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How do I combine two data-frames based on two columns? [duplicate]
I know I can use the plyr and its friends to combine dataframes, and merge as well, but so far I don't know how to merge two dataframes with multiple columns based on 2 columns?
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How can we access context of an application in Robolectric?
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Update.
Just use for version 1.x and 2.x:
Robolectric.application;
And for version 3.x:
RuntimeEnvironment.application;
And for version 4.x:
add to your build.gradle file:
testImplementation 'androidx.test:core:1.0.0'
retrieve the context with:
Ap...
What is the .idea folder?
...each newly
created project.
Check this documentation for the IDE settings and here is their recommendation on Source Control and an example .gitignore file.
Note: If you are using git or some version control system, you might want to set this folder "ignore".
Example - for git, add this directory t...
How to center an element horizontally and vertically
...le
In supported browsers, set the display of the targeted element to flex and use align-items: center for vertical centering and justify-content: center for horizontal centering. Just don't forget to add vendor prefixes for additional browser support (see example).
html, body, .container {
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Get the current git hash in a Python script
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The git describe command is a good way of creating a human-presentable "version number" of the code. From the examples in the documentation:
With something like git.git current tree, I get:
[torvalds@g5 git]$ git describe parent
v1.0.4-14-g24147...
What is the difference between ? and Object in Java generics?
...Eclipse seems to be giving me an option to choose between a type of Object and a type of '?'.
6 Answers
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Clone contents of a GitHub repository (without the folder itself)
...en I git clone (git@github:me/name.git...) I get a folder called name/ and inside name I have my contents... How do I get JUST the contents?
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How to rethrow InnerException without losing stack trace in C#?
...s now the ExceptionDispatchInfo class.
This lets you capture an exception and re-throw it without changing the stack-trace:
try
{
task.Wait();
}
catch(AggregateException ex)
{
ExceptionDispatchInfo.Capture(ex.InnerException).Throw();
}
This works on any exception, not just AggregateExcep...
cannot load such file — bundler/setup (LoadError)
...tion with Ruby 2.0, but I'm getting "Web application could not be started" and get this trace:
18 Answers
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Algorithm to get the excel-like column name of a number
I'm working on a script that generate some Excel documents and I need to convert a number into its column name equivalent. For example:
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