Try this:

    my_array.find{|x| x.some_test }

Or here&#39;s a shortcut (thanks @LarsHaugseth for reminding about it)

    my_array.find(&amp;:some_test)

As for me find sounds confusing. As i am expecting receive more than one object for such a request. 

I prefer to use `detect` for getting distinct one.

And `select` for finding all of them.

Here what ruby docs tells about them:

    detect(ifnone = nil) {| obj | block } → obj or nil click to toggle source 
    find(ifnone = nil) {| obj | block } → obj or nil 
    detect(ifnone = nil) → an_enumerator 
    find(ifnone = nil) → an_enumerator

Passes each entry in enum to block. Returns the first for which block is not false. If no object matches, calls ifnone and returns its result when it is specified, or returns nil otherwise.



    find_all {| obj | block } → array click to toggle source
    select {| obj | block } → array
    find_all → an_enumerator
    select → an_enumerator

Returns an array containing all elements of enum for which block is not false


What is the meaning of the `~.` argument in R?

For example `plot(~.,xyz..)`

I have seen this argument used several times in various contexts and since it is difficult to meaningfully search for symbols on google, I have met little success. 


Meaning of ~. (tilde dot) argument?

Here is how the error output is if I run `virtualbox` from the terminal. How to correct it? I am on a Ubuntu 12.10 64bit machine.

    virtualbox
    WARNING: The character device /dev/vboxdrv does not exist.
    	 Please install the virtualbox-ose-dkms package and the appropriate
    	 headers, most likely linux-headers-generic.
    
    	 You will not be able to start VMs until this problem is fixed.

EDIT:

I have both the latest `linux-headers-generic` and `virtualbox-ose-dkms` packages

How to correct virtualbox installation

Is there a shorter way to find the first element in an array meeting some conditions than this:

    my_array[ my_array.index {|x| x.some_test} ]


First element of an array with condition

<p>Is there a shorter way to find the first element in an array meeting some conditions than this:</p>
<pre><code class="hljs language-css">my_array<span class="hljs-selector-attr">[ my_array.index {|x| x.some_test} ]</span>
</code></pre>


In python there is a `pass` keyword for defining an empty function, condition, loop, ...
Is there something similar for Ruby?

Python Example:

    def some_function():
        # do nothing
        pass

Equivalent of “pass” in Ruby

I have a `map` which either changes a value or sets it to nil. I then want to remove the nil entries from the list. The list doesn&#39;t need to be kept.

This is what I currently have:

&lt;!-- language: lang-rb --&gt;

    # A simple example function, which returns a value or nil
    def transform(n)
      rand &gt; 0.5 ? n * 10 : nil }
    end
    
    items.map! { |x| transform(x) } # [1, 2, 3, 4, 5] =&gt; [10, nil, 30, 40, nil]
    items.reject! { |x| x.nil? } # [10, nil, 30, 40, nil] =&gt; [10, 30, 40]

I&#39;m aware I could just do a loop and conditionally collect in another array like this:

&lt;!-- language: lang-rb --&gt;

    new_items = []
    items.each do |x|
        x = transform(x)
        new_items.append(x) unless x.nil?
    end
    items = new_items

But it doesn&#39;t seem that idiomatic. Is there a nice way to map a function over a list, removing/excluding the nils as you go?

How to map and remove nil values in Ruby

I need to make the first character of every word uppercase, and make the rest lowercase...

    manufacturer.MFA_BRAND.first.upcase

is only setting the first letter uppercase, but I need this:

    ALFA ROMEO =&gt; Alfa Romeo
    AUDI =&gt; Audi
    BMW =&gt; Bmw
    ONETWO THREE FOUR =&gt; Onetwo Three Four

Ruby capitalize every word first letter

How can I write a Ruby function that splits the input by any kind of whitespace, and remove all the whitespace from the result? For example, if the input is

     aa bbb
    cc    dd ee

Then return an array `[&quot;aa&quot;, &quot;bbb&quot;, &quot;cc&quot;, &quot;dd&quot;, &quot;ee&quot;]`.

Ruby split by whitespace

I need a way to check if an object is an instance of another object using RSpec. For example:

    describe &quot;new shirt&quot; do
      it &quot;should be an instance of a Shirt object&quot;
        # How can i check if it is an instance of a shirt object
      end
    end

Using RSpec to check if something is an instance of another object

**Background**

My question is motivated by simple observations, which somewhat undermine the beliefs/assumptions often held/made by experienced MATLAB users:

 - MATLAB is very well optimized when it comes to the built-in functions and the fundamental language features, such as indexing vectors and matrices.
 - Loops in MATLAB are slow (despite the JIT) and should generally be avoided if the algorithm can be expressed in a native, &#39;vectorized&#39; manner. 

The bottom line: core MATLAB functionality is efficient and trying to outperform it using MATLAB code is hard, if not impossible.


**Investigating performance of vector indexing**

The example codes shown below are as fundamental as it gets: I assign a scalar value to all vector entries. First, I allocate an empty vector `x`:

    tic; x = zeros(1e8,1); toc
    Elapsed time is 0.260525 seconds.

Having `x` I would like to set all its entries to the same value. In practice you would do it differently, e.g., `x = value*ones(1e8,1)`, but the point here is to investigate the performance of vector indexing. The simplest way is to write:

    tic; x(:) = 1; toc
    Elapsed time is 0.094316 seconds.

Let&#39;s call it method 1 (from the value assigned to `x`). It seems to be very fast (faster at least than memory allocation). Because the only thing I do here is operate on memory, I can estimate the efficiency of this code by calculating the obtained *effective memory bandwidth* and comparing it to the *hardware memory bandwidth* of my computer:

    eff_bandwidth = numel(x) * 8 bytes per double * 2 / time

In the above, I multiply by `2` because unless SSE streaming is used, setting values in memory requires that the vector is both read from and written to the memory. In the above example:

    eff_bandwidth(1) = 1e8*8*2/0.094316 = 17 Gb/s

[STREAM-benchmarked memory bandwidth](https://www.cs.virginia.edu/stream/) of my computer is around 17.9 Gb/s, so indeed - MATLAB delivers close to peak performance in this case! So far, so good.

Method 1 is suitable if you want to set *all* vector elements to some value. But if you want to access elements every `step` entries, you need to substitute the `:` with e.g., `1:step:end`. Below is a direct speed comparison with method 1:

    tic; x(1:end) = 2; toc
    Elapsed time is 0.496476 seconds.

While you would not expect it to perform any different, method 2 is clearly big trouble: factor 5 slowdown for no reason. My suspicion is that in this case MATLAB explicitly allocates the index vector (`1:end`). This is somewhat confirmed by using explicit vector size instead of `end`:

    tic; x(1:1e8) = 3; toc
    Elapsed time is 0.482083 seconds.

Methods 2 and 3 perform equally bad.

Another possibility is to explicitly create an index vector `id` and use it to index `x`. This gives you the most flexible indexing capabilities. In our case:

    tic;
    id = 1:1e8; % colon(1,1e8);
    x(id) = 4;
    toc
    Elapsed time is 1.208419 seconds.

Now that is really something - 12 times slowdown compared to method 1! I understand it should perform worse than method 1 because of the additional memory used for `id`, but why is it so much worse than methods 2 and 3?

Let&#39;s try to give the loops a try - as hopeless as it may sound.

    tic;
    for i=1:numel(x)
        x(i) = 5;
    end
    toc
    Elapsed time is 0.788944 seconds.

A big surprise - a loop beats a `vectorized` method 4, but is still slower than methods 1, 2 and 3. It turns out that in this particular case you can do it better:

    tic;
    for i=1:1e8
        x(i) = 6;
    end
    toc
    Elapsed time is 0.321246 seconds.

And that is the probably the most bizarre outcome of this study - **a MATLAB-written loop significantly outperforms native vector indexing**. That should certainly not be so. Note that the JIT&#39;ed loop is still 3 times slower than the theoretical peak almost obtained by method 1. So there is still plenty of room for improvement. It is just surprising (a stronger word would be more suitable) that usual &#39;vectorized&#39; indexing (`1:end`) is even slower.

**Questions**

 - is simple indexing in MATLAB **very** inefficient (methods 2, 3, and 4 are slower than method 1), or did I miss something?
 - why is method 4 **(so much) slower** than methods 2 and 3?
 - why does using `1e8` instead of `numel(x)` as a loop bound speed up the code by factor 2?

**Edit**
After reading Jonas&#39;s comment, here is another way to do that using logical indices:

    tic;
    id = logical(ones(1, 1e8));
    x(id) = 7;
    toc
    Elapsed time is 0.613363 seconds.

Much better than method 4.

For convenience:

    function test

    tic; x = zeros(1,1e8); toc

    tic; x(:) = 1; toc
    tic; x(1:end) = 2; toc
    tic; x(1:1e8) = 3; toc

    tic;
    id = 1:1e8; % colon(1,1e8);
    x(id) = 4;
    toc

    tic;
    for i=1:numel(x)
        x(i) = 5;
    end
    toc

    tic;
    for i=1:1e8
        x(i) = 6;
    end
    toc

    end

Is indexing vectors in MATLAB inefficient?

How do I make this output to a string?


    List&lt;string&gt; Client = new List&lt;string&gt;();
    foreach (string listitem in lbClients.SelectedItems)
    {
        Client.Add(listitem);
    }

Convert an array to string

I was working on a short script to change `&lt;abbr&gt;` elements&#39; inner text, but found that `nodelist` does not have a `forEach` method.  I know that `nodelist` doesn&#39;t inherit from `Array`, but doesn&#39;t it seem like `forEach` would be a useful method to have? Is there a particular implementation issue I am not aware of that prevents adding `forEach` to `nodelist`?

Note: I am aware that Dojo and jQuery both have `forEach` in some form for their nodelists.  I cannot use either due to limitations.

Why doesn&#39;t nodelist have forEach?

Hi I&#39;m Trying to merge two arrays and also want to remove duplicate values from final Array.

Here is my Array 1:

    Array
        (
        [0] =&gt; stdClass Object
        (
        [ID] =&gt; 749
        [post_author] =&gt; 1
        [post_date] =&gt; 2012-11-20 06:26:07
        [post_date_gmt] =&gt; 2012-11-20 06:26:07
    )

And this is my array 2:

    Array
    (
    [0] =&gt; stdClass Object
    (
    [ID] =&gt; 749
    [post_author] =&gt; 1
    [post_date] =&gt; 2012-11-20 06:26:07
    [post_date_gmt] =&gt; 2012-11-20 06:26:07
    
    )

I&#39;m using ``array_merge`` for merging both arrays into one array. it is giving output like this

    Array
    (
    [0] =&gt; stdClass Object
    (
    [ID] =&gt; 749
    [post_author] =&gt; 1
    [post_date] =&gt; 2012-11-20 06:26:07
    [post_date_gmt] =&gt; 2012-11-20 06:26:07
       
    [1] =&gt; stdClass Object
    (
    [ID] =&gt; 749
    [post_author] =&gt; 1
    [post_date] =&gt; 2012-11-20 06:26:07
    [post_date_gmt] =&gt; 2012-11-20 06:26:07
        
    )

I want to remove these duplicate entries or can I remove these before merging...
Pleas help.. 
Thanks!!!!!!!

PHP - Merging two arrays into one array (also Remove Duplicates)

I would like to know the following;

1. Why the given non-working example doesn&#39;t work.
2. If there are any other cleaner methods than those given in working example.

*Non-working example*

    &gt; ids=(1 2 3 4);echo ${ids[*]// /|}
    1 2 3 4
    &gt; ids=(1 2 3 4);echo ${${ids[*]}// /|}
    -bash: ${${ids[*]}// /|}: bad substitution
    &gt; ids=(1 2 3 4);echo ${&quot;${ids[*]}&quot;// /|}
    -bash: ${&quot;${ids[*]}&quot;// /|}: bad substitution

*Working example*

    &gt; ids=(1 2 3 4);id=&quot;${ids[@]}&quot;;echo ${id// /|}
    1|2|3|4
    &gt; ids=(1 2 3 4); lst=$( IFS=&#39;|&#39;; echo &quot;${ids[*]}&quot; ); echo $lst
    1|2|3|4

In context, the delimited string to be used in a [sed][1] command for further parsing.


  [1]: https://www.gnu.org/software/sed/manual/sed.html

Content Type	Original Author	Original Content on Stackoverflow
Question	Balzard	View Question on Stackoverflow
Solution 1 - Ruby	Sergio Tulentsev	View Answer on Stackoverflow
Solution 2 - Ruby	sarvavijJana	View Answer on Stackoverflow

First element of an array with condition

Ruby Problem Overview

Ruby Solutions

Solution 1 - Ruby

Solution 2 - Ruby

How to correct virtualbox installation

Meaning of ~. (tilde dot) argument?

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