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I'm trying to implement a system using node.js in which a number of sites would contain js loaded from a common host, and trigger an action when some user visits n+ sites.
I suppose a nosql solution storing a mapping of ip address => array of sites visited would be preferable to a RDBM both in terms of performance and simplicity. The actions I need are "add to array if not there already" and getting the length of the array. Also, I wouldn't like it all to sit in memory all the time, since the db might get large some day.
What's a system that fits these requirements the best? MongoDB seems like a nice option given $addToSet exists, but maybe there's something better in terms of RAM usage?
When I hear about working with lists or sets, the first choice is Redis
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What are some ways including machine learning that I can use in my projects to generate things related to another. Like related apps, related websites, related products, etc.
I've been brainstorming these are strategies...
one way i can think of is show items from same category. But that would be too broad.
2nd way improves upon previous step, it's to keep track of what people click next and promote that item. Meanwhile keep bottom list randomized to let other relevant items show up and get clicked.
3rd way is to use machine learning and provide training data somehow and use that.
I want something simple but smart, as it gets better with time.
Collaborative filtering is designed for solving exactly this problem. The problem with this approach is that produces good results having a lot of data only. I mean... A LOT. And it's not a really simple thing to use. However, any machine learning technique is not simple. There are some node.js packages for CF available, but I have no idea how good are they.
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What's better to retrieve complex data from ArangoDB: A big query with all collection joins and graph traversal or multiple queries for each piece of data?
I think it depends on several aspects, e.g. the operation(s) you want to perform, scenario in which the querie(s) should be executed or if you favor performance over maintainability.
AQL provides the ability to write a single non-trivial query which might span through entire dataset and perform complex operation(s). Dissolving a big query into multiple smaller ones might improve maintainability and code readability, but on the other hand separate queries for each piece of data might have negative performance impact in the form of network latency associated with each request. One should also consider if the scenario allows to work with partial results returned from database while the other batch of queries is being processed.
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What are applications where search techniques or more specifically planning techniques are used? I am most interested in examples in use.
I know that A* is used for path planning in Robotics, that planning is used in logistics (details would be great) but what other usages are there?
For Search in general Google, etc come to mind with their inverted indices. Again, where else is it used?
For planning examples, including logistics challenges, take a look at this list. Each use case comes with multiple datasets and a problem definition.
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Can you give several indications (pro and cons) concerning the fact to put the menus of a web application inside the database?
Mainly it depends upon your requirement of your application. Its not always a good approach to bring a drill machine to make hole in sand. Every approach has some limitations and need more efforts if you do apply some alternate approaches.
In cons you can consider
Performance ( to prepare dynamic menu every time you load the master page also the static text less time to process in compare to dynamic)
Configuration will be always an issue while adding or modifying the menu
(Always need a database guy at the time of any change)
Pros
Highly configurable and completely dynamic
Can add/remove the attribute and change the text without affecting anything in code.
We have some solutions also to overcome from the cons
In case of performance we can use caching but everytime the menu change you need to recycle the application pool.
For configuration you can provide a page to control the menu content. (No Sql guy needed)
So as I said earlier you can go either way as your application adopt easily and in much better way.
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What are the effects of multiplication of two different sound? An neither of them are constant, like two different songs, or one track of instrumental and one of vocals.
A simple Google search came up with this:
http://crca.ucsd.edu/~msp/techniques/v0.11/book-html/node77.html
Did you search for it at all?
But basically what happens is you end up creating an envelope where the second acts as a "coefficient" of sorts.
You also end up with a reduction of sound levels (since a decimal times a decimal is less both of them), so you'll need to amplify the signal a bit to retain volume.
The page I linked gives a lot more explanation and has a lot of the algebra needed to write up a code to implement it. Look there if you have any more questions.