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Convert data.frame columns from factors to characters
... can create a logical vector of which columns are factors, and use that to selectively apply factor
f <- sapply(bobf, class) == "factor"
bobc[,f] <- lapply(bobc[,f], factor)
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What is boxing and unboxing and what are the trade offs?
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from C# 3.0 In a Nutshell:
Boxing is the act of casting a value
type into a reference type:
int x = 9;
object o = x; // boxing the int
unboxing is... the reverse:
// unboxing o
object o = 9;
int x = (int)o;
...
new keyword in method signature
...ass.
Keep in mind that creating a "new" member is not polymorphic. If you cast the object to the base type, it will not use the derived type's member.
If you have a base class:
public class BaseClass
{
public void DoSomething() { }
}
And then the derived class:
public class DerivedType : B...
How can I convert NSDictionary to NSData and vice versa?
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For NSData -> NSDictionary, the cast to NSDictionary seems unnecessary.
– Pang
Dec 30 '15 at 8:11
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C++ templates Turing-complete?
...= config::position };
typedef typename Conditional<
static_cast<int>(GetSize<typename config::input>::value)
<= static_cast<int>(position),
AppendItem<InputBlank, typename config::input>,
Identity<typename config::input>&g...
How do I force Postgres to use a particular index?
...d, client_id, date, and description. You want to run the following query:
SELECT client_id, SUM(amount)
FROM transactions
WHERE date >= 'yesterday'::timestamp AND date < 'today'::timestamp AND
description = 'Refund'
GROUP BY client_id
PostgreSQL may choose to use the index transaction...
How to store arrays in MySQL?
... retrieve a person and all of their fruit you can do something like this:
SELECT p.*, f.*
FROM person p
INNER JOIN person_fruit pf
ON pf.person_id = p.id
INNER JOIN fruits f
ON f.fruit_name = pf.fruit_name
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How does one generate a random number in Apple's Swift language?
...nteger between 0 and n-1.
let diceRoll = Int(arc4random_uniform(6) + 1)
Cast the result to Int so you don't have to explicitly type your vars as UInt32 (which seems un-Swifty).
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Convert a string to an enum in C#
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Come on, how many of you implemented that selected answer from 2008 to only scroll down and find this is the better (modern) answer.
– TEK
Mar 18 '16 at 14:47
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Swapping two variable value without using third variable
...ks for all integer values (that includes pointers then, with some luck and casting). For the sake of completeness I would like to mention another less powerful algorithm with addition/subtraction:
A = A + B
B = A - B
A = A - B
Here you have to be careful of overflows/underflows, but otherwise it ...