 - The opposite of `reject` is `select` (returning a new array)
 - The opposite of `reject!` is `select!` (editing the array in place)
 - The opposite of `keep_if` is `delete_if` (editing the array in place)

I think it has to do with well thought-out semantics, and I&#39;d argue that it is correct.  Let&#39;s say you already have a set of things, &quot;t1, t2, and t3&quot;; if you reject a subset, you say &quot;I reject t1 and t2&quot;.  You don&#39;t mention t3, because it is not affected by your action (your rejection): the default is &quot;keep&quot;.  But if you are expressing what you intend to keep, and you just say &quot;I keep t1 and t2&quot;, the status of t3 is called into question: after all, you already have t1 and t2, so what&#39;s the point of saying you&#39;re keeping them (they are already in the default state, &quot;keep&quot;), especially since you&#39;re implicitly also keeping t3.  By using the syntax &quot;keep_if&quot;, you are explicitly indicating that there is a condition (simple or compound) which will determine what is to be kept and what is to be discarded.

In my application I load text files that are structured as follows:

- First non numeric column (ID)
- A number of non-numeric columns (strings)
- A number of numeric columns (floats)

The number of the non-numeric columns is variable. Currently I load the data into a DataFrame like this:

    source = pandas.read_table(inputfile, index_col=0)

I would like to drop all non-numeric columns in one fell swoop, without knowing their names or indices, since this could be doable reading their dtype. Is this possible with pandas or do I have to cook up something on my own?

Drop non-numeric columns from a pandas DataFrame

I&#39;m working with SQL Server 2008 and I can&#39;t seem to do drop and create a database.

I&#39;ve tried a few different ways but I always end up failing to drop or trying to &quot;use&quot; before it seems to be created.

My current attempt looks like this.

    use master;
    GO
    IF EXISTS (SELECT name FROM master.dbo.sysdatabases WHERE name = N&#39;test&#39;)
    BEGIN
    DROP DATABASE [test];
    END
    GO
    CREATE DATABASE [test];
    GO
    use [test];
    GO
    
The `GO` were suggested on a MS forum as a way to stop some issues that occur when selecting databases.

With this I currently get the output (with a ore existing database of the same name) of:

&gt; Msg 3702, Level 16, State 4, Line 3  
&gt; Cannot drop database &quot;test&quot; because it is currently in use.  
&gt; Msg 1801, Level 16, State 3, Line 1  
&gt; Database &#39;test&#39; already exists. Choose a different database name.  
&gt; Msg 2714, Level 16, State 6, Line 2  
&gt; There is already an object named &#39;staff_type&#39; in the database.

With the last 2 lines repeated for every table in my database.

unable to drop and create database in sql server

Is seems that it might be `keep_if`.

If so, why isn&#39;t it called `keep`?

What is the opposite of Array#reject in ruby?

<p>Is seems that it might be <code>keep_if</code>.</p>
<p>If so, why isn't it called <code>keep</code>?</p>


I&#39;m using JPEGCAM to allow users to take a profile pic with their web cam. This uploads a temporary file as so:


    def ajax_photo_upload    
      File.open(upload_path, &#39;w:ASCII-8BIT&#39;) do |f|
        f.write request.raw_post
      end
      # @user.photo = File.open(upload_path)
      @user.assign_attributes(
        :photo =&gt; File.open(upload_path),
        :orig_filename =&gt; &quot;#{current_user.full_name}.jpg&quot;
      )
      if @user.save
      respond_to do |format|
      .....
    private
    
      def upload_path # is used in upload and create
        file_name = session[:session_id].to_s + &#39;.jpg&#39;
        File.join(::Rails.root.to_s, &#39;public&#39;, &#39;temp&#39;, file_name)
      end

What&#39;s the best way to go about deleting this temporary file safely? Thanks

Rails how to delete a file without failing on error

I have an array: 

    [1,2,3,4,5,6,7,8,9,0] 

that I&#39;d like to iterate 3 at a time, which produces

    1,2,3  and  4,5,6  and  7,8,9   and   0

What&#39;s the best way to do this in Ruby?

Iterate an array, n items at a time

I&#39;m trying to get the first key and value key from a hash table in ruby. I don&#39;t know the key values of the hash because it is passed to the method. I cant find anywhere online how to find the first key/value as a separate hash table. 
I think `hash[0]` will just try to find an element with a name 0 it just returns `nil` when I run the code. 

I know I can find the key name and the value and then create a new hash from them but i wonder if there is an easier way to do this so I get a hash right away. 

here is my code: 

    def rps_game_winner(game)
    
    rock_in_hash = game.invert[&#39;R&#39;]
    paper_in_hash = game.invert[&#39;P&#39;]
    scissors_in_hash = game.invert[&#39;S&#39;]
    
    if(rock_in_hash)
          if(paper_in_hash)
        	return paper_in_hash;
          elsif(scissors_in_hash)
        	return rock_in_hash
          end
        elsif(paper_in_hash)
          if(rock_in_hash)
        	return paper_in_hash
          elsif(scissors_in_hash)
        	return scissors_in_hash
          end
        end
        	key = game.keys[-1]
         	value = game.values[-1]
    	    	winner = {key =&gt; value}
        return winner 
        end

    game_one = { &quot;Bob&quot; =&gt; &#39;P&#39;, &quot;Jim&quot; =&gt; &#39;P&#39; }
    
    puts rps_game_winner(game_one)

This gets me the correct result the problem is I don&#39;t understand why it&#39;s -1 instead of zero...
And i was hoping there was a better way to get the first key/value pair of a hash table instead of creating new hash table with the key and value you retrieved from the previous table. 

How to get the first key and value pair from a hash table in Ruby

I want to display a label in `form_for`:

    &lt;div class=&quot;field&quot;&gt;
      &lt;%= f.label :name %&gt;&lt;br /&gt;
      &lt;%= f.text_field :name %&gt;
    &lt;/div&gt;

This generates the label &quot;Name&quot;, but I want it to be &quot;Your Name&quot;. How can I change it?

Rails: Custom text for rails form_for label

I have a bunch of code to look at, and now it is debugging time. Since I have never been a fan of Ruby&#39;s debugger I am looking for a way of going through code and reading it.

What I am trying to do is get the location of the file where a loaded class is defined:

    Foo::Bar.create(:param) # how can I know file location in runtime?

For smaller, better organized, projects, I would just search for `class Bar` but here that is not possible since there are many classes named `Bar`, and, to make matters worse, some of them are under the same namespace. I know, it&#39;s trouble waiting to happen.

Note: I&#39;m using Ruby 1.8.7.



Get class location from class object


    array=(a b c d)
I would like to add a character before each element of the array in order to have this

    array=(^a ^b ^c ^d)
An easy way to do that is to loop on array elements and change values one by one

    for i in &quot;${#array[@]}&quot;
    do
        array[i]=&quot;^&quot;array[i]
    done
But I would like to know if there is any way to do the same thing without looping on the array as I have to do the same instruction on all elements.

Thanks in advance.


How to change values of bash array elements without loop

I am trying to do the following but with numpy arrays:

    x = [(0.1, 1.), (0.1, 2.), (0.1, 3.), (0.1, 4.), (0.1, 5.)]
    normal_result = zip(*x)

This should give a result of:

    normal_result = [(0.1, 0.1, 0.1, 0.1, 0.1), (1., 2., 3., 4., 5.)]

But if the input vector is a numpy array:

    y = np.array(x)
    numpy_result = zip(*y)
    print type(numpy_result)

It (expectedly) returns a:

    &lt;type &#39;list&#39;&gt;

The issue is that I will need to transform the result back into a numpy array after this.

**What I would like to know is what is if there is an efficient numpy function that will avoid these back-and-forth transformations?**

What is the equivalent of &quot;zip()&quot; in Python&#39;s numpy?

Arrays are not a [primitive type](http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html) in Java, but they [are not objects either](https://stackoverflow.com/questions/5564423/arrays-in-java-and-how-they-are-stored-in-memory), so are they passed by value or by reference? Does it depend on what the array contains, for example references or a primitive type?

Are arrays passed by value or passed by reference in Java?

### What is this?

This is a number of answers about warnings, errors, and notices you might encounter while programming PHP and have no clue how to fix them. This is also a Community Wiki, so everyone is invited to participate adding to and maintaining this list.

### Why is this?

Questions like [&quot;Headers already sent&quot;](https://stackoverflow.com/a/12770075) or [&quot;Calling a member of a non-object&quot;](https://stackoverflow.com/a/12769983) pop up frequently on Stack Overflow. The root cause of those questions is always the same. So the answers to those questions typically repeat them and then show the OP which line to change in their particular case. These answers do not add any value to the site because they only apply to the OP&#39;s particular code. Other users having the same error cannot easily read the solution out of it because they are too localized. That is sad because once you understood the root cause, fixing the error is trivial. Hence, this list tries to explain the solution in a general way to apply.

### What should I do here?

If your question has been marked as a duplicate of this one, please find your error message below and apply the fix to your code. The answers usually contain further links to investigate in case it shouldn&#39;t be clear from the general answer alone.

If you want to contribute, please add your &quot;favorite&quot; error message, warning or notice, one per answer, a short description what it means (even if it is only highlighting terms to their manual page), a possible solution or debugging approach and a listing of existing Q&amp;A that are of value. Also, feel free to improve any existing answers.

## The List

 * [Nothing is seen. The page is empty and white.](https://stackoverflow.com/a/12772851) (also known as *White Page/Screen Of Death*)
 * [Code doesn&#39;t run/what looks like parts of my PHP code are output](https://stackoverflow.com/a/24423272)
 * [Warning: Cannot modify header information - headers already sent](https://stackoverflow.com/a/12770075)
 * [Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given](https://stackoverflow.com/a/12770072) a.k.a.  
   [Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource](https://stackoverflow.com/a/12770072)
 * [Warning: *[function]* expects parameter 1 to be resource, boolean given](https://stackoverflow.com/a/14067623)
 * [Warning: *[function]*: failed to open stream: *[reason]*](https://stackoverflow.com/a/12820243)
 * [Warning: open_basedir restriction in effect](https://stackoverflow.com/a/12772244)
 * [Warning: Division by zero](https://stackoverflow.com/a/21507314)
 * [Warning: Illegal string offset &#39;XXX&#39;](https://stackoverflow.com/a/27678436)
 * [Warning: count(): Parameter must be an array or an object that implements Countable](https://stackoverflow.com/a/56011600)
 * [Parse error: syntax error, unexpected &#39;\[&#39;](https://stackoverflow.com/a/22316776)
 * [Parse error: syntax error, unexpected T_XXX](https://stackoverflow.com/a/12770089)
 * [Parse error:  syntax error, unexpected T_ENCAPSED_AND_WHITESPACE](https://stackoverflow.com/a/13935532)
 * [Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM](https://stackoverflow.com/a/12770129)
 * [Parse error: syntax error, unexpected &#39;require_once&#39; (T_REQUIRE_ONCE), expecting function (T_FUNCTION)](https://stackoverflow.com/q/23726288)
 * [Parse error: syntax error, unexpected T_VARIABLE](https://stackoverflow.com/a/15539535)
 * [Fatal error: Allowed memory size of XXX bytes exhausted (tried to allocate XXX bytes)](https://stackoverflow.com/a/12770179)
 * [Fatal error: Call to a member function ... on a non-object or null](https://stackoverflow.com/a/12769983)
 * [Fatal Error: Call to Undefined function XXX](https://stackoverflow.com/a/12784048)
 * [Fatal Error: Cannot redeclare XXX](https://stackoverflow.com/a/13879461)
 * [Fatal error: Can&#39;t use function return value in write context](https://stackoverflow.com/a/12770530)
 * [Fatal error: Declaration of AAA::BBB() must be compatible with that of CCC::BBB()](https://stackoverflow.com/q/1885302)&#39;
 * [Return type of AAA::BBB() should either be compatible with CCC::BBB(), or the #[\ReturnTypeWillChange] attribute should be used](https://stackoverflow.com/q/71133749)
 * [Fatal error: Using $this when not in object context](https://stackoverflow.com/a/12770317)
 * [Fatal error: Object of class Closure could not be converted to string](https://stackoverflow.com/a/56658110)
 * [Fatal error: Undefined class constant](https://stackoverflow.com/a/59619392/1255289)
 * [Fatal error: Uncaught TypeError: Argument #n must be of type x, y given](https://stackoverflow.com/a/67781316)
 * [Notice: Array to string conversion](https://stackoverflow.com/a/24507107)
 * [Notice: Trying to get property of non-object error](https://stackoverflow.com/a/26572398)
 * [Notice: Undefined variable or property](https://stackoverflow.com/a/12778634)
 * [&quot;Notice: Undefined Index&quot;, or &quot;Warning: Undefined array key&quot;](https://stackoverflow.com/a/12770836)
 * [Notice: Undefined offset XXX](https://stackoverflow.com/a/21793407) [Reference]
 * [Notice: Uninitialized string offset: XXX](https://stackoverflow.com/a/17630869)
 * [Notice: Use of undefined constant XXX - assumed &#39;XXX&#39; / Error: Undefined constant XXX](https://stackoverflow.com/a/12773272)
 * [MySQL: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ... at line ...](https://stackoverflow.com/a/12771239)
 * [Strict Standards: Non-static method *[&amp;lt;class&gt;::&amp;lt;method&gt;]* should not be called statically](https://stackoverflow.com/a/21942832)
 * [Warning: function expects parameter X to be boolean/string/integer](https://stackoverflow.com/a/52771226)
 * [HTTP Error 500 - Internal server error](https://stackoverflow.com/a/53843354)
 * [Deprecated: Arrays and strings offset access syntax with curly braces is deprecated](https://stackoverflow.com/a/59158847)


Also, see:

- [Reference - What does this symbol mean in PHP?](https://stackoverflow.com/q/3737139)

Reference - What does this error mean in PHP?

The question is basically self-explanatory.  I haven&#39;t been able to find an API for arrays (other than this [Arrays](http://docs.oracle.com/javase/6/docs/api/java/util/Arrays.html), but this just defines a bunch of static helper functions for dealing with actual arrays).  If there is no class for it, this seems to suggest that an array can&#39;t be an `Object`.

However, the fact that an array has public fields like `length` and methods that it can invoke like `.equals()` and `.clone()` seem to suggest (very strongly) the complete opposite.

What is the explanation for the odd presentation and behavior of primitive arrays?

As a note, I tried to use the &quot;Open Implementation&quot; Eclipse feature on the `.clone()` method of an array just now, hoping that I would be able to look at where and how this method was defined (since it said int[] overrode it from Object), but it actually caused my entire Eclipse to freeze up and crash...

Content Type	Original Author	Original Content on Stackoverflow
Question	B Seven	View Question on Stackoverflow
Solution 1 - Ruby	pguardiario	View Answer on Stackoverflow
Solution 2 - Ruby	davej	View Answer on Stackoverflow

What is the opposite of Array#reject in ruby?

Ruby Problem Overview

Ruby Solutions

Solution 1 - Ruby

Solution 2 - Ruby

unable to drop and create database in sql server

Drop non-numeric columns from a pandas DataFrame

Attributions