Asp Forum - How to retrive first 10 items from hash in ruby?

Vikas Gholap

2/13/2009 11:04:00 AM

Hello All, I am new to programming, i have little problem with hash.

I want to retrieve first 10 items(key value pairs) from given hash{}

hashTable = {"a" => 1, "b" => 5, "c" => 2, "d" => 6, "e" => 4, "f" => 7,
"g" => 9, "h" => 5, "i" => 1, "j" => 8, "k" => 9, "l" => 3, "m" => 7,
"n" => 10, "o" => 12}

#sort hashTable on value by descending order
hashTable.sort {|a,b| -1*(a[1]<=>b[1])}

#now I want 10 items from sorted hashTable

I wrote some thing like
---------------------------------
hashTable.each do |key,value|
puts"Key: #{key} ==> #{value}"
# I want only first 10
end
------------------------------------
it prints all elements but i want only 10 items. please help.

Thanks,
Vikas
--
Posted via http://www.ruby-....

10 Answers

Dave Baldwin

2/13/2009 12:08:00 PM

On 13 Feb 2009, at 11:04, Vikas Gholap wrote:

> Hello All, I am new to programming, i have little problem with hash.
>
> I want to retrieve first 10 items(key value pairs) from given hash{}
>
> hashTable = {"a" => 1, "b" => 5, "c" => 2, "d" => 6, "e" => 4, "f"
> => 7,
> "g" => 9, "h" => 5, "i" => 1, "j" => 8, "k" => 9, "l" => 3, "m" => 7,
> "n" => 10, "o" => 12}
>
> #sort hashTable on value by descending order
> hashTable.sort {|a,b| -1*(a[1]<=>b[1])}

You need to save the results.
ary = hashTable.sort {|a,b| -1*(a[1]<=>b[1])}

ary is an array of key value pairs stored in an array, i.e. [['o' =>
12], ['n' => 11], ...]

ary[0, 10] will return an array of the first 10 entries

To print out the first 10 entries:

ary[0, 10].each {|e| puts "Key: #{e[0} ==> #{[e[1]}"

Dave
>
>
> #now I want 10 items from sorted hashTable
>
> I wrote some thing like
> ---------------------------------
> hashTable.each do |key,value|
> puts"Key: #{key} ==> #{value}"
> # I want only first 10
> end
> ------------------------------------
> it prints all elements but i want only 10 items. please help.
>
> Thanks,
> Vikas
> --
> Posted via http://www.ruby-....
>

Bil Kleb

2/13/2009 12:21:00 PM

Dave Baldwin wrote:
>
> ary[0, 10] will return an array of the first 10 entries

Or, alternatively,

ary.first(10)

Regards,
--
Bil Kleb
http://fun3d.lar...
http://twitter.co...

Jakub Pavlík jn.

2/13/2009 12:31:00 PM

> Hello All, I am new to programming, i have little problem with hash.
>
> I want to retrieve first 10 items(key value pairs) from given hash{}
>
> hashTable = {"a" => 1, "b" => 5, "c" => 2, "d" => 6, "e" => 4, "f" => 7,
> "g" => 9, "h" => 5, "i" => 1, "j" => 8, "k" => 9, "l" => 3, "m" => 7,
> "n" => 10, "o" => 12}
>
> #sort hashTable on value by descending order
> hashTable.sort {|a,b| -1*(a[1]<=>b[1])}
>
> #now I want 10 items from sorted hashTable
>
> I wrote some thing like
> ---------------------------------
> hashTable.each do |key,value|
> puts"Key: #{key} ==> #{value}"
> # I want only first 10
> end
> ------------------------------------
> it prints all elements but i want only 10 items. please help.
>
> Thanks,
> Vikas
> --
> Posted via http://www.ruby-....

i = 0
hashTable.each_pair {|key,value|
break if i >= 10
puts "Key: ..."
i+=1
}

Is this what you need?

--
"Configure complete, now type 'make' and PRAY."

(configure script of zsnes - www.zsnes.com)

Bertram Scharpf

2/13/2009 12:52:00 PM

Hi,

Am Freitag, 13. Feb 2009, 21:08:19 +0900 schrieb Dave Baldwin:
>
> On 13 Feb 2009, at 11:04, Vikas Gholap wrote:
>
>> I want to retrieve first 10 items(key value pairs) from given hash{}
>>
>> hashTable.sort {|a,b| -1*(a[1]<=>b[1])}
>
> You need to save the results.
> ary = hashTable.sort {|a,b| -1*(a[1]<=>b[1])}
>
> ary[0, 10] will return an array of the first 10 entries
>
> ary[0, 10].each {|e| puts "Key: #{e[0} ==> #{[e[1]}"

As ary is only of temporary use, you don't need to create another
array ary[0,10]. I suggest:

10.times { puts "Key: %s ==> %s" % e.shift }
e.clear # optional

Bertram

--
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-...

David A. Black

2/13/2009 1:03:00 PM

Hi --

On Fri, 13 Feb 2009, Bertram Scharpf wrote:

> Hi,
>
> Am Freitag, 13. Feb 2009, 21:08:19 +0900 schrieb Dave Baldwin:
>>
>> On 13 Feb 2009, at 11:04, Vikas Gholap wrote:
>>
>>> I want to retrieve first 10 items(key value pairs) from given hash{}
>>>
>>> hashTable.sort {|a,b| -1*(a[1]<=>b[1])}
>>
>> You need to save the results.
>> ary = hashTable.sort {|a,b| -1*(a[1]<=>b[1])}
>>
>> ary[0, 10] will return an array of the first 10 entries
>>
>> ary[0, 10].each {|e| puts "Key: #{e[0} ==> #{[e[1]}"
>
> As ary is only of temporary use, you don't need to create another
> array ary[0,10]. I suggest:
>
> 10.times { puts "Key: %s ==> %s" % e.shift }

Do you mean ary.shift?

> e.clear # optional

You can also save on shifts like this:

10.times {|i| # do something with ary[i] }

David

--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.r...
Coming in 2009: The Well-Grounded Rubyist (http://manning....)

http://www.wis... => Independent, social wishlist management!

Bertram Scharpf

2/13/2009 1:26:00 PM

Hi,

Am Freitag, 13. Feb 2009, 22:02:31 +0900 schrieb David A. Black:
> On Fri, 13 Feb 2009, Bertram Scharpf wrote:
>> Am Freitag, 13. Feb 2009, 21:08:19 +0900 schrieb Dave Baldwin:
>>> On 13 Feb 2009, at 11:04, Vikas Gholap wrote:
>>>
>>>> I want to retrieve first 10 items(key value pairs) from given hash{}
>>>>
>>> ary = hashTable.sort {|a,b| -1*(a[1]<=>b[1])}
>>>
>> As ary is only of temporary use, you don't need to create another
>> array ary[0,10]. I suggest:
>>
>> 10.times { puts "Key: %s ==> %s" % e.shift }
>
> Do you mean ary.shift?

Arrgh. Of course.

The code may still be improved: Omit the multiplication by -1 in
the sort block.

ary = hashTable.sort { |a,b| a[1]<=>b[1] }
10.times { puts "Key: %s ==> %s" % ary.pop }

Bertram

--
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-...

David A. Black

2/13/2009 2:29:00 PM

Hi --

On Fri, 13 Feb 2009, Bertram Scharpf wrote:

> Hi,
>
> Am Freitag, 13. Feb 2009, 22:02:31 +0900 schrieb David A. Black:
>> On Fri, 13 Feb 2009, Bertram Scharpf wrote:
>>> Am Freitag, 13. Feb 2009, 21:08:19 +0900 schrieb Dave Baldwin:
>>>> On 13 Feb 2009, at 11:04, Vikas Gholap wrote:
>>>>
>>>>> I want to retrieve first 10 items(key value pairs) from given hash{}
>>>>>
>>>> ary = hashTable.sort {|a,b| -1*(a[1]<=>b[1])}
>>>>
>>> As ary is only of temporary use, you don't need to create another
>>> array ary[0,10]. I suggest:
>>>
>>> 10.times { puts "Key: %s ==> %s" % e.shift }
>>
>> Do you mean ary.shift?
>
> Arrgh. Of course.
>
> The code may still be improved: Omit the multiplication by -1 in
> the sort block.
>
> ary = hashTable.sort { |a,b| a[1]<=>b[1] }
> 10.times { puts "Key: %s ==> %s" % ary.pop }

I'd still rather walk through the array than have to coordinate the
sort operation and a destructive array operation.

ary = hash_table.sort {|a,b| b[1] <=> a[1] }
# or sort_by {|a| -a[1]}
10.times {|i| # ary[i] ... }

David

--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.r...
Coming in 2009: The Well-Grounded Rubyist (http://manning....)

http://www.wis... => Independent, social wishlist management!

Robert Klemme

2/13/2009 3:18:00 PM

2009/2/13 Bertram Scharpf <lists@bertram-scharpf.de>:
> Hi,
>
> Am Freitag, 13. Feb 2009, 22:02:31 +0900 schrieb David A. Black:
>> On Fri, 13 Feb 2009, Bertram Scharpf wrote:
>>> Am Freitag, 13. Feb 2009, 21:08:19 +0900 schrieb Dave Baldwin:
>>>> On 13 Feb 2009, at 11:04, Vikas Gholap wrote:
>>>>
>>>>> I want to retrieve first 10 items(key value pairs) from given hash{}
>>>>>
>>>> ary = hashTable.sort {|a,b| -1*(a[1]<=>b[1])}
>>>>
>>> As ary is only of temporary use, you don't need to create another
>>> array ary[0,10]. I suggest:
>>>
>>> 10.times { puts "Key: %s ==> %s" % e.shift }
>>
>> Do you mean ary.shift?
>
> Arrgh. Of course.
>
> The code may still be improved: Omit the multiplication by -1 in
> the sort block.
>
> ary = hashTable.sort { |a,b| a[1]<=>b[1] }
> 10.times { puts "Key: %s ==> %s" % ary.pop }

Did we have these already?

p hash_table.sort_by {|k,v| -v}.first(10)
p hash_table.sort_by {|k,v| v}.last(10).reverse

Cheers

robert

--
remember.guy do |as, often| as.you_can - without end

David A. Black

2/13/2009 3:21:00 PM

Hi --

On Sat, 14 Feb 2009, Robert Klemme wrote:

> 2009/2/13 Bertram Scharpf <lists@bertram-scharpf.de>:
>> Hi,
>>
>> Am Freitag, 13. Feb 2009, 22:02:31 +0900 schrieb David A. Black:
>>> On Fri, 13 Feb 2009, Bertram Scharpf wrote:
>>>> Am Freitag, 13. Feb 2009, 21:08:19 +0900 schrieb Dave Baldwin:
>>>>> On 13 Feb 2009, at 11:04, Vikas Gholap wrote:
>>>>>
>>>>>> I want to retrieve first 10 items(key value pairs) from given hash{}
>>>>>>
>>>>> ary = hashTable.sort {|a,b| -1*(a[1]<=>b[1])}
>>>>>
>>>> As ary is only of temporary use, you don't need to create another
>>>> array ary[0,10]. I suggest:
>>>>
>>>> 10.times { puts "Key: %s ==> %s" % e.shift }
>>>
>>> Do you mean ary.shift?
>>
>> Arrgh. Of course.
>>
>> The code may still be improved: Omit the multiplication by -1 in
>> the sort block.
>>
>> ary = hashTable.sort { |a,b| a[1]<=>b[1] }
>> 10.times { puts "Key: %s ==> %s" % ary.pop }
>
> Did we have these already?
>
> p hash_table.sort_by {|k,v| -v}.first(10)
> p hash_table.sort_by {|k,v| v}.last(10).reverse

I think the original split between the sort and the puts was because
the main question was about sort, and the puts was just to examine the
results.

David

--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.r...
Coming in 2009: The Well-Grounded Rubyist (http://manning....)

http://www.wis... => Independent, social wishlist management!

Bertram Scharpf

2/13/2009 4:38:00 PM

Hi,

Am Freitag, 13. Feb 2009, 23:29:05 +0900 schrieb David A. Black:
> On Fri, 13 Feb 2009, Bertram Scharpf wrote:
>>
>> ary = hashTable.sort { |a,b| a[1]<=>b[1] }
>> 10.times { puts "Key: %s ==> %s" % ary.pop }
>
> I'd still rather walk through the array than have to coordinate the
> sort operation and a destructive array operation.
>
> ary = hash_table.sort {|a,b| b[1] <=> a[1] }
> # or sort_by {|a| -a[1]}
> 10.times {|i| # ary[i] ... }

By the way: This is starting to make fun. I don't know how the
internal sort mechanism works, but maybe something like this here
would be faster?

a = Array.new 200 do rand 0x1000 end
h = []
a.each { |x|
if h.length < 10 or x > h.first then
h.push x
h.sort!
h.shift if h.length > 10
end
}

Bertram

--
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-...

comp.lang.ruby

How to retrive first 10 items from hash in ruby?

Vikas Gholap

Dave Baldwin

Bil Kleb

Jakub Pavlík jn.

Bertram Scharpf

David A. Black

Bertram Scharpf

David A. Black

Robert Klemme

David A. Black

Bertram Scharpf

x Login to ForumsZone