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Summarizing multiple columns with dplyr? [duplicate]
... a bit with the dplyr-syntax. I have a data frame with different variables and one grouping variable. Now I want to calculate the mean for each column within each group, using dplyr in R.
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C++ static virtual members?
Is it possible in C++ to have a member function that is both static and virtual ? Apparently, there isn't a straightforward way to do it ( static virtual member(); is a compile error), but is there at least a way to achieve the same effect?
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Comparing two collections for equality irrespective of the order of items in them
...g answers, since it takes nulls into account, implements IEqualityComparer and has some efficiency and edge case checks. plus, it's Microsoft :)
public class MultiSetComparer<T> : IEqualityComparer<IEnumerable<T>>
{
private readonly IEqualityComparer<T> m_comparer;
p...
Writing a compiler in its own language
...nguage Foo. You use the first bootstrap compiler to compile the compiler, and then use this compiled compiler to compile everything else (including future versions of itself).
Most languages are indeed created in this fashion, partially because language designers like to use the language they are ...
How to match, but not capture, part of a regex?
...regular expression matches only apple or banana if it’s preceded by 123- and followed by -456, or it matches the empty string if it’s preceded by 123- and followed by 456.
|Lookaround | Name | What it Does |
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How does internationalization work in JavaScript?
...environment’s current locale. This function is implementation-dependent, and
it is permissible, but not encouraged, for it to return the same thing as toString.
Every localization method defined in the spec is defined as "implementation-dependent", which results in a lot of inconsistencies. In t...
What are the differences between B trees and B+ trees?
In a b-tree you can store both keys and data in the internal and leaf nodes , but in a b+ tree you have to store the data in the leaf nodes only .
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php execute a background process
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Assuming this is running on a Linux machine, I've always handled it like this:
exec(sprintf("%s > %s 2>&1 & echo $! >> %s", $cmd, $outputfile, $pidfile));
This launches the command $cmd, redirects the command output to $outputfile, and writes the process id to...
How do I create a self-signed certificate for code signing on Windows?
...2, Windows Server 2012 R2, or Windows 8.1 then MakeCert is now deprecated, and Microsoft recommends using the PowerShell Cmdlet New-SelfSignedCertificate.
If you're using an older version such as Windows 7, you'll need to stick with MakeCert or another solution. Some people suggest the Public Key I...
How to use arguments from previous command?
I know that Esc + . gives you the last argument of the last command.
11 Answers
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