大约有 40,000 项符合查询结果（耗时：0.0236秒） [XML]
ObservableCollection Doesn't support AddRange method, so I get notified for each item added, besides
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Scott Dorman is correct. Calling the built-in Add method will trigger something like 3 events per add (a NotifyPropertyChange for item count, NotifyPropertyChange for item indexing[] and an NotifyCollectionChanged event for the item added). To get the...
Select distinct values from a table field
...ant any ordering to be applied to a query, not even the default ordering, call order_by() with no parameters.
and distinct() in the note where it discusses issues with using distinct() with ordering.
To query your DB, you just have to call:
models.Shop.objects.order_by().values('city').distinct(...
How to optimize for-comprehensions and loops in Scala?
...s Java. I'm revisiting some Project Euler problems in Scala that I originally tackled in Java. Specifically Problem 5: "What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?"
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How to create streams from string in Node.Js?
...g"])
readable.on("data", (chunk) => {
console.log(chunk) // will be called once with `"input string"`
})
Note that at least between 10.17 and 12.3, a string is itself a iterable, so Readable.from("input string") will work, but emit one event per character. Readable.from(["input string"]) wil...
Cost of len() function
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Calling len() on those data types is O(1) in CPython, the most common implementation of the Python language. Here's a link to a table that provides the algorithmic complexity of many different functions in CPython:
TimeComple...
Collect successive pairs from a stream
...eamEx library which extends standard streams provides a pairMap method for all stream types. For primitive streams it does not change the stream type, but can be used to make some calculations. Most common usage is to calculate differences:
int[] pairwiseDiffs = IntStreamEx.of(input).pairMap((a, b)...
What does T&& (double ampersand) mean in C++11?
...e in the draft C++11 standard, but are not true for the final one! Specifically, it says at various points that rvalue references can bind to lvalues, which was once true, but was changed.(e.g. int x; int &&rrx = x; no longer compiles in GCC) – drewbarbs Jul 13 '14 at 16:12
The biggest d...
Change all files and folders permissions of a directory to 644/755
How would I change all files to 644 and all folders to 755 using chmod from the linux command prompt? (Terminal)
8 Answ...
Why is sed not recognizing \t as a tab?
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Not all versions of sed understand \t. Just insert a literal tab instead (press Ctrl-V then Tab).
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Real life example, when to use OUTER / CROSS APPLY in SQL
... ORDER BY pr.name) pa
ORDER BY pr.name,
pa.name
2) Calling a Table Valued Function for each row in the outer query
SELECT *
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_query_plan(qs.plan_handle)
3) Reusing a column alias
SELECT number,
doubled_number...