# Group by unique entries of a hash

**URL:** <https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592>\
**Category:** ruby-talk\
**Created:** [29 September 2009 11:43 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592 "2009-09-29T11:43:40Z")\
**Posts on this page:** 15\
**Page:** 1

<div class="post-metadata">

**Author:** ![Ne\_Scripter](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Ne\_Scripter](https://rubytalk.org/u/Ne_Scripter)\
**Post date:** [29 September 2009 11:43 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/1 "2009-09-29T11:43:40Z")

</div>

I have two data sets loaded into a hash to give the following output

"2efa4ba470", "00000005"  
"2efa4ba470", "00000004"  
"02adecfd5c", "00000002"  
"c0784b5de101", "00000006"  
"68c4bf10539", "00000003"  
"c0784b5de101", "00000001"

My code to get this is as follows:

&nbsp;&nbsp;source= "C:\\dummyFile.txt"  
&nbsp;&nbsp;hashMapping = Hash.new  
&nbsp;&nbsp;ocrIDMapping = Hash.new

&nbsp;&nbsp;IO.foreach(source.to\_s) do |data|  
&nbsp;&nbsp;&nbsp;&nbsp;fields = data.split(",")  
&nbsp;&nbsp;&nbsp;&nbsp;hash = fields[0]  
&nbsp;&nbsp;&nbsp;&nbsp;ocrID = fields[1]  
&nbsp;&nbsp;&nbsp;&nbsp;hashMapping[ocrID] = hash  
&nbsp;&nbsp;end

&nbsp;&nbsp;hashMapping.sort{|a,b| a[1]\<=\>b[1]}.each { |elem|

&nbsp;&nbsp;puts "#{elem[1]}, #{elem[0]}"}

I would like to alter my output to group my the first value to give an  
output like this:

"2efa4ba470", "00000005", "00000004"  
"02adecfd5c", "00000002"  
"c0784b5de101", "00000006", "00000001"  
"68c4bf10539", "00000003"

As you can see now only unique values are shown in the first field  
however a list of the corresponding second field is formed, grouping the  
results. Something like this I could do in SQL however I have never come  
across it in Ruby so does anyone have any pointers?

Many thanks

> **···**
>
> --  
> Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).

---

<div class="post-metadata">

**Author:** ![Paul\_Smith1](https://avatars.discourse-cdn.com/v4/letter/p/5daacb/32.png) [@Paul\_Smith1](https://rubytalk.org/u/Paul_Smith1)\
**Post date:** [29 September 2009 11:55 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/2 "2009-09-29T11:55:44Z")

</div>

> I have two data sets loaded into a hash to give the following output
> 
> "2efa4ba470", "00000005"  
> "2efa4ba470", "00000004"  
> "02adecfd5c", "00000002"  
> "c0784b5de101", "00000006"  
> "68c4bf10539", "00000003"  
> "c0784b5de101", "00000001"
> 
> My code to get this is as follows:
> 
> source= "C:\\dummyFile.txt"  
> hashMapping = Hash.new  
> ocrIDMapping = Hash.new
> 
> IO.foreach(source.to\_s) do |data|  
> fields = data.split(",")  
> hash = fields[0]  
> ocrID = fields[1]  
> hashMapping[ocrID] = hash  
> end
> 
> hashMapping.sort{|a,b| a[1]\<=\>b[1]}.each { |elem|
> 
> puts "#{elem[1]}, #{elem[0]}"}
> 
> I would like to alter my output to group my the first value to give an  
> output like this:
> 
> "2efa4ba470", "00000005", "00000004"  
> "02adecfd5c", "00000002"  
> "c0784b5de101", "00000006", "00000001"  
> "68c4bf10539", "00000003"
> 
> As you can see now only unique values are shown in the first field  
> however a list of the corresponding second field is formed, grouping the  
> results. Something like this I could do in SQL however I have never come  
> across it in Ruby so does anyone have any pointers?

You want a hash where the key is the element you want to group on, and  
the 'item' is an array of all items with the shared key. A bit like  
(untested):

hashMapping = {}

IO.foreach(source.to\_s) do |data|  
&nbsp;&nbsp;&nbsp;fields = data.split(",")  
&nbsp;&nbsp;&nbsp;hash = fields[0]  
&nbsp;&nbsp;&nbsp;ocrID = fields[1]

&nbsp;&nbsp;&nbsp;hashMapping[ocrID] ||= #If hashMapping has never seen this key  
before, make an empty array

&nbsp;&nbsp;&nbsp;hashMapping[ocrID] \<\< hash #Add the new element to the array for this key

end

> **···**
>
> On Tue, Sep 29, 2009 at 12:43 PM, Ne Scripter \<stuart.clarke@northumbria.ac.uk\> wrote:
> 
> > Many thanks  
> > --  
> > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).
> 
> --  
> Paul Smith  
> [http://www.nomadicfun.co.uk](http://www.nomadicfun.co.uk)
> 
> paul@pollyandpaul.co.uk

---

<div class="post-metadata">

**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\
**Post date:** [29 September 2009 13:38 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/3 "2009-09-29T13:38:37Z")

</div>

It is slightly more efficient to do it in one step:

(hashMapping[ocrID] ||= ) \<\< hash

Even nicer

hashMapping = Hash.new {|h,k| h[k] = }  
...  
hashMapping[ocrID] \<\< hash

Kind regards

robert

> **···**
>
> 2009/9/29 Paul Smith \<paul@pollyandpaul.co.uk\>:
> 
> > On Tue, Sep 29, 2009 at 12:43 PM, Ne Scripter \> \<stuart.clarke@northumbria.ac.uk\> wrote:
> > 
> > > I have two data sets loaded into a hash to give the following output
> > > 
> > > "2efa4ba470", "00000005"  
> > > "2efa4ba470", "00000004"  
> > > "02adecfd5c", "00000002"  
> > > "c0784b5de101", "00000006"  
> > > "68c4bf10539", "00000003"  
> > > "c0784b5de101", "00000001"
> > > 
> > > My code to get this is as follows:
> > > 
> > > source= "C:\\dummyFile.txt"  
> > > hashMapping = Hash.new  
> > > ocrIDMapping = Hash.new
> > > 
> > > IO.foreach(source.to\_s) do |data|  
> > > fields = data.split(",")  
> > > hash = fields[0]  
> > > ocrID = fields[1]  
> > > hashMapping[ocrID] = hash  
> > > end
> > > 
> > > hashMapping.sort{|a,b| a[1]\<=\>b[1]}.each { |elem|
> > > 
> > > puts "#{elem[1]}, #{elem[0]}"}
> > > 
> > > I would like to alter my output to group my the first value to give an  
> > > output like this:
> > > 
> > > "2efa4ba470", "00000005", "00000004"  
> > > "02adecfd5c", "00000002"  
> > > "c0784b5de101", "00000006", "00000001"  
> > > "68c4bf10539", "00000003"
> > > 
> > > As you can see now only unique values are shown in the first field  
> > > however a list of the corresponding second field is formed, grouping the  
> > > results. Something like this I could do in SQL however I have never come  
> > > across it in Ruby so does anyone have any pointers?
> > 
> > You want a hash where the key is the element you want to group on, and  
> > the 'item' is an array of all items with the shared key. A bit like  
> > (untested):
> > 
> > hashMapping = {}
> > 
> > IO.foreach(source.to\_s) do |data|  
> > fields = data.split(",")  
> > hash = fields[0]  
> > ocrID = fields[1]
> > 
> > hashMapping[ocrID] ||= #If hashMapping has never seen this key  
> > before, make an empty array
> > 
> > hashMapping[ocrID] \<\< hash #Add the new element to the array for this key
> > 
> > end
> 
> --  
> remember.guy do |as, often| as.you\_can - without end  
> [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/)

---

<div class="post-metadata">

**Author:** ![Ne\_Scripter](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Ne\_Scripter](https://rubytalk.org/u/Ne_Scripter)\
**Post date:** [29 September 2009 15:28 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/4 "2009-09-29T15:28:42Z")

</div>

Ah yes, that makes perfect sense.

Thanks

Paul Smith wrote:

> **···**
>
> > You want a hash where the key is the element you want to group on, and  
> > the 'item' is an array of all items with the shared key. A bit like  
> > (untested):
> > 
> > hashMapping = {}
> > 
> > IO.foreach(source.to\_s) do |data|  
> > &nbsp;&nbsp;&nbsp;fields = data.split(",")  
> > &nbsp;&nbsp;&nbsp;hash = fields[0]  
> > &nbsp;&nbsp;&nbsp;ocrID = fields[1]
> > 
> > &nbsp;&nbsp;&nbsp;hashMapping[ocrID] ||= #If hashMapping has never seen this key  
> > before, make an empty array
> > 
> > &nbsp;&nbsp;&nbsp;hashMapping[ocrID] \<\< hash #Add the new element to the array for this  
> > key
> > 
> > end
> > 
> > > Many thanks  
> > > --  
> > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).
> > 
> > --  
> > Paul Smith  
> > [http://www.nomadicfun.co.uk](http://www.nomadicfun.co.uk)
> > 
> > paul@pollyandpaul.co.uk
> 
> --  
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).

---

<div class="post-metadata">

**Author:** ![Simon\_Krahnke](https://avatars.discourse-cdn.com/v4/letter/s/b782af/32.png) [@Simon\_Krahnke](https://rubytalk.org/u/Simon_Krahnke)\
**Post date:** [30 September 2009 16:05 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/5 "2009-09-30T16:05:09Z")

</div>

\* Paul Smith \<paul@pollyandpaul.co.uk\> (2009-09-29) schrieb:

> > fields = data.split(",")  
> > hash = fields[0]  
> > ocrID = fields[1]

BTW, you could write this as:

hash, ocrID = \*data.split(",")

or

hash, ocrID, \*ignored = \*data.split(",")

if you want to ignore everything behind a second comma, or

hash, ocrID = \*data.split(",", 2)

if you want to include a second comma and everything behind it into the  
ocrID string.

mfg, simon .... which color is the green bill? blue!

---

<div class="post-metadata">

**Author:** ![Paul\_Smith1](https://avatars.discourse-cdn.com/v4/letter/p/5daacb/32.png) [@Paul\_Smith1](https://rubytalk.org/u/Paul_Smith1)\
**Post date:** [29 September 2009 14:22 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/6 "2009-09-29T14:22:54Z")

</div>

> > > I have two data sets loaded into a hash to give the following output
> > > 
> > > "2efa4ba470", "00000005"  
> > > "2efa4ba470", "00000004"  
> > > "02adecfd5c", "00000002"  
> > > "c0784b5de101", "00000006"  
> > > "68c4bf10539", "00000003"  
> > > "c0784b5de101", "00000001"
> > > 
> > > My code to get this is as follows:
> > > 
> > > source= "C:\\dummyFile.txt"  
> > > hashMapping = Hash.new  
> > > ocrIDMapping = Hash.new
> > > 
> > > IO.foreach(source.to\_s) do |data|  
> > > fields = data.split(",")  
> > > hash = fields[0]  
> > > ocrID = fields[1]  
> > > hashMapping[ocrID] = hash  
> > > end
> > > 
> > > hashMapping.sort{|a,b| a[1]\<=\>b[1]}.each { |elem|
> > > 
> > > puts "#{elem[1]}, #{elem[0]}"}
> > > 
> > > I would like to alter my output to group my the first value to give an  
> > > output like this:
> > > 
> > > "2efa4ba470", "00000005", "00000004"  
> > > "02adecfd5c", "00000002"  
> > > "c0784b5de101", "00000006", "00000001"  
> > > "68c4bf10539", "00000003"
> > > 
> > > As you can see now only unique values are shown in the first field  
> > > however a list of the corresponding second field is formed, grouping the  
> > > results. Something like this I could do in SQL however I have never come  
> > > across it in Ruby so does anyone have any pointers?
> > 
> > You want a hash where the key is the element you want to group on, and  
> > the 'item' is an array of all items with the shared key. A bit like  
> > (untested):
> > 
> > hashMapping = {}
> > 
> > IO.foreach(source.to\_s) do |data|  
> > fields = data.split(",")  
> > hash = fields[0]  
> > ocrID = fields[1]
> > 
> > hashMapping[ocrID] ||= #If hashMapping has never seen this key  
> > before, make an empty array
> > 
> > hashMapping[ocrID] \<\< hash #Add the new element to the array for this key
> > 
> > end
> 
> It is slightly more efficient to do it in one step:
> 
> (hashMapping[ocrID] ||= ) \<\< hash
> 
> Even nicer
> 
> hashMapping = Hash.new {|h,k| h[k] = }

Is this defining a default element for the hash? I had a vague  
recollection you could do this but completely forgot how.

I'd also rename the 'hash' variable to 'key' or something, I think  
it's less confusing. Then Your hashMapping can either be given the  
name 'hash', because that's what it is, or a name that's actually  
useful for describing what the mystical contents of the hash are.

> **···**
>
> On Tue, Sep 29, 2009 at 2:38 PM, Robert Klemme \<shortcutter@googlemail.com\> wrote:
> 
> > 2009/9/29 Paul Smith \<paul@pollyandpaul.co.uk\>:
> > 
> > > On Tue, Sep 29, 2009 at 12:43 PM, Ne Scripter \>\> \<stuart.clarke@northumbria.ac.uk\> wrote:
> 
> > ...  
> > hashMapping[ocrID] \<\< hash
> > 
> > Kind regards
> > 
> > robert
> > 
> > --  
> > remember.guy do |as, often| as.you\_can - without end  
> > [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/)
> 
> --  
> Paul Smith  
> [http://www.nomadicfun.co.uk](http://www.nomadicfun.co.uk)
> 
> paul@pollyandpaul.co.uk

---

<div class="post-metadata">

**Author:** ![Ne\_Scripter](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Ne\_Scripter](https://rubytalk.org/u/Ne_Scripter)\
**Post date:** [29 September 2009 17:40 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/7 "2009-09-29T17:40:24Z")

</div>

So if we were to take this further.We now have out hashMapping list

"2efa4ba470", "00000005""00000004"  
"c0784b5de101", "00000006""00000003"  
"02adecfd5c", "00000002"  
"c0784b5de101", "00000001"

Now we split the hash to give only the ID values (column 2) again doing  
some like this:

hashMapping.each do |itemDetail|  
newID = itemDetail[1].to\_s.delete("\"").strip  
end

I have another declared array in my code, with many more ID values like  
those shown above

moreIDs = ["00000001", "00000003", "00000004", "00000005", 00000007",  
"00000008"]

What I want to is search for all newID's that match moreIDs and output  
the matching ID and the corresponding code shown in column one. So the  
sample output would be like this:

"2efa4ba470", "00000005""00000004"  
"c0784b5de101", "00000003"  
"c0784b5de101", "00000001"

Show this shows the string code for an ID that is present in both of my  
lists. I had thought something like moreID == newID but that creates a  
lot off do loops. Also, thr though of array intersects crossed my mind,  
but we have a hash and array hear so I was unsure of how to make this  
work?

Any assistance in greatly appreciated.

Ne Scripter wrote:

> **···**
>
> > Ah yes, that makes perfect sense.
> > 
> > Thanks
> > 
> > Paul Smith wrote:
> > 
> > > You want a hash where the key is the element you want to group on, and  
> > > the 'item' is an array of all items with the shared key. A bit like  
> > > (untested):
> > > 
> > > hashMapping = {}
> > > 
> > > IO.foreach(source.to\_s) do |data|  
> > > &nbsp;&nbsp;&nbsp;fields = data.split(",")  
> > > &nbsp;&nbsp;&nbsp;hash = fields[0]  
> > > &nbsp;&nbsp;&nbsp;ocrID = fields[1]
> > > 
> > > &nbsp;&nbsp;&nbsp;hashMapping[ocrID] ||= #If hashMapping has never seen this key  
> > > before, make an empty array
> > > 
> > > &nbsp;&nbsp;&nbsp;hashMapping[ocrID] \<\< hash #Add the new element to the array for this  
> > > key
> > > 
> > > end
> > > 
> > > > Many thanks  
> > > > --  
> > > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).
> > > 
> > > --  
> > > Paul Smith  
> > > [http://www.nomadicfun.co.uk](http://www.nomadicfun.co.uk)
> > > 
> > > paul@pollyandpaul.co.uk
> 
> --  
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).

---

<div class="post-metadata">

**Author:** ![David\_A\_Black1](https://avatars.discourse-cdn.com/v4/letter/d/bcef8e/32.png) [@David\_A\_Black1](https://rubytalk.org/u/David_A_Black1)\
**Post date:** [30 September 2009 17:14 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/8 "2009-09-30T17:14:31Z")

</div>

I don't think you need the \* for any of them. This:

&nbsp;&nbsp;&nbsp;hash, ocrID = data.split(',')

should be fine for getting the first two values.

David

> **···**
>
> On Thu, 1 Oct 2009, Simon Krahnke wrote:
> 
> > \* Paul Smith \<paul@pollyandpaul.co.uk\> (2009-09-29) schrieb:
> > 
> > > > fields = data.split(",")  
> > > > hash = fields[0]  
> > > > ocrID = fields[1]
> > 
> > BTW, you could write this as:
> > 
> > hash, ocrID = \*data.split(",")
> > 
> > or
> > 
> > hash, ocrID, \*ignored = \*data.split(",")
> > 
> > if you want to ignore everything behind a second comma, or
> > 
> > hash, ocrID = \*data.split(",", 2)
> > 
> > if you want to include a second comma and everything behind it into the  
> > ocrID string.
> 
> --  
> David A. Black, Director  
> Ruby Power and Light, LLC ([http://www.rubypal.com](http://www.rubypal.com))  
> Ruby/Rails training, consulting, mentoring, code review  
> Book: The Well-Grounded Rubyist ([http://www.manning.com/black2\](http://www.manning.com/black2%5C))

---

<div class="post-metadata">

**Author:** ![Jesus\_Gabriel\_y\_Gala](https://avatars.discourse-cdn.com/v4/letter/j/96bed5/32.png) [@Jesus\_Gabriel\_y\_Gala](https://rubytalk.org/u/Jesus_Gabriel_y_Gala)\
**Post date:** [29 September 2009 14:47 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/9 "2009-09-29T14:47:49Z")

</div>

Using that constructor you pass a block which will be executed every  
time there's a missing key. The value of the block is used as a  
default value, but as it is in this case, it can have the side effect  
of modifying the hash. If you don't modify the hash inside the block,  
it's not modified as you can see in the first example:

Two examples:

irb(main):001:0\> h = Hash.new {|h,k| 0}  
=\> {}  
irb(main):002:0\> h[:a]  
=\> 0  
irb(main):003:0\> h[:a] += 1  
=\> 1  
irb(main):004:0\> h  
=\> {:a=\>1}  
irb(main):005:0\> h2 = Hash.new {|h,k| h[k] = }  
=\> {}  
irb(main):007:0\> h2[:a]  
=\>   
irb(main):008:0\> h2  
=\> {:a=\>}

Jesus.

> **···**
>
> On Tue, Sep 29, 2009 at 4:22 PM, Paul Smith \<paul@pollyandpaul.co.uk\> wrote:
> 
> > On Tue, Sep 29, 2009 at 2:38 PM, Robert Klemme \> \<shortcutter@googlemail.com\> wrote:
> 
> > > Even nicer
> > > 
> > > hashMapping = Hash.new {|h,k| h[k] = }
> > 
> > Is this defining a default element for the hash? I had a vague  
> > recollection you could do this but completely forgot how.

---

<div class="post-metadata">

**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\
**Post date:** [29 September 2009 14:59 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/10 "2009-09-29T14:59:00Z")

</div>

> > > hashMapping = {}
> > > 
> > > IO.foreach(source.to\_s) do |data|  
> > > fields = data.split(",")  
> > > hash = fields[0]  
> > > ocrID = fields[1]
> > > 
> > > hashMapping[ocrID] ||= #If hashMapping has never seen this key  
> > > before, make an empty array
> > > 
> > > hashMapping[ocrID] \<\< hash #Add the new element to the array for this key
> > > 
> > > end
> > 
> > It is slightly more efficient to do it in one step:
> > 
> > (hashMapping[ocrID] ||= ) \<\< hash
> > 
> > Even nicer
> > 
> > hashMapping = Hash.new {|h,k| h[k] = }
> 
> Is this defining a default element for the hash? I had a vague  
> recollection you could do this but completely forgot how.

No, this is defining a hook which is executed each time a key is  
requested which is not present. In this case the hook stores a new  
Array in the Hash but you could do other things as well.

A default value is defined via Hash.new() which does not work in  
this case for obvious reasons.

> I'd also rename the 'hash' variable to 'key' or something, I think  
> it's less confusing. Then Your hashMapping can either be given the  
> name 'hash', because that's what it is, or a name that's actually  
> useful for describing what the mystical contents of the hash are.

Absolutely. I just did not want to cause extra confusion by starting  
to rename everything. 🙂

Cheers

robert

> **···**
>
> 2009/9/29 Paul Smith \<paul@pollyandpaul.co.uk\>:
> 
> > On Tue, Sep 29, 2009 at 2:38 PM, Robert Klemme \> \<shortcutter@googlemail.com\> wrote:
> > 
> > > 2009/9/29 Paul Smith \<paul@pollyandpaul.co.uk\>:
> > > 
> > > > On Tue, Sep 29, 2009 at 12:43 PM, Ne Scripter \>\>\> \<stuart.clarke@northumbria.ac.uk\> wrote:
> 
> --  
> remember.guy do |as, often| as.you\_can - without end  
> [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/)

---

<div class="post-metadata">

**Author:** ![Ne\_Scripter](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Ne\_Scripter](https://rubytalk.org/u/Ne_Scripter)\
**Post date:** [1 October 2009 13:15 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/11 "2009-10-01T13:15:16Z")

</div>

I am having real problems with my array. As expected my array contents  
is like so:

"00000004 00000005"  
"00000003 00000006"  
"00000001"  
"00000002"

I now want 6 indivdual elements insteal of 4. I have tried to split the  
double entries up with split, however they remain together. Is there  
something fundamental I am missing? I want an array like so

array = ["00000004", "00000005", "00000003", "00000006", "00000001",  
"00000002"]

Sorry if this is simple, I have spent several hours chopping and  
changing.

Thanks

S

David A. Black wrote:

> **···**
>
> > On Thu, 1 Oct 2009, Simon Krahnke wrote:
> > 
> > > or
> > > 
> > > hash, ocrID, \*ignored = \*data.split(",")
> > > 
> > > if you want to ignore everything behind a second comma, or
> > > 
> > > hash, ocrID = \*data.split(",", 2)
> > > 
> > > if you want to include a second comma and everything behind it into the  
> > > ocrID string.
> > 
> > I don't think you need the \* for any of them. This:
> > 
> > &nbsp;&nbsp;&nbsp;hash, ocrID = data.split(',')
> > 
> > should be fine for getting the first two values.
> > 
> > David
> 
> --  
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).

---

<div class="post-metadata">

**Author:** ![Simon\_Krahnke](https://avatars.discourse-cdn.com/v4/letter/s/b782af/32.png) [@Simon\_Krahnke](https://rubytalk.org/u/Simon_Krahnke)\
**Post date:** [1 October 2009 19:35 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/12 "2009-10-01T19:35:07Z")

</div>

\* David A. Black \<dblack@rubypal.com\> (2009-09-30) schrieb:

> > \* Paul Smith \<paul@pollyandpaul.co.uk\> (2009-09-29) schrieb:
> > 
> > > > fields = data.split(",")  
> > > > hash = fields[0]  
> > > > ocrID = fields[1]
> > 
> > BTW, you could write this as:
> > 
> > hash, ocrID = \*data.split(",")
> > 
> > or
> > 
> > hash, ocrID, \*ignored = \*data.split(",")
> > 
> > if you want to ignore everything behind a second comma, or
> > 
> > hash, ocrID = \*data.split(",", 2)
> > 
> > if you want to include a second comma and everything behind it into the  
> > ocrID string.
> 
> I don't think you need the \* for any of them.

I always include it anyway, to be explicit.

> This:
> 
> &nbsp;&nbsp;hash, ocrID = data.split(',')
> 
> should be fine for getting the first two values.

Right, I just tried it. I thought you might be getting an array into  
ocrID, but you don't.

mfg, simon .... l

> **···**
>
> > On Thu, 1 Oct 2009, Simon Krahnke wrote:

---

<div class="post-metadata">

**Author:** ![Josh\_Cheek](https://avatars.discourse-cdn.com/v4/letter/j/e79b87/32.png) [@Josh\_Cheek](https://rubytalk.org/u/Josh_Cheek)\
**Post date:** [1 October 2009 14:00 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/13 "2009-10-01T14:00:13Z")

</div>

x = [  
&nbsp;&nbsp;"00000004 00000005" ,  
&nbsp;&nbsp;"00000003 00000006" ,  
&nbsp;&nbsp;"00000001" ,  
&nbsp;&nbsp;"00000002" ,  
]

x.map!{|str| str.split(/\s+/) }.flatten!

x # =\> ["00000004", "00000005", "00000003", "00000006", "00000001",  
"00000002"]

> **···**
>
> On Thu, Oct 1, 2009 at 8:15 AM, Ne Scripter \<stuart.clarke@northumbria.ac.uk \> wrote:
> 
> > I am having real problems with my array. As expected my array contents  
> > is like so:
> > 
> > "00000004 00000005"  
> > "00000003 00000006"  
> > "00000001"  
> > "00000002"
> > 
> > I now want 6 indivdual elements insteal of 4. I have tried to split the  
> > double entries up with split, however they remain together. Is there  
> > something fundamental I am missing? I want an array like so
> > 
> > array = ["00000004", "00000005", "00000003", "00000006", "00000001",  
> > "00000002"]
> > 
> > Sorry if this is simple, I have spent several hours chopping and  
> > changing.
> > 
> > Thanks
> > 
> > S
> > 
> > David A. Black wrote:  
> > \> On Thu, 1 Oct 2009, Simon Krahnke wrote:  
> > \>  
> > \>\> or  
> > \>\>  
> > \>\> hash, ocrID, \*ignored = \*data.split(",")  
> > \>\>  
> > \>\> if you want to ignore everything behind a second comma, or  
> > \>\>  
> > \>\> hash, ocrID = \*data.split(",", 2)  
> > \>\>  
> > \>\> if you want to include a second comma and everything behind it into the  
> > \>\> ocrID string.  
> > \>  
> > \> I don't think you need the \* for any of them. This:  
> > \>  
> > \> hash, ocrID = data.split(',')  
> > \>  
> > \> should be fine for getting the first two values.  
> > \>  
> > \>  
> > \> David
> > 
> > --  
> > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).

---

<div class="post-metadata">

**Author:** ![David\_A\_Black1](https://avatars.discourse-cdn.com/v4/letter/d/bcef8e/32.png) [@David\_A\_Black1](https://rubytalk.org/u/David_A_Black1)\
**Post date:** [1 October 2009 14:05 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/14 "2009-10-01T14:05:44Z")

</div>

Hi --

> **···**
>
> On Thu, 1 Oct 2009, Josh Cheek wrote:
> 
> > On Thu, Oct 1, 2009 at 8:15 AM, Ne Scripter \<stuart.clarke@northumbria.ac.uk \>\> wrote:
> > 
> > > I am having real problems with my array. As expected my array contents  
> > > is like so:
> > > 
> > > "00000004 00000005"  
> > > "00000003 00000006"  
> > > "00000001"  
> > > "00000002"
> > > 
> > > I now want 6 indivdual elements insteal of 4. I have tried to split the  
> > > double entries up with split, however they remain together. Is there  
> > > something fundamental I am missing? I want an array like so
> > > 
> > > array = ["00000004", "00000005", "00000003", "00000006", "00000001",  
> > > "00000002"]
> > > 
> > > Sorry if this is simple, I have spent several hours chopping and  
> > > changing.
> > 
> > x = [  
> > "00000004 00000005" ,  
> > "00000003 00000006" ,  
> > "00000001" ,  
> > "00000002" ,  
> > ]
> > 
> > x.map!{|str| str.split(/\s+/) }.flatten!
> > 
> > x # =\> ["00000004", "00000005", "00000003", "00000006", "00000001",  
> > "00000002"]
> 
> You can even dispense with the argument to split if it's just  
> whitespace.
> 
> Another option, though perhaps a slightly memory-wasting one:
> 
> &nbsp;&nbsp;&nbsp;x.join(' ').split
> 
> David
> 
> --  
> David A. Black, Director  
> Ruby Power and Light, LLC ([http://www.rubypal.com](http://www.rubypal.com))  
> Ruby/Rails training, consulting, mentoring, code review  
> Book: The Well-Grounded Rubyist ([http://www.manning.com/black2\](http://www.manning.com/black2%5C))

---

<div class="post-metadata">

**Author:** ![Ne\_Scripter](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Ne\_Scripter](https://rubytalk.org/u/Ne_Scripter)\
**Post date:** [1 October 2009 14:47 UTC](https://rubytalk.org/t/group-by-unique-entries-of-a-hash/55592/15 "2009-10-01T14:47:38Z")

</div>

Ah map. Perfect.

Josh Cheek wrote:

> **···**
>
> > On Thu, Oct 1, 2009 at 8:15 AM, Ne Scripter \> \<stuart.clarke@northumbria.ac.uk \>\> wrote:
> > 
> > > something fundamental I am missing? I want an array like so
> > > 
> > > \>\>  
> > > \> David
> > > 
> > > --  
> > > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).
> > 
> > x.map!{|str| str.split(/\s+/) }.flatten!
> > 
> > x # =\> ["00000004", "00000005", "00000003", "00000006", "00000001",  
> > "00000002"]
> 
> --  
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).