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How to delete multiple values from a vector?
...match, but I'd include it for the sake of readability.
This is, btw., what setdiff does internally (but without the unique to throw away duplicates in a which are not in remove).
If remove contains incomparables, you'll have to check for them individually, e.g.
if (any (is.na (remove)))
a <- ...
Validate uniqueness of multiple columns
...kind of behaviour, one should add a unique constraint to db table. You can set it with add_index helper for one (or multiple) field(s) by running the following migration:
class AddUniqueConstraints < ActiveRecord::Migration
def change
add_index :table_name, [:field1, ... , :fieldn], unique:...
Getting the thread ID from a thread
In C# when debugging threads for example, you can see each thread's ID.
11 Answers
11
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C++ preprocessor __VA_ARGS__ number of arguments
Simple question for which I could not find answer on the net. In variadic argument macros, how to find the number of arguments? I am okay with boost preprocessor, if it has the solution.
...
How can I iterate over an enum?
...
The typical way is as follows:
enum Foo {
One,
Two,
Three,
Last
};
for ( int fooInt = One; fooInt != Last; fooInt++ )
{
Foo foo = static_cast<Foo>(fooInt);
// ...
}
Please note, the enum Last is meant to be skipped by the i...
Should a return statement be inside or outside a lock?
...
Essentially, which-ever makes the code simpler. Single point of exit is a nice ideal, but I wouldn't bend the code out of shape just to achieve it... And if the alternative is declaring a local variable (outside the lock), initializing it (inside the lock) and then returning it (outside...
Mercurial - all files that changed in a changeset?
How can you determine all the files that changed in a given changeset?
7 Answers
7
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Get average color of image via Javascript
...ltRGB;
}
height = canvas.height = imgEl.naturalHeight || imgEl.offsetHeight || imgEl.height;
width = canvas.width = imgEl.naturalWidth || imgEl.offsetWidth || imgEl.width;
context.drawImage(imgEl, 0, 0);
try {
data = context.getImageData(0, 0, width, height);
} cat...
MongoDB drop every database
I would like to know if there're a command to drop every databases from my MongoDB?
8 Answers
...
Why are function pointers and data pointers incompatible in C/C++?
...current desktop applications, but to allow it to be implemented on a large set of hardware.
It seems like the C language committee never intended void* to be a pointer to function, they just wanted a generic pointer to objects.
The C99 Rationale says:
6.3.2.3 Pointers
C has now been implem...