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What is an idempotent operation?
...ng, an idempotent operation is one that has no additional effect if it is called more than once with the same input parameters. For example, removing an item from a set can be considered an idempotent operation on the set.
In mathematics, an idempotent operation is one where f(f(x)) = f(x). For exa...
Warning message: In `…` : invalid factor level, NA generated
...
Here is a flexible approach, it can be used in all cases, in particular:
to affect only one column, or
the dataframe has been obtained from applying previous operations (e.g. not immediately opening a file, or creating a new data frame).
First, un-factorize a stri...
How to get an array of specific “key” in multidimensional array without looping
...s = array_map(function ($ar) {return $ar['id'];}, $users);
Before(Technically php 4.0.6+), you must create an anonymous function with create_function instead:
$ids = array_map(create_function('$ar', 'return $ar["id"];'), $users);
...
How to do a JUnit assert on a message in a logger
I have some code-under-test that calls on a Java logger to report its status.
In the JUnit test code, I would like to verify that the correct log entry was made in this logger. Something along the following lines:
...
Fluent Validation vs. Data Annotations [closed]
...when used for ASP.NET MVC validatation? They seem to have similar objects, all the way to their object names. Is one related to another? What are their differences? In what way do these differences denote different use cases?
...
Most efficient conversion of ResultSet to JSON?
...tests. You could probably make it more elegant with a HashMap lookup to a callback but I doubt it would be any faster. As to memory, this is pretty slim as is.
Somehow I doubt this code is actually a critical bottle neck for memory or performance. Do you have any real reason to try to optimize it?...
Auto-expanding layout with Qt-Designer
... QVBoxLayout should now stretch to fit the window and will resize automatically when the entire window is resized.
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What are the rules for JavaScript's automatic semicolon insertion (ASI)?
...
First of all you should know which statements are affected by the automatic semicolon insertion (also known as ASI for brevity):
empty statement
var statement
expression statement
do-while statement
continue statement
break statement...
How to create GUID / UUID?
I'm trying to create globally-unique identifiers in JavaScript. I'm not sure what routines are available on all browsers, how "random" and seeded the built-in random number generator is, etc.
...
get keys of json-object in JavaScript [duplicate]
...t.keys function to get an array of the keys (property names) in an object. All modern browsers have Object.keys (including IE9+).
Object.keys(jsonData).forEach(function(key) {
var value = jsonData[key];
// ...
});
The rest of this answer was written in 2011. In today's world, A) You don...