You can use the `os` gem:

    gem install os

And then

    require &#39;os&#39;
    OS.linux?   #=&gt; true or false
    OS.windows? #=&gt; true or false
    OS.java?    #=&gt; true or false
    OS.bsd?     #=&gt; true or false
    OS.mac?     #=&gt; true or false
    # and so on.

See: [https://github.com/rdp/os](https://github.com/rdp/os)

Here is the best one I have seen recently.  It is from selenium.  The reason I think it is the best is it uses rbconfig host_os field which has the advantage of working on MRI and JRuby.  RUBY_PLATFORM will say &#39;java&#39; on JRuby regardless of host os it is running on.  You will need to mildly tweak this method:

      require &#39;rbconfig&#39;

      def os
        @os ||= (
          host_os = RbConfig::CONFIG[&#39;host_os&#39;]
          case host_os
          when /mswin|msys|mingw|cygwin|bccwin|wince|emc/
            :windows
          when /darwin|mac os/
            :macosx
          when /linux/
            :linux
          when /solaris|bsd/
            :unix
          else
            raise Error::WebDriverError, &quot;unknown os: #{host_os.inspect}&quot;
          end
        )
      end


You can use  
  

`puts RUBY_PLATFORM`

    irb(main):001:0&gt; RUBY_PLATFORM
    =&gt; &quot;i686-linux&quot;

But @Pete is right.

You can inspect the **RUBY_PLATFORM** constant, but this is known to be unreliable in certain cases, such as when running JRuby. Other options include capturing the output of the `uname -a` command on POSIX systems, or using a detection gem such as [sys-uname][1].

  [1]: https://github.com/djberg96/sys-uname

I do not want [d3.behavior.zoom][1] to add the ability to double click zoom on my graph. How can I disable this behavior?

Here is a [JSFiddle][2] with the unwanted behavior.

I have tried the following without any luck.

     d3.behavior.zoom.dblclick = function() {};



  [1]: https://github.com/mbostock/d3/wiki/Zoom-Behavior#wiki-zoom
  [2]: http://jsfiddle.net/brantolsen/Ld6Uz/

How to disable double click zoom for d3.behavior.zoom?

Why doesn&#39;t `Decimal` data type have `Epsilon` field?

[From the manual](https://msdn.microsoft.com/en-us/library/364x0z75.aspx), the range of `decimal` values is &#177;1.0 &#215; 10e−28 to &#177;7.9 &#215; 10e28.

[The description of `Double.Epsilon`](https://msdn.microsoft.com/en-us/library/system.double.epsilon.aspx):

&gt; Represents the smallest positive `Double` value greater than zero

So it seems, `Decimal` has such a (non-trivial) value too. But why isn&#39;t it easily accessible?

I do understand that +1.0 &#215; 10e−28 is exactly the smallest positive Decimal value greater than zero:

    decimal Decimal_Epsilon = new decimal(1, 0, 0, false, 28); //1e-28m;

By the way, there are a couple of questions that give information about Decimal data type&#39;s internal representation:

 - https://stackoverflow.com/questions/10614592/decimal-in-c-sharp-misunderstanding 
 - https://stackoverflow.com/questions/11241842/whats-the-second-minimum-value-that-a-decimal-can-represent

Here&#39;s an example where `Epsilon` would be useful.

Lets say I have a weighted sum of values from some sampling set and sum of weights (or count) of samples taken. Now I want to compute the weighted mean value. But I know that the sum of weights (or count) may be still zero. To prevent division by zero I could do `if... else...` and check for the zero. Or I could write like this:

    T weighted_mean = weighted_sum / (weighted_count + T.Epsilon)

This code is shorter in my eye. Or, alternatively I can skip the `+ T.Epsilon` and instead initialize with:

    T weighted_count = T.Epsilon;

I can do this when I know that the values of real weights are never close to `Epsilon`.

And for some data types and use cases this is maybe even faster since it does not involve branches. As I understand, the processors are not able to take both branches for computation, even when the branches are short. And I may know that the zeros occur randomly at 50% rate :=) For `Decima`l, the speed aspect is likely not important or even positively useful in the first case though.

My code may be generic (for example, generated) and I do not want to write separate code for decimals. Therefore one would like to see that `Decimal` have similar interface as other real-valued types.

C# Decimal.Epsilon

Is there a way to detect the operating system in ruby? I am working on developing a sketchup tool that will need to detect Mac vs. Windows. 

Detecting Operating Systems in Ruby

<p>Is there a way to detect the operating system in ruby? I am working on developing a sketchup tool that will need to detect Mac vs. Windows.</p>


I have an array of hashes like so:

     [{&quot;testPARAM1&quot;=&gt;&quot;testVAL1&quot;}, {&quot;testPARAM2&quot;=&gt;&quot;testVAL2&quot;}]

And I&#39;m trying to map this onto single hash like this:

    {&quot;testPARAM2&quot;=&gt;&quot;testVAL2&quot;, &quot;testPARAM1&quot;=&gt;&quot;testVAL1&quot;}

I have achieved it using

      par={}
      mitem[&quot;params&quot;].each { |h| h.each {|k,v| par[k]=v} } 

But I was wondering if it&#39;s possible to do this in a more idiomatic way (preferably without using a local variable).

How can I do this?


Rails mapping array of hashes onto single hash

What is the fastest way to check if a string matches a regular expression in Ruby?

My problem is that I have to &quot;egrep&quot; through a huge list of strings to find which are the ones that match a regexp that is given at runtime. **I only care about whether the string matches the regexp, not where it matches, nor what the content of the matching groups is.** I hope this assumption can be used to reduce the amount of time my code spend matching regexps.

I load the regexp with

    pattern = Regexp.new(ptx).freeze

I have found that `string =~ pattern` is slightly faster than `string.match(pattern)`.

Are there other tricks or shortcuts that can used to make this test even faster?

Fastest way to check if a string matches a regexp in ruby?

Please help me get all instance variables declared in a class the same way `instance_methods` shows me all methods available in a class.

    class A
      attr_accessor :ab, :ac
    end
    
    puts A.instance_methods  #gives ab and ac
    
    puts A.something         #gives me @ab @ac...

Get all instance variables declared in class

I&#39;m struggling to find a comparison of includes() and preload() for ActiveRecord objects. Can anyone explain the difference ?

What&#39;s the difference between “includes” and “preload” in an ActiveRecord query?

How can I convert a hash into a struct in ruby?

Given this:

    h = { :a =&gt; 1, :b =&gt; 2 }

I want a struct such that:

    s.a == 1
    s.b == 2

Convert a hash into a struct

For Linux this would give me `/`, for Windows on the C drive that would give me `C:\\`. Note that python is not necessarily installed on the C drive on windows.

A system independent way using python to get the root directory/drive on which python is installed

I&#39;m sure mutex isn&#39;t enough that&#39;s the reason the concept of condition variables exist; but it beats me and I&#39;m not able to convince myself with a concrete scenario when a condition variable is essential.

https://stackoverflow.com/questions/1055398/differences-between-conditional-variables-mutexes-and-locks question&#39;s accepted answer says that a condition variable is a 

&gt; lock with a &quot;signaling&quot; mechanism. It is used when threads need to
&gt; wait for a resource to become available. A thread can &quot;wait&quot; on a CV
&gt; and then the resource producer can &quot;signal&quot; the variable, in which
&gt; case the threads who wait for the CV get notified and can continue
&gt; execution

Where I get confused is that, a thread can wait on a mutex too, and when it gets signalled, is simply means the variable is now available, why would I need a condition variable?

P.S.: Also, a mutex is required to guard the condition variable anyway, when makes my vision more askew towards not seeing condition variable&#39;s purpose.

When is a condition variable needed, isn&#39;t a mutex enough?

Is there any good way to get the remaining memory available to the JVM at run time? The use case of this would be to have web services which fail gracefully when they are nearing their memory limits by refusing new connections with a nice error message &quot;too many people using this, try again later&quot;, rather than dying abruptly with an OutOfMemory error.

Note this has nothing to do with calculating/estimating the cost of each object beforehand. In principle I could estimate how much memory my objects take and refuse new connections based on that estimate, but that seems kind of hacky/fragile.



Java get available memory

I am learning about operating systems but there is a small concept I cannot grasp. Say a process 1 is running on the CPU and then it issues an I/O request to read from a disk. For efficiency, the CPU begins executing process 2 as this request is handled. That all makes sense but doesn&#39;t the I/O need to use the CPU?

![enter image description here][1]


  [1]: http://i.stack.imgur.com/52in9.png

&lt;strong&gt;My Question:&lt;/strong&gt; Why isn&#39;t the CPU needed to service process 1&#39;s request?

Why is the CPU not needed to service I/O requests?

I am often confused with the concept of virtualization in operating systems. Considering RAM as the physical memory, why do we need the virtual memory for executing a process?

Where does this virtual memory stand when the process (program) from the external hard drive is brought to the main memory (physical memory) for the execution.

Who takes care of the virtual memory and what is the size of the virtual memory?

Suppose if the size of the RAM is 4GB (i.e. 2^32-1 address spaces) what is the size of the virtual memory?

What are the differences between virtual memory and physical memory?

After upgrading to OS X Yosemite I found that eclipse was not working because JAVA was not properly installed. I installed it and now I am able to open eclipse. 

When I connect my device, I am able to see my device on the device list in eclipse. However when I run my project, I am unable to see it on Android device chooser. My device is getting detected by Eclipse but I am not able to select it to run.

This was working perfectly on my previous OS X Mavericks! Please help!

Thanks

Just upgraded my OS X to Yosemite, Android Device Chooser not showing device - what to do?

In computer vision and object detection, the common evaluation method is mAP. 
What is it and how is it calculated?

Content Type	Original Author	Original Content on Stackoverflow
Question	user1546594	View Question on Stackoverflow
Solution 1 - Ruby	debbie	View Answer on Stackoverflow
Solution 2 - Ruby	Thomas Enebo	View Answer on Stackoverflow
Solution 3 - Ruby	InternetSeriousBusiness	View Answer on Stackoverflow
Solution 4 - Ruby	Todd A. Jacobs	View Answer on Stackoverflow

Detecting Operating Systems in Ruby

Ruby Problem Overview

Ruby Solutions

Solution 1 - Ruby

Solution 2 - Ruby

Solution 3 - Ruby

Solution 4 - Ruby

C# Decimal.Epsilon

How to disable double click zoom for d3.behavior.zoom?

Attributions