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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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Rename a class in Xcode: Refactor… is grayed out (disabled). Why?
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Very sad, almost 2 years later and it still won't refactor the Objective-C objects.
– christophercotton
Apr 10 '11 at 22:42
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Create a .txt file if doesn't exist, and if it does append a new line
I would like to create a .txt file and write to it, and if the file already exists I just want to append some more lines:
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How can I get column names from a table in SQL Server?
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You can obtain this information and much, much more by querying the Information Schema views.
This sample query:
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = N'Customers'
Can be made over all these DB objects:
CHECK_CONSTRAINTS
COL...
Eclipse fonts and background color
...e been trying to change the background color of Eclipse's windows to black and customize the font colors. There doesn't seem to be a way to do this, at least not in an obvious way. I am using version 3.3.
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Centering a view in its superview using Visual Format Language
I just started learning AutoLayout for iOS and had a look at Visual Format Language.
14 Answers
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Python: How do I make a subclass from a superclass?
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The only reason to avoid super is if you don't understand the differences between how super works in Python, and how super/parent works in other languages. Admittedly this is not obvious to people coming from other languages, but I wouldn't conclude that that qualifies it as som...
How do I link to Google Maps with a particular longitude and latitude?
I have a small application that gives the current location: longitude and latitude.
Now I have to browse to google maps with the longitude and latitude.
Please suggest how I can do this.
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How to resize the iPhone/iPad Simulator?
...ke one third the size of the real iPad screen) on my 23" Full-HD screen (and also on the 15" MacBook Pro ).
11 Answers
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Spring Boot JPA - configuring auto reconnect
...little Spring Boot JPA web application. It is deployed on Amazon Beanstalk and uses an Amazon RDS for persisting data. It is however not used that often and therefore fails after a while with this kind of exception:
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