大约有 47,000 项符合查询结果（耗时：0.0688秒） [XML]
MongoDB SELECT COUNT GROUP BY
...
I need some extra operation based on the result of aggregate function. Finally I've found some solution for aggregate function and the operation based on the result in MongoDB. I've a collection Request with field request, source, status, requestDate.
Single Field Group By & Count:
db.Request...
Java 7 language features with Android
...u are using Android Studio, the Java 7 language should be enabled automatically without any patches. Try-with-resource requires API Level 19+, and NIO 2.0 stuff are missing.
If you can't use Java 7 features, see @Nuno's answer on how to edit your build.gradle.
The following is for historical inte...
Random string generation with upper case letters and digits
...dom.choices(string.ascii_uppercase + string.digits, k=N))
A cryptographically more secure version; see https://stackoverflow.com/a/23728630/2213647:
''.join(random.SystemRandom().choice(string.ascii_uppercase + string.digits) for _ in range(N))
In details, with a clean function for further reus...
javac not working in windows command prompt
...
ah yes, all i had to do was re-open the command prompt and it worked fine, thanks!
– Domenic
Nov 5 '09 at 6:02
1
...
How to obtain a Thread id in Python?
...
Using the logging module you can automatically add the current thread identifier in each log entry.
Just use one of these LogRecord mapping keys in your logger format string:
%(thread)d : Thread ID (if available).
%(threadName)s : Thread name (if available).
a...
Random number generation in C++11: how to generate, how does it work? [closed]
...ad about it (what is that engine , maths term like distribution , "where all integers produced are equally likely ").
2...
MySQL > Table doesn't exist. But it does (or it should)
I changed the datadir of a MySQL installation and all the bases moved correctly except for one.
I can connect and USE the database. SHOW TABLES also returns me all the tables correctly, and the files of each table exists on the MySQL data directory.
...
How to round a number to significant figures in Python
...
round_sig = lambda f,p: float(('%.' + str(p) + 'e') % f) allows you to adjust the number of significant digits!
– denizb
Aug 6 '17 at 22:43
...
What does the exclamation mark mean in a Haskell declaration?
...
It's a strictness declaration. Basically, it means that it must be evaluated to what's called "weak head normal form" when the data structure value is created. Let's look at an example, so that we can see just what this means:
data Foo = Foo Int Int !Int !(May...
What does O(log n) mean exactly?
...g that the size of the input affects the growth of the algorithm proportionally...and the same goes for, for example, quadratic time O(n2) etc..even algorithms, such as permutation generators, with O(n!) times, that grow by factorials.
...