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How to check if object (variable) is defined in R?
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You want exists():
R> exists("somethingUnknown")
[1] FALSE
R> somethingUnknown <- 42
R> exists("somethingUnknown")
[1] TRUE
R>
share
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Why #define TRUE (1==1) in a C boolean macro instead of simply as 1?
...e TRUE and FALSE according to its own rules, you're making their meanings explicit to programmers, and you're guaranteeing consistency within your program and any other library (assuming the other library follows C standards ... you'd be amazed).
Some History
Some BASICs defined FALSE as 0 and TR...
Using group by on multiple columns
I understand the point of GROUP BY x .
2 Answers
2
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Nokogiri installation fails -libxml2 is missing
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First, install the dependencies:
sudo apt-get install libxslt-dev libxml2-dev
If you still receive the error, you may be missing a compiler toolchain:
sudo apt-get install build-essential
You'll get the "libxml2 is missing" error if you're missing a build toolchain (at least I...
How to make the python interpreter correctly handle non-ASCII characters in string operations?
...ions:
The source file must be saved using the correct encoding in your text editor as well.
In Python 2, the unicode literal must have a u before it, as in s.replace(u"Â ", u"") But in Python 3, just use quotes. In Python 2, you can from __future__ import unicode_literals to obtain the Python 3 b...
Best way to give a variable a default value (simulate Perl ||, ||= )
...tly from the conditional operator, as it is specific to a null value. For example, if $_GET['name'] is set to an empty string, the first line would return an empty string, but we could return "john doe" by using $_GET['name'] ? $_GET['name'] : 'john doe'.
– VPhantom
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Executing multi-line statements in the one-line command-line?
I'm using Python with -c to execute a one-liner loop, i.e.:
17 Answers
17
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A route named “x” is already in the route collection. Route names must be unique. Exception with ASP
I'm doing an ASP.NET MVC 3 web service and I keep getting this exception intermittently.
14 Answers
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Is there a way to detect if a browser window is not currently active?
...ilitychange", onchange);
Current browser support:
Chrome 13+
Internet Explorer 10+
Firefox 10+
Opera 12.10+ [read notes]
The following code falls back to the less reliable blur/focus method in incompatible browsers:
(function() {
var hidden = "hidden";
// Standards:
if (hidden in docum...
Iterate a list with indexes in Python
... of for i in range(len(name_of_list)): which is what led me to provide an example using a for instead of what was shown in the first part.
– Vinko Vrsalovic
Sep 27 '12 at 9:29
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