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How to sum a variable by group
...
Using aggregate:
aggregate(x$Frequency, by=list(Category=x$Category), FUN=sum)
Category x
1 First 30
2 Second 5
3 Third 34
In the example above, multiple dimensions can be specified in the list. Multiple aggregated metrics of the same data type can be incorporated via cbind:
ag...
create a trusted self-signed SSL cert for localhost (for use with Express/Node)
...y. we will work inside it.
Step 2. create a request config file named req.cnf with the following content (credit goes to: @Anshul)
req.cnf :
[req]
distinguished_name = req_distinguished_name
x509_extensions = v3_req
prompt = no
[req_distinguished_name]
C = Country initials like US, RO, GE
ST = St...
How does the “this” keyword work?
...t("I'm evaluated in the initial global execution context!");
setTimeout(function () {
alert("I'm NOT evaluated in the initial global execution context.");
}, 1);
</script>
When evaluating code in the initial global execution context, ThisBinding is set to the global object, window ...
Undefined, unspecified and implementation-defined behavior
...tandard as unspecified (for example, order of evaluation of arguments to a function). Where possible, this International Standard defines a set of allowable behaviors. These define the nondeterministic aspects of the abstract machine.
Certain other operations are described in this International Stan...
C++STL容器使用经验总结 - C/C++ - 清泛网 - 专注C/C++及内核技术
...ack(RCSPW(new Widget));
...
v.erase(remove_if(v.begin(),v.end(),not1(mem_fun(&Widget::isCertified))),v.end());
第34条：了解哪些算法要求使用排序的区间作为参数。
下面的代码要求排序的区间：
binary_search lower_bound
upper_bound equal_range
set_union set_...
select、poll、epoll之间的区别总结[整理] - C/C++ - 清泛网 - 专注C/C++及内核技术
...echo程序进行了测试。连接如下所示：
select：http://www.cnblogs.com/Anker/archive/2013/08/14/3258674.html
poll：http://www.cnblogs.com/Anker/archive/2013/08/15/3261006.html
epoll：http://www.cnblogs.com/Anker/archive/2013/08/17/3263780.html
今天对这三种IO多路复用进...
Trusting all certificates with okHttp
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Update OkHttp 3.0, the getAcceptedIssuers() function must return an empty array instead of null.
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Regular expression to match standard 10 digit phone number
...^(\+\d{1,2}\s)?\(?\d{3}\)?[\s.-]\d{3}[\s.-]\d{4}$
Matches the following
123-456-7890
(123) 456-7890
123 456 7890
123.456.7890
+91 (123) 456-7890
If you do not want a match on non-US numbers use
^(\+0?1\s)?\(?\d{3}\)?[\s.-]\d{3}[\s.-]\d{4}$
Update :
As noticed by user Simon Weaver below, if y...
Decorators with parameters?
...rguments is a bit different - the decorator with arguments should return a function that will take a function and return another function. So it should really return a normal decorator. A bit confusing, right? What I mean is:
def decorator_factory(argument):
def decorator(function):
def...
What is lexical scope?
...
First, lexical scope (also called static scope), in C-like syntax:
void fun()
{
int x = 5;
void fun2()
{
printf("%d", x);
}
}
Every inner level can access its outer levels.
There is another way, called dynamic scope used by the first implementation of Lisp, again in a ...