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What's faster, SELECT DISTINCT or GROUP BY in MySQL?
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They are essentially equivalent to each other (in fact this is how some databases implement DISTINCT under the hood).
If one of them is faster, it's going to be DISTINCT. This is because, although the two are the same, a query optimizer wo...
Using Custom Domains With IIS Express
Traditionally I use custom domains with my localhost development server. Something along the lines of:
14 Answers
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When do I really need to use atomic instead of bool? [duplicate]
...use bool is atomic by nature? I don't think it's possible to have a partially modified bool value. When do I really need to use atomic<bool> instead of bool ?
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Clang optimization levels
...ass=Arguments
As pointed out in Geoff Nixon's answer (+1), clang additionally runs some higher level optimizations, which we can retrieve with:
echo 'int;' | clang -xc -O3 - -o /dev/null -\#\#\#
Documentation of individual passes is available here.
With version 6.0 the passes are as follow...
C# LINQ find duplicates in List
...erable.GroupBy(x => x.Key).Any(g => g.Count() > 1);
Find out if all values in an enumerable are unique :
var allUnique = enumerable.GroupBy(x => x.Key).All(g => g.Count() == 1);
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How to skip over an element in .map()?
...nce it has some cost, you can use the more general .reduce(). You can generally express .map() in terms of .reduce:
someArray.map(function(element) {
return transform(element);
});
can be written as
someArray.reduce(function(result, element) {
result.push(transform(element));
return result;
}...
How does a hash table work?
... book knows the title of the book and the exact title to boot, then that's all it should take. With the title, the person, with the aid of the librarian, should be able to find the book easily and quickly.
So, how can you do that? Well, obviously you can keep some kind of list of where you put each...
C++ Singleton design pattern
... design pattern that is lazy-evaluated, guaranteed-destruction, not-technically-thread-safe:
Can any one provide me a sample of Singleton in c++?
Here is an updated C++11 implementation of the Singleton design pattern that is lazy-evaluated, correctly-destroyed, and thread-safe.
class S
{
pu...
Combine two data frames by rows (rbind) when they have different sets of columns
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@MERose Hadley: "Yes, all dplyr methods ignore rownames."
– zx8754
Dec 7 '17 at 9:11
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Search and replace in bash using regular expressions
...'s are processed in order. Also, the g flag for the expression will match all occurrences in the input.
You can also pick your favorite tool using this method, i.e. perl, awk, e.g.:
echo "$MYVAR" | perl -pe 's/[a-zA-Z]/X/g and s/[0-9]/N/g'
This may allow you to do more creative matches... For ...