Mongo 2.0 added an $and operator, so you can do a query like this:

    db.things.find({$and: [{$or : [{&#39;a&#39;:1},{&#39;b&#39;:2}]},{$or : [{&#39;a&#39;:2},{&#39;b&#39;:3}]}] })

http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24and

For multiple like in sql we use $in and for not we use $nin 
vc is our collection name here.We are finding those string contains cpu or memo.

    db.collection(&#39;vc&#39;).find({   &quot;name&quot; :   { $in: [ /cpu/, /memo/ ]   }     }

You can not nest multiple $or statements. 

This is documented here:

http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24or

Apart from that: your query does make much sense. 

If you are trying to query for **a** being either 2 or 3 and **b** being either 5 or 4: 

{a : {$in : [2,3]}, b: {$in : [4,5 ]} }

Please don&#39;t try to invent new syntax.

$and will not do the job, since the 2nd $or will not validate if the first one fails. 

From the Mongo man page:

*The $and operator uses short-circuit evaluation. If the first expression (e.g. &lt;expression1&gt;) evaluates to false, MongoDB will not evaluate the remaining expressions.*

Nested $or however should do the trick:

db.things.find({$or: [{$or : [{&#39;a&#39;:1},{&#39;b&#39;:2}]},{$or : [{&#39;a&#39;:2},{&#39;b&#39;:3}]}] })

What is the alternative to `\n` (for new line) in a `MsgBox()`?


How to use \n new line in VB msgbox() ...?

When building a model in R, how do you save the model specifications such that you can reuse it on new data?  Let&#39;s say I build a logistic regression on historical data but won&#39;t have new observations until next month.  What&#39;s the best approach?

Things that I have considered:

 - Saving the model object and loading in a new session
 - I know that some models can be exported with PMML, but haven&#39;t really seen anything about importing PMML

Simply, I am trying to get a sense of what you do when you need to use your model in a new session.

Thanks in advance.



Reusing a Model Built in R

How would I have multiple $or operations? So far I&#39;ve tried the following but it silently ignores the 2nd $or. 

    {
      $or: [{a: 2}, {a: 3}], 
      $or: [{b: 5}, {b: 4}]
    }

I assume this is because I&#39;m using two identical keys. Is there any way around this?


MongoDB - Multiple $or operations

How would I have multiple $or operations? So far I've tried the following but it silently ignores the 2nd $or.
<pre><code class="hljs language-css">{
 $or: [{a: 2}, {a: 3}], 
 $or: [{b: 5}, {b: 4}]
}
</code></pre>
I assume this is because I'm using two identical keys. Is there any way around this?

SQL keys, MUL vs PRI vs UNI

I would like to print a specific Python dictionary key:

```
mydic = {}
mydic[&#39;key_name&#39;] = &#39;value_name&#39;
```
    
Now I can check if `mydic.has_key(&#39;key_name&#39;)`, but what I would like to do is print the name of the key `&#39;key_name&#39;`. Of course I could use `mydic.items()`, but I don&#39;t want **all** the keys listed, merely one specific key. For instance I&#39;d expect something like this (in pseudo-code):

```
print &quot;the key name is&quot;, mydic[&#39;key_name&#39;].name_the_key(), &quot;and its value is&quot;, mydic[&#39;key_name&#39;]
```

Is there any `name_the_key()` method to print a key name?


----------


**Edit:**
OK, thanks a lot guys for your reactions! :) I realise my question is not well formulated and trivial. I just got confused because I realised `&#39;key_name&#39;` and `mydic[&#39;key_name&#39;]` are two different things and I thought it would be incorrect to print the `&#39;key_name&#39;` out of the dictionary context. But indeed I can simply use the `&#39;key_name&#39;` to refer to the key! :)



How to print a dictionary&#39;s key?

How can I get the **highest** `key/index` in an array with [tag:PHP]? I know how to do it for the values.

E.g.: from this array I would like to get `10` as an `integer` value:

```php
$arr = array(1 =&gt; &quot;A&quot;, 10 =&gt; &quot;B&quot;, 5 =&gt; &quot;C&quot;);
```

I know how I could code it but I was asking myself if there is a function for this as well.

Search for highest key/index in an array

I need a way to get a dictionary value if its key exists, or simply return `None`, if it does not.

However, Python raises a `KeyError` exception if you search for a key that does not exist. I know that I can check for the key, but I am looking for something more explicit. Is there a way to just return `None` if the key does not exist?

Return a default value if a dictionary key is not available

I want to map objects of a given class to objects of another. The class I want to use as key, however, was not written by me and is a simple `struct` with a few values. std::map orders it&#39;s contents, and I was wondering how it does it, and if any arbitrary class can be used as a key or if there&#39;s a set of requirements (operators and what not) that need to be defined.

If so, I could create a wrapper for the class implementing the operators map uses. I just need to know what I need to implement first, and none of the references for the class I [found online][1] specify them.


  [1]: http://en.cppreference.com/w/cpp/container/map

What requirements must std::map key classes meet to be valid keys?

I am working on a project in which I am tracking number of clicks on a topic.

I am using mongodb and I have to group number of click by date( i want to group data for 15 days).


I am having data store in following format in mongodb

    { 
       &quot;_id&quot; : ObjectId(&quot;4d663451d1e7242c4b68e000&quot;), 
      &quot;date&quot; : &quot;Mon Dec 27 2010 18:51:22 GMT+0000 (UTC)&quot;, 
      &quot;topic&quot; : &quot;abc&quot;, 
      &quot;time&quot; : &quot;18:51:22&quot;
    }
    { 
        &quot;_id&quot; : ObjectId(&quot;4d6634514cb5cb2c4b69e000&quot;), 
        &quot;date&quot; : &quot;Mon Dec 27 2010 18:51:23 GMT+0000 (UTC)&quot;, 
        &quot;topic&quot; : &quot;bce&quot;, 
        &quot;time&quot; : &quot;18:51:23&quot;
    }


i want to group number of clicks on topic:abc by days(for 15 days)..i know how to group that but how can I group by date which are stored in my database

I am looking for result in following format

    [
      {
        &quot;date&quot; : &quot;date in log&quot;,
        &quot;click&quot; : 9 
      },  
      {
        &quot;date&quot; : &quot;date in log&quot;,
        &quot;click&quot; : 19
      },  
    ]

I have written code but it will work only if date are in string (code is here http://pastebin.com/2wm1n1ix)
...please guide me how do I group it


group by dates in mongodb 

I was showing my co-worker performance benchmarks of MongoDB vs SQL 2008 and while he believes MongoDB is faster, he doesn&#39;t understand how its possible. His logic, was that SQL has been around for decades, and has some of the smartest people working on it, and how can MongoDB; a relatively new kid on the block be so superior in performance? I wasn&#39;t able to really provide a solid and technical answer, and I was hoping you guys could assist.



Why Is MongoDB So Fast

I have a document structure something along the lines of the following:

&lt;!-- language: lang-js --&gt;

    {
    &quot;_id&quot; : &quot;777&quot;,
    &quot;someKey&quot; : &quot;someValue&quot;,
    &quot;someArray&quot; : [
		{
			&quot;name&quot; : &quot;name1&quot;,
			&quot;someNestedArray&quot; : [
				{
					&quot;name&quot; : &quot;value&quot;
				},
				{
					&quot;name&quot; : &quot;delete me&quot;
				}
			]
		}
	  ]
    }

I want to delete the nested array element with the value &quot;delete me&quot;.

I know I can find documents which match this description using nested $elemMatch expressions. What is the query syntax for removing the element in question? 

How to remove an element from a doubly-nested array in a MongoDB document.

Could anybody tell me what is the pros and cons of mongodb, especially comparing with the relational database? including ACID, scalability, throughput, main memory usage, insert/query performance and index size etc.

Pros and cons of MongoDB?

It&#39;s widely mentioned that Redis is &quot;Blazing Fast&quot; and mongoDB is fast too. But, I&#39;m having trouble finding actual numbers comparing the results of the two. Given similar configurations, features and operations (and maybe showing how the factor changes with different configurations and operations), etc, is Redis 10x faster?, 2x faster?, 5x faster?

I&#39;m ONLY speaking of performance. I understand that mongoDB is a different tool and has a richer feature set.  This is not the &quot;Is mongoDB *better* than Redis&quot; debate. I&#39;m asking, by what margin does Redis outperform mongoDB?

At this point, even cheap benchmarks are better than no benchmarks.

Content Type	Original Author	Original Content on Stackoverflow
Question	Mike Neumegen	View Question on Stackoverflow
Solution 1 - Key	Nader	View Answer on Stackoverflow
Solution 2 - Key	Gajender Singh	View Answer on Stackoverflow
Solution 3 - Key	Andreas Jung	View Answer on Stackoverflow
Solution 4 - Key	user1231157	View Answer on Stackoverflow

MongoDB - Multiple $or operations

Key Problem Overview

Key Solutions

Solution 1 - Key

Solution 2 - Key

Solution 3 - Key

Solution 4 - Key

Reusing a Model Built in R

How to use \n new line in VB msgbox() ...?

Attributions