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data.table vs dplyr: can one do something well the other can't or does poorly?
...z=sum(z) * mul), by = .EACHI]
What is the advantage?
We don't have to allocate memory for the intermediate result.
We don't have to group/hash twice (one for aggregation and other for joining).
And more importantly, the operation what we wanted to perform is clear by looking at j in (2).
Chec...
How do you add an in-app purchase to an iOS application?
... product
SKProductsRequest *productsRequest = [[SKProductsRequest alloc] initWithProductIdentifiers:[NSSet setWithObject:kRemoveAdsProductIdentifier]];
productsRequest.delegate = self;
[productsRequest start];
}
else{
NSLog(@"User cannot make payments du...
Why does modern Perl avoid UTF-8 by default?
...lem
When you read data into Perl, it doesn't care what encoding it is. It allocates some memory and stashes the bytes away there. If you say print $str, it just blits those bytes out to your terminal, which is probably set to assume everything that is written to it is UTF-8, and your text shows up....
What is a NullReferenceException, and how do I fix it?
...le = new Person[5];
people[0].Age = 20 // people[0] is null. The array was allocated but not
// initialized. There is no Person to set the Age for.
Jagged Arrays
long[][] array = new long[1][];
array[0][0] = 3; // is null because only the first dimension is yet initialized.
...
Window Features - 更多技术 - 清泛网 - 专注C/C++及内核技术
...ata associated with the window, and it should release any system resources allocated for the window. If the application does not release the resources, the system will free any resources not freed by the application.
Destroying a window does not affect the window class from which the window is crea...
MFC Grid control 2.27 - C/C++ - 清泛网 - 专注IT技能提升
...y. Each cell holds a pointer to a font structure, and this pointer is only allocated and used if you set that cell's font to a non-default value.
The grid also has a virtual mode that stops the grid from actually creating cells, and allows you to specify either a callback funtion or message handler...
MFC Grid control 2.27 - C/C++ - 清泛网 - 专注IT技能提升
...y. Each cell holds a pointer to a font structure, and this pointer is only allocated and used if you set that cell's font to a non-default value.
The grid also has a virtual mode that stops the grid from actually creating cells, and allows you to specify either a callback funtion or message handler...
MFC Grid control 2.27 - C/C++ - 清泛网 - 专注IT技能提升
...y. Each cell holds a pointer to a font structure, and this pointer is only allocated and used if you set that cell's font to a non-default value.
The grid also has a virtual mode that stops the grid from actually creating cells, and allows you to specify either a callback funtion or message handler...
MFC Grid control 2.27 - C/C++ - 清泛网 - 专注IT技能提升
...y. Each cell holds a pointer to a font structure, and this pointer is only allocated and used if you set that cell's font to a non-default value.
The grid also has a virtual mode that stops the grid from actually creating cells, and allows you to specify either a callback funtion or message handler...
MFC Grid control 2.27 - C/C++ - 清泛网 - 专注IT技能提升
...y. Each cell holds a pointer to a font structure, and this pointer is only allocated and used if you set that cell's font to a non-default value.
The grid also has a virtual mode that stops the grid from actually creating cells, and allows you to specify either a callback funtion or message handler...