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Mean per group in a data.frame [duplicate]
... the many ways to specify the variables to act on. Here, vars(-Month) says all variables except Month.
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Knight's Shortest Path on Chessboard
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You have a graph here, where all available moves are connected (value=1), and unavailable moves are disconnected (value=0), the sparse matrix would be like:
(a1,b3)=1,
(a1,c2)=1,
.....
And the shortest path of two points in a graph can be found usin...
Configuring Vim for C++
... abbreviations for my C++ use, for example :
abbreviate bptr boost::shared_ptr
abbreviate cstr const std::string &
I have several functions for "code snippets" like things, for example :
function! IncludeGuard()
let basename = expand("%:t:r")
let includeGuard = '__' . basename . '_h__'
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How to perform Callbacks in Objective-C
...newer) option is to use blocks:
@interface MyClass: NSObject
{
void (^_completionHandler)(int someParameter);
}
- (void) doSomethingWithCompletionHandler:(void(^)(int))handler;
@end
@implementation MyClass
- (void) doSomethingWithCompletionHandler:(void(^)(int))handler
{
// NOTE: copyin...
Django template how to look up a dictionary value with a variable
...I find this easier to read and it avoids the need for special coding. I usually need the key and the value inside the loop anyway.
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presentViewController:animated:YES view will not appear until user taps again
...ith presentViewController:animated:completion . What I'm making is essentially a guessing game.
8 Answers
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Why should hash functions use a prime number modulus?
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Usually a simple hash function works by taking the "component parts" of the input (characters in the case of a string), and multiplying them by the powers of some constant, and adding them together in some integer type. So for e...
Select random row from a sqlite table
... the day seeded with unix epoc for today at noon so it shows the same book all day even if the query is run multiple times. Yes I know caching is more efficient for this use case just an example.
– danielson317
Apr 22 at 17:18
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How to print the full NumPy array, without truncation?
...ld instead of a.size <= _summaryThreshold, and np.nan returns False for all >/</>=/<= comparisons. 'nan' only happens to work due to fragile implementation details of Python 2's mixed-type comparison logic; it breaks completely on Python 3.
– user2357112 supports...
Time complexity of Sieve of Eratosthenes algorithm
...oose upper-bound is n(1+1/2+1/3+1/4+1/5+1/6+…1/n) (sum of reciprocals of all numbers up to n), which is O(n log n): see Harmonic number. A more proper upper-bound is n(1/2 + 1/3 + 1/5 + 1/7 + …), that is sum of reciprocals of primes up to n, which is O(n log log n). (See here or here.)
The "find...