vengeance upon you guys

For a short repeat of the record for the nubies, #concat supposedly
doesn’t create new objects, and thus is more “efficient”.

Todd

kazaam · August 30, 2007, 11:10pm

On 30.08.2007 16:47, Todd B. wrote:

Nice. You beat me to it. One of these days, though, I’ll read all
the Ruby source and exact vengeance upon you guys

gulp

For a short repeat of the record for the nubies, #concat supposedly
doesn’t create new objects, and thus is more “efficient”.

To be fair I’d have to say that often intuition errs about what is fast
and what is wrong in Ruby. Sometimes algorithms that are supposedly
faster (for example because a collection is iterated only once vs.
several times) are actually slower than other variants - at least for
the size of collections that programs typically deal with. (In this
case if’s of course better to save all those superfluous intermediate
arrays. :-))

Kind regards

robert

kazaam · August 31, 2007, 2:11am

On 8/30/07, Robert K. [email protected] wrote:

Nice. You beat me to it. One of these days, though, I’ll read all
the Ruby source and exact vengeance upon you guys

gulp

Hopefully, everybody took that in good stride

To be fair I’d have to say that often intuition errs about what is fast
and what is wrong in Ruby. Sometimes algorithms that are supposedly
faster (for example because a collection is iterated only once vs.
several times) are actually slower than other variants - at least for
the size of collections that programs typically deal with. (In this
case if’s of course better to save all those superfluous intermediate
arrays. :-))

Yes. I’ve noticed a good deal of discussion along these lines in this
group, and it fascinates me (thus the comment about the source code
:).

Also, there are good lessons about software engineering in general on
this list (a group comprised of very smart people that sometimes I
feel as if I do not really belong), like: being careful about
emphasizing efficiency in the design phase, and then grabbing the
program by the proverbial balls later on

Kind regards
    robert

Learning a ton of things every day,

Thanks,

Todd

kazaam · September 13, 2007, 3:31pm

On 30.08.2007 16:22, Todd B. wrote:

of the block (what happens in Vegas stays in Vegas, blah blah).

The a is not the accumulator, but it has changed even though the
method doesn’t have a ! following it. These are the small
idiosyncrasies that we have to be aware of with namespace and scope.

Is there something I can do to avoid name clashes for block parameters?

f.e. standard:

x=“external”
a= 1,2,3,4

a.each {|x| puts x*x}
puts x # => 4

vs. clash avoision (note the exclamation mark):

x=“external”
a= 1,2,3,4

a.each {|!x| puts x*x}
puts x # => “external”

Matthias

kazaam · August 31, 2007, 8:01am

On 31.08.2007 02:09, Todd B. wrote:

Nice. You beat me to it. One of these days, though, I’ll read all
the Ruby source and exact vengeance upon you guys
gulp

Hopefully, everybody took that in good stride

I can speak for myself only but I did.

:).

Also, there are good lessons about software engineering in general on
this list (a group comprised of very smart people that sometimes I
feel as if I do not really belong), like: being careful about
emphasizing efficiency in the design phase, and then grabbing the
program by the proverbial balls later on

If that feeling haunts you again simply remember that all smart
people started out as dumb as everyone else. Also, as long as one
actually feels stupid one won’t forget that one does not know the answer
to everything - it helps me keeping things in perspective.

Much of this smartness is just a matter of experience, namely having run
into the same traps and made the same mistakes that others haven’t hit
so far.

And: You are absolutely right: this is a great community and it’s good
that someone states it from time to time.

Learning a ton of things every day,

Definitively!

Kind regards

robert