You can do `count` on `line_items` which will return you an ordered hash of `device_id` and `count`.

    @project.line_items.group(:device_id).count


hash of devise_id as key and associated records count

    @project.line_items.group(:device_id).count



Just add a `:select` option:

    @line_items = @project.line_items.all(
      :group  =&gt; &quot;device_id&quot;,
      :select =&gt; &quot;device_id, COUNT(*) as count&quot;
    )

Then each `@line_item` will have a `count` attribute.

I think you can try this as well.

    @project.line_items.group(:device_id).pluck(&quot;device_id, count(device_id)&quot;)

^^ This gives array of arrays with elements &#39;device_id and count&#39;


something like

     User.all(:joins =&gt; :comments, :select =&gt; &quot;users.*, count(comments.id) as comments_count&quot;, :group =&gt; &quot;users.id&quot;)


might also work...

After this commit:

https://github.com/rails/rails/commit/a1c05dd8b9bd3623289d3aa73dda2943d620cc34

there&#39;s a new way to do the same thing:

    @project.line_items.count(:group =&gt; LineItem.arel_table[:device_id])

For only count **pluck** would be faster here rather than **group**

    @project.line_items.pluck(:device_id).count


    @project.line_items.pluck(:device_id).uniq.count

I&#39;m trying to remove an item from an `ArrayList` and I get this Exception:  
`Collection was modified; enumeration operation may not execute.` 
 
Any ideas?

Collection was modified; enumeration operation may not execute in ArrayList

I&#39;m trying to collect string values in a bash script. What&#39;s the simplest way that I can append string values to a list or array structure such that I can echo them out at the end?

Mutable list or array structure in Bash? How can I easily append to it?

I know I&#39;ve seen this before but I can&#39;t find anything now. I want to group a query by a certain column and be able to display how many are in each group. I got the first part down:  

    @line_items = @project.line_items.all(:group =&gt; &quot;device_id&quot;)  

This is for my line item index view, which is just a table displaying the line items. How do I make a column in that table for &quot;count&quot; now that the line items are grouped by device?

Group and count in Rails

I know I've seen this before but I can't find anything now. I want to group a query by a certain column and be able to display how many are in each group. I got the first part down:
<pre><code class="hljs language-less">@line_items = @project.line_items.all(:group => "device_id") 
</code></pre>
This is for my line item index view, which is just a table displaying the line items. How do I make a column in that table for "count" now that the line items are grouped by device?

I have a two-part question about form_for and nested resources. Let&#39;s say I&#39;m writing a blog engine and I want to relate a comment to an article. I&#39;ve defined a nested resource as follows:

    map.resources :articles do |articles|
        articles.resources :comments
    end

The comment form is in the show.html.erb view for articles, underneath the article itself, for instance like this:

    &lt;%= render :partial =&gt; &quot;articles/article&quot; %&gt;
    &lt;% form_for([ :article, @comment]) do |f| %&gt;
        &lt;%= f.text_area :text %&gt;
        &lt;%= submit_tag &quot;Submit&quot; %&gt;
    &lt;%  end %&gt;

This gives an error, &quot;Called id for nil, which would mistakenly etc.&quot; I&#39;ve also tried

    &lt;% form_for @article, @comment do |f| %&gt;

Which renders correctly but relates f.text_area to the article&#39;s &#39;text&#39; field instead of the comment&#39;s, and presents the html for the article.text attribute in that text area. So I seem to have this wrong as well. What I want is a form whose &#39;submit&#39; will call the create action on CommentsController, with an article_id in the params, for instance a post request to /articles/1/comments. 

The second part to my question is, what&#39;s the best way to create the comment instance to begin with? I&#39;m creating a @comment in the show action of the ArticlesController, so a comment object will be in scope for the form_for helper. Then in the create action of the CommentsController, I create new @comment using the params passed in from the form_for. 

Thanks!

form_for with nested resources

I&#39;m having problems rounding.  I have a float, which I want to round to the hundredth of a decimal.  However, I can only use `.round` which basically turns it into an int, meaning `2.34.round # =&gt; 2.`  Is there a simple effect way to do something like `2.3465 # =&gt; 2.35`


Ruby: Rounding float in Ruby

I know this is a [duplicate][1], however, the Grails world has moved on considerably since that question was asked more than a year ago, as has the IDE support in Eclipse, so please don&#39;t just blindly close it.  

I thought the answer was yes and have embarked on a new project with [Grails 1.2.0][2] and have flirted with the Groovy/Grails bits of the [STS Eclipse Integration][3].

I think the question deserves revisiting after a year of Grails evolution, when the answer was definitely mixed.

So, as an experienced Java web developer I have these questions and would appreciate *my assumptions* being challenged:

 - Is Grails now worth it vs. Ruby or roll your own?
 - Has it overcome its buggy start?  
 - Does it really confer rapid development benefits?  *(I admit I am struggling now I am past the extensive baseline configuration to make my bespoke app which is not list and page oriented)*
 - Does it perform for real world production apps?  *(It feels heavy)*
 - Is the Eclipse plug-in better than it was and fit for purpose? *(I think not yet)*

Thanks

**EDIT:**
I am learning as I go and I have a couple of significant gripes to make about living with the framework - rather than framework capabilities themselves.  I am adding these because I think they should be considerations and are based on my experience and opinion, and may help someone who is trying to decide whether to go grails.  I may also be showing my lack of experience with the framework, so none of this is meant as out and out criticisms.  I am an experienced developer and this is what I have found:  

**Debugging is really hard**.  In fact it is almost impossible, especially as a beginner in the framework, which is when you need your trusty debugger friend the most.  I have spent way more time than I ought to tracking down problems of syntactical errors in some part of the code to do with referring to domain fields which cause silent failures somewhere in the stack.

**Logging is frankly awful**.  You have two modes, &quot;nothing useful&quot; and &quot;an inordinate amount of useless stuff&quot;. My debug log was 128Mb after a single page request and contains nothing about my error.  The whole issue of logging needs reconsideration in the framework in my opinion.

**The STS Eclipse IDE is of marginal value**.  Other than syntax hilighting it is not much use.  You can&#39;t debug the code so it is a glorified editor.  The code hints are patchy and there is no GSP support at all as far as I can see.  It also is the slowest Eclipse plug-in I have on my desktop - by about 2 minutes to start up.  It is shockingly slow.  I have reverted to a text editor (which you&#39;ll notice all the online tutorial videos do too) and some custom syntax hilighting.

**I have some serious concerns about performance**.  A bit too early to say, but I am already finding myself tweaking the database because of hibernate.  Perhaps that&#39;s to be expected, but I am really having to keep my domain model simple for the conventions to yield performant queries.

And one last one, the convention that your logical domain model and your physical database model should be identical is not a smart default and unlikely ever to be the case in the real world.  I know you can separate the two, but it creates a degree of complexity which I think could be avoided if the conventions were extended.  There is inadequate documentation about composition and [what you need to do to make it work in practice][4].  


  [1]: https://stackoverflow.com/questions/397228/is-grails-worth-it
  [2]: http://www.grails.org/1.2+Release+Notes
  [3]: http://www.grails.org/STS+Integration
  [4]: https://stackoverflow.com/questions/2123871/how-do-i-save-a-composite-field-value-in-grails-gsp/

Is Grails (now) worth it?

Is it possible to set up a double relationship in `activerecord` models via the `generate scaffold` command?

For example, if I had a `User` model and a `PrivateMessage` model, the private_messages table would need to keep track of both the `sender` and `recipient`.

Obviously, for a single relationship I would just do this:

    ruby script/generate scaffold pm title:string content:string user:references

Is there a similar way to set up two relations?

Also, is there anyway to set up aliases for the relations?

So rather than saying:

    @message.user

You can use something like:

  `@message.sender` or `@message.recipient`

Any advice would be greatly appreciated.

Thanks.

Ruby on rails - Reference the same model twice?

I&#39;ve been a bad kid and used the following syntax in my partial templates to set default values for local variables if a value wasn&#39;t explicitly defined in the :locals hash when rendering the partial -- 

    &lt;% foo = default_value unless (defined? foo) %&gt;

This seemed to work fine until recently, when (for no reason I could discern) non-passed variables started behaving as if they had been defined to nil (rather than undefined).

As has been pointed by various helpful people on SO, http://api.rubyonrails.org/classes/ActionView/Base.html says *not* to use

    defined? foo

and instead to use

    local_assigns.has_key? :foo
  
I&#39;m trying to amend my ways, but that means changing a lot of templates.  

Can/should I just charge ahead and make this change in all the templates?  Is there any trickiness I need to watch for?  How diligently do I need to test each one?

optional local variables in rails partial templates: how do I get out of the (defined? foo) mess?

Imagine you sell those metallic digits used to number houses, locker doors, hotel rooms, etc. You need to find how many of each digit to ship when your customer needs to number doors/houses:

- 1 to 100
- 51 to 300
- 1 to 2,000 with zeros to the left

The obvious solution is to do a loop from the first to the last number, convert the counter to a string with or without zeros to the left, extract each digit and use it as an index to increment an array of 10 integers.

I wonder if there is a better way to solve this, without having to loop through the entire integers range.

Solutions in any language or pseudocode are welcome.

&lt;hr&gt;

Edit:  
-----  

**Answers review**  
*John at CashCommons* and *Wayne Conrad* comment that my current approach is good and fast enough. Let me use a silly analogy: If you were given the task of counting the squares in a chess board in less than 1 minute, you could finish the task by counting the squares one by one, but a *better* solution is to count the sides and do a multiplication, because you later may be asked to count the tiles in a building.  
*Alex Reisner* points to a very interesting mathematical law that, unfortunately, doesn’t seem to be relevant to this problem.  
*Andres* suggests the same algorithm I’m using, but extracting digits with %10 operations instead of substrings.  
*John at CashCommons* and *phord* propose pre-calculating the digits required and storing them in a lookup table or, for raw speed, an array. This could be a good solution if we had an absolute, unmovable, set in stone, maximum integer value. I’ve never seen one of those.  
*High-Performance Mark*  and *strainer* computed the needed digits for various ranges. The result for one millon seems to indicate there is a proportion, but the results for other number show different proportions.  
*strainer* found some formulas that may be used to count digit for number which are a power of ten.
*Robert Harvey* had a very interesting experience posting the question at MathOverflow. One of the math guys wrote a solution using mathematical notation.  
*Aaronaught* developed and tested a solution using mathematics. After posting it he reviewed the formulas originated from Math Overflow and found a flaw in it (point to Stackoverflow :).  
*noahlavine* developed an algorithm and presented it in pseudocode.  

**A new solution**  
After reading all the answers, and doing some experiments, I found that for a range of integer from 1 to 10&lt;sup&gt;n&lt;/sup&gt;-1:  

- For digits 1 to 9, n*10&lt;sup&gt;(n-1)&lt;/sup&gt; pieces are needed 
- For digit 0, if not using leading zeros, n*10&lt;sup&gt;n-1&lt;/sup&gt; - ((10&lt;sup&gt;n&lt;/sup&gt;-1) / 9) are needed
- For digit 0, if using leading zeros,  n*10&lt;sup&gt;n-1&lt;/sup&gt; - n are needed

The first formula was found by *strainer* (and probably by others), and I found the other two by trial and error (but they may be included in other answers).

For example, if n = 6, range is 1 to 999,999:

- For digits 1 to 9 we need 6*10&lt;sup&gt;5&lt;/sup&gt; = 600,000 of each one
- For digit 0, without leading zeros, we need 6*10&lt;sup&gt;5&lt;/sup&gt; – (10&lt;sup&gt;6&lt;/sup&gt;-1)/9 = 600,000 - 111,111 = 488,889
- For digit 0, with leading zeros, we need 6*10&lt;sup&gt;5&lt;/sup&gt; – 6 = 599,994

These numbers can be checked using *High-Performance Mark* results. 

Using these formulas, I improved the original algorithm. It still loops from the first to the last number in the range of integers, but, if it finds a number which is a power of ten, it uses the formulas to add to the digits count the quantity for a full range of 1 to 9 or 1 to 99 or 1 to 999 etc. Here&#39;s the algorithm in pseudocode:

&lt;pre&gt;integer First,Last //First and last number in the range
integer Number     //Current number in the loop
integer Power      //Power is the n in 10^n in the formulas
integer Nines      //Nines is the resut of 10^n - 1, 10^5 - 1 = 99999
integer Prefix     //First digits in a number. For 14,200, prefix is 142
array 0..9  Digits //Will hold the count for all the digits

FOR Number = First TO Last
  CALL TallyDigitsForOneNumber WITH Number,1  //Tally the count of each digit 
                                              //in the number, increment by 1
  //Start of optimization. Comments are for Number = 1,000 and Last = 8,000.
  Power = Zeros at the end of number //For 1,000, Power = 3
  IF Power &gt; 0                       //The number ends in 0 00 000 etc 
    Nines = 10^Power-1                 //Nines = 10^3 - 1 = 1000 - 1 = 999
    IF Number+Nines &amp;lt;= Last            //If 1,000+999 &amp;lt; 8,000, add a full set
      Digits[0-9] += Power*10^(Power-1)  //Add 3*10^(3-1) = 300 to digits 0 to 9
      Digits[0]   -= -Power              //Adjust digit 0 (leading zeros formula)
      Prefix = First digits of Number    //For 1000, prefix is 1
      CALL TallyDigitsForOneNumber WITH Prefix,Nines //Tally the count of each 
                                                     //digit in prefix,
                                                     //increment by 999
      Number += Nines                    //Increment the loop counter 999 cycles
    ENDIF
  ENDIF 
  //End of optimization
ENDFOR  

SUBROUTINE TallyDigitsForOneNumber PARAMS Number,Count
  REPEAT
    Digits [ Number % 10 ] += Count
    Number = Number / 10
  UNTIL Number = 0
&lt;/pre&gt;

For example, for range 786 to 3,021, the counter will be incremented:

- By 1 from 786 to 790 (5 cycles)
- By 9 from 790 to 799 (1 cycle)
- By 1 from 799 to 800
- By 99 from 800 to 899
- By 1 from 899 to 900
- By 99 from 900 to 999
- By 1 from 999 to 1000
- By 999 from 1000 to 1999
- By 1 from 1999 to 2000
- By 999 from 2000 to 2999
- By 1 from 2999 to 3000
- By 1 from 3000 to 3010 (10 cycles)
- By 9 from 3010 to 3019 (1 cycle)
- By 1 from 3019 to 3021 (2 cycles)

Total: 28 cycles
Without optimization: 2,235 cycles

Note that this algorithm solves the problem without leading zeros. To use it with leading zeros, I used a hack:

&gt; If range 700 to 1,000 with leading zeros is needed, use the algorithm for 10,700 to 11,000 and then substract 1,000 - 700 = 300 from the count of digit 1.


**Benchmark and Source code**  

I tested the original approach, the same approach using %10 and the new solution for some large ranges, with these results:

&lt;pre&gt;
Original             104.78 seconds
With %10              83.66
With Powers of Ten     0.07
&lt;/pre&gt;

A screenshot of the benchmark application:  
[![alt text][2]][2]  
&lt;sub&gt;(source: [clarion.sca.mx](http://clarion.sca.mx/images/stories/digitsbench.png))&lt;/sub&gt;  


If you would like to see the full source code or run the benchmark, use these links:  

- Complete Source code (in [Clarion][1]): &lt;http://sca.mx/ftp/countdigits.txt&gt;
- Compilable project and win32 exe: &lt;http://sca.mx/ftp/countdigits.zip&gt;

**Accepted answer**  

*noahlavine* solution may be correct, but l just couldn’t follow the pseudo code, I think there are some details missing or not completely explained.  

*Aaronaught* solution seems to be correct, but the code is just too complex for my taste.  

I accepted *strainer*’s answer, because his line of thought guided me to develop this new solution.


  [1]: http://clarion.sca.mx/What-is-Clarion
  [2]: https://i.stack.imgur.com/eMSnq.png

How to count each digit in a range of integers?

how do I write this query in linq (vb.net)?

    
     select B.Name
     from Company B
     group by B.Name
     having COUNT(1) &gt; 1

Linq with group by having count

This question came to my mind, when I had something like

    enum Folders {FA, FB, FC};
and wanted to create an array of containers for each folder:

    ContainerClass*m_containers[3];
    ....
    m_containers[FA] = ...; // etc.
(Using maps it&#39;s much more elegant to use: `std::map&lt;Folders, ContainerClass*&gt; m_containers;`)

But to come back to my original question: What if I do not want to hard-code the array size, is there a way to figure out how many items are in Folders? (Without relying on e.g. `FC` being the last item in the list which would allow something like `ContainerClass*m_containers[FC+1]` if I&#39;m not mistaken.)

(How) can I count the items in an enum?

In Python, how do you find the number of digits in an integer?


How to find length of digits in an integer?

I have a a dictionary mapping keywords to the repetition of the keyword, but I only want a list of distinct words so I wanted to count the number of keywords. Is there a way to count the number of keywords or is there another way I should look for distinct words?

Content Type	Original Author	Original Content on Stackoverflow
Question	tladuke	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Chandra Patni	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	Sandip Ransing	View Answer on Stackoverflow
Solution 3 - Ruby on-Rails	Alex Reisner	View Answer on Stackoverflow
Solution 4 - Ruby on-Rails	bluefoggy	View Answer on Stackoverflow
Solution 5 - Ruby on-Rails	rogerdpack	View Answer on Stackoverflow
Solution 6 - Ruby on-Rails	Psylone	View Answer on Stackoverflow
Solution 7 - Ruby on-Rails	John Smith	View Answer on Stackoverflow

Group and count in Rails

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

Solution 3 - Ruby on-Rails

Solution 4 - Ruby on-Rails

Solution 5 - Ruby on-Rails

Solution 6 - Ruby on-Rails

Solution 7 - Ruby on-Rails

Mutable list or array structure in Bash? How can I easily append to it?

Collection was modified; enumeration operation may not execute in ArrayList

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