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Confusion between factor levels and factor labels
...seems to be a difference between levels and labels of a factor in R.
Up to now, I always thought that levels were the 'real' name of factor levels, and labels were the names used for output (such as tables and plots). Obviously, this is not the case, as the following example shows:
...
Change color of PNG image via CSS?
...image to grayscale, sepia and lot more (look at the example).
So you can now change the color of a PNG file with filters.
body {
background-color:#03030a;
min-width: 800px;
min-height: 400px
}
img {
width:20%;
float:left;
margin:0;
}
/*Filter styles*/
.sat...
Postgresql - unable to drop database because of some auto connections to DB
...tever was trying to auto-connect should no longer be able to do so.
You'll now be able to drop the DB.
This won't work if you're using superuser connections for normal operations, but if you're doing that you need to fix that problem first.
After you're done dropping the database, if you create the...
Can you Run Xcode in Linux?
...sed the general hardware requirements 1000 fold (NeXT could run in 8-16MB, now you need GB).
Due to the close marriage of GCC and Objective C and NeXT, your best bet at running XCode natively under Linux would be to do a port (if you can get ahold of the source - good luck) utilizing the GNUStep li...
Visual Studio : short cut Key : Duplicate Line
...fter)
Ctrl + D
In Visual Studio 2017 (pre v15.6)
(edit) This feature is now built-in in VS2017: Ctrl + E, V duplicates a line if nothing is selected, or duplicates selection. You can assign it to a different key combination, or find it in the menu:
See this reference for more information.
Pre...
Why does the use of 'new' cause memory leaks?
I learned C# first, and now I'm starting with C++. As I understand, operator new in C++ is not similar to the one in C#.
...
How to select a CRAN mirror in R
...rg"
options(repos=r)
})
which is in ~/.Rprofile.
Edit: As it is now 2018, we can add that for the last few years the URL "https://cloud.r-project.org" has been preferable as it reflects a) https access and b) an "always-near-you" CDN.
...
Time complexity of Euclid's Algorithm
...o follow what happens over two iterations:
a', b' := a % b, b % (a % b)
Now a and b will both decrease, instead of only one, which makes the analysis easier. You can divide it into cases:
Tiny A: 2a <= b
Tiny B: 2b <= a
Small A: 2a > b but a < b
Small B: 2b > a but b < a
Equal...
jQuery - setting the selected value of a select control via its text description
...
Note that jQuery 1.4 has now changed this behavior to select by value if the attribute has been specified, and only select by text if the value attribute is missing. So in this example $('select').val('Two') will select the second option in 1.3.x, bu...
What is JSON and why would I use it?
...ipt object you must first parse it, var x = JSON.parse('{"x":"y"}');, x is now an object but this is not JSON anymore.
See Javascript object Vs JSON
When working with JSON and JavaScript, you may be tempted to use the eval function to evaluate the result returned in the callback, but this is not...