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data.table vs dplyr: can one do something well the other can't or does poorly?
... remember is for it to return a list so that each element of the list gets converted to a column.
In dplyr, cannot do that. Have to resort to do() depending on how sure you are as to whether your function would always return a single value. And it is quite slow.
Once again, data.table's synta...
Reading output of a command into an array in Bash
I need to read the output of a command in my script into an array. The command is, for example:
3 Answers
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stringstream, string, and char* conversion confusion
... object that's destroyed at the end of the full expression. If you get a pointer to a C string from that (stringstream.str().c_str()), it will point to a string which is deleted where the statement ends. That's why your code prints garbage.
You could copy that temporary string object to some ot...
What are the use cases for selecting CHAR over VARCHAR in SQL?
...1 byte of overhead needed to indicate length or EOL on a VARCHAR.
As was pointed out by Gaven in the comments: Things change when it comes to multi-byte characters sets, and is a is case where VARCHAR becomes a much better choice.
A note about the declared length of the VARCHAR: Because it stores th...
What is the meaning of the term arena in relation to memory?
...f that memory. For example:
char * arena = malloc(HUGE_NUMBER);
unsigned int current = 0;
void * my_malloc(size_t n) { current += n; return arena + current - n; }
The point is that you get full control over how the memory allocation works. The only thing outside your control is the single libra...
How to determine if a number is a prime with regex?
... String s which consists of repeating String t, finds t.
System.out.println(
"MamamiaMamamiaMamamia".replaceAll("^(.*)\\1+$", "$1")
); // prints "Mamamia"
The way it works is that the regex captures (.*) into \1, and then sees if there's \1+ following it. Using the ^ and $ ensures...
Maximum number of characters using keystrokes A, Ctrl+A, Ctrl+C and Ctrl+V
This is an interview question from google. I am not able to solve it by myself. Can somebody shed some light?
14 Answers
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ZeroMQ的学习和研究（PHP代码实例） - C/C++ - 清泛网 - 专注C/C++及内核技术
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// Wait for next request from client
$request = $responder->recv ();
printf ("Received request: [%s]\n", $request);
// Do some 'work'
sleep (1);
// Send reply back to client
$responder->send ("World");
}
Client 程序如下：
<?php
/*
* Hello World client
* Connec...
How does database indexing work? [closed]
...in much the same way as linked lists; both contain a section for data, a pointer to the location of the next node (or block), and both need not be stored contiguously.
Due to the fact that a number of records can only be sorted on one field, we can state that searching on a field that isn’t sorte...
How much of a git sha is *generally* considered necessary to uniquely identify a change in a given c
... Note also, though, that this of course only applies for the moment Git prints the SHA. If you "save" abbreviated SHAs (say, in logs, emails, IMs, etc.) and use them later to refer to commits, they might no longer be unique! While certainly unlikely for normal lengths like 7-12 characters, if you d...