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Count number of rows within each group
I have a dataframe and I would like to count the number of rows within each group. I reguarly use the aggregate function to sum data as follows:
...
How to implement has_many :through relationships with Mongoid and mongodb?
...ther side. For example:
class Physician
include Mongoid::Document
has_and_belongs_to_many :patients
end
class Patient
include Mongoid::Document
has_and_belongs_to_many :physicians
end
In other words you would eliminate the join table and it would have a similar effect to has_many :throug...
How to reverse a singly linked list using only two pointers?
...
Any alternative? No, this is as simple as it gets, and there's no fundamentally-different way of doing it. This algorithm is already O(n) time, and you can't get any faster than that, as you must modify every node.
It looks like your code is on the right track, but it's not...
How to Unit test with different settings in Django?
.../#overriding-settings
TestCase will have a self.settings context manager, and there will also be an @override_settings decorator that can be applied to either a test method or a whole TestCase subclass.
These features did not exist yet in Django 1.3.
If you want to change settings for all your te...
Faye vs. Socket.IO (and Juggernaut)
Socket.IO seems to be the most popular and active WebSocket emulation library. Juggernaut uses it to create a complete pub/sub system.
...
Show hide fragment in android
I am developing application which contains 2 fragments and i want to show hide according to my need. Following code has simple example of my problem.
This simple Fragmentactivity contains 1 button and one listfragment.
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Accessing an array out of bounds gives no error, why?
...defined Behavior.
There is a lot that is not specified by the language standard, for a variety of reasons. This is one of them.
In general, whenever you encounter undefined behavior, anything might happen. The application may crash, it may freeze, it may eject your CD-ROM drive or make demons com...
Does JavaScript have a built in stringbuilder class?
....
When I have to do lots of string concatenations I usually fill an array and don't use a string builder class:
var html = [];
html.push(
"<html>",
"<body>",
"bla bla bla",
"</body>",
"</html>"
);
return html.join("");
Note that the push methods accepts multiple...
Schrödingers MySQL table: exists, yet it does not
...er_table, check the data directory to make sure you have both an .frm file and .ibd file for the table in question. If it's MYISAM, there should be a .frm, .MYI and a .MYD file.
The problem can usually be resolved by deleting the orphaned file manually.
...
Cmake doesn't find Boost
...specified folder. I have specified Boost_INCLUDE_DIR , Boost_LIBRARYDIR and BOOST_ROOT , but I still get an error saying that CMake is not able to find Boost. What could be the reason of such error?
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