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mongodb count num of distinct values per field/key
Is there a query for calculating how many distinct values a field contains in DB.
5 Answers
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Resolve build errors due to circular dependency amongst classes
...lasses in different header files (can happen also in the same file) . But fortunately(?) this doesn't happen often enough for me to remember the solution to this problem for the next time it happens again.
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C++代码执行安装包静默安装 - C/C++ - 清泛网 - 专注C/C++及内核技术
...。1.-----------------------CreateProcess---------------------- PROCESS_INFORMATIO...需求：安装包下载完成后，创建一个子进程自动安装。
1.-----------------------CreateProcess----------------------
PROCESS_INFORMATION pi;
STARTUPINFO si;
memset( &si, 0, ...
jQuery find events handlers registered with an object
...of jQuery 1.8, the event data is no longer available from the "public API" for data. Read this jQuery blog post. You should now use this instead:
jQuery._data( elem, "events" );
elem should be an HTML Element, not a jQuery object, or selector.
Please note, that this is an internal, 'private' s...
Comparing mongoose _id and strings
...method, if you wish to store a stringified version of the ObjectID in JSON format, or a cookie.
If you use ObjectID = require("mongodb").ObjectID (requires the mongodb-native library) you can check if results.userId is a valid identifier with results.userId instanceof ObjectID.
Etc.
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Dynamically set local variable [duplicate]
...ctionary lookups (as Sven points out in the comments there are exceptions, for example classes that define __slots__). Function locals can be optimised for speed because the compiler (usually) knows all the names in advance, so there isn't a dictionary until you call locals().
In the C implementati...
How can I link to a specific glibc version?
...blog post Linking to Older Versioned Symbols (glibc), it is possible to to force any symbol to be linked against an older one so long as it is valid by using the the same .symver pseudo-op that is used for defining versioned symbols in the first place. The following example is excerpted from the bl...
Getting visitors country from their IP
...;
if ($deep_detect) {
if (filter_var(@$_SERVER['HTTP_X_FORWARDED_FOR'], FILTER_VALIDATE_IP))
$ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
if (filter_var(@$_SERVER['HTTP_CLIENT_IP'], FILTER_VALIDATE_IP))
$ip = $_SERVER['HTTP_CLIENT_IP'];
...
Filter by property
...del.objects)
But it's better to use a list comprehension:
filtered = [x for x in MyModel.objects if x.myproperty()]
or even better, a generator expression:
filtered = (x for x in MyModel.objects if x.myproperty())
sha...
Why do people say there is modulo bias when using a random number generator?
...n 0 and RAND_MAX, which is a constant defined in cstdlib (see this article for a general overview on rand()).
Now what happens if you want to generate a random number between say 0 and 2? For the sake of explanation, let's say RAND_MAX is 10 and I decide to generate a random number between 0 and 2 ...