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What is the best regular expression to check if a string is a valid URL?

...re in PCRE syntax. For absolute IRIs (internationalized): /^[a-z](?:[-a-z0-9\+\.])*:(?:\/\/(?:(?:%[0-9a-f][0-9a-f]|[-a-z0-9\._~\x{A0}-\x{D7FF}\x{F900}-\x{FDCF}\x{FDF0}-\x{FFEF}\x{10000}-\x{1FFFD}\x{20000}-\x{2FFFD}\x{30000}-\x{3FFFD}\x{40000}-\x{4FFFD}\x{50000}-\x{5FFFD}\x{60000}-\x{6FFFD}\x{70000...
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Regular expression that matches valid IPv6 addresses

... 30 Answers 30 Active ...
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Understanding the Use of ColorMatrix and ColorMatrixColorFilter to Modify a Drawable's Hue

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xkcd style graphs in MATLAB

...nshot, and IMTRANSFORM to get a transformation. %# define plot data x = 1:0.1:10; y1 = sin(x).*exp(-x/3) + 3; y2 = 3*exp(-(x-7).^2/2) + 1; %# plot fh = figure('color','w'); hold on plot(x,y1,'b','lineWidth',3); plot(x,y2,'w','lineWidth',7); plot(x,y2,'r','lineWidth',3); xlim([0.95 10]) ylim([0 5]...
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Validating IPv4 addresses with regexp

...tion, but without much luck. It seemed at one point I had had it with (25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?(\.|$)){4} , but it produces some strange results: ...
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What is the easiest way to remove the first character from a string?

... I kind of favor using something like: asdf = "[12,23,987,43" asdf[0] = '' p asdf # >> "12,23,987,43" I'm always looking for the fastest and most readable way of doing things: require 'benchmark' N = 1_000_000 puts RUBY_VERSION STR = "[12,23,987,43" Benchmark.bm(7) do |b| ...
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Convert light frequency to RGB?

... answered Sep 24 '09 at 15:47 Stephen MesaStephen Mesa 4,31333 gold badges2121 silver badges1616 bronze badges ...
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How to find list intersection?

... answered Sep 13 '10 at 1:32 Mark ByersMark Byers 683k155155 gold badges14681468 silver badges13881388 bronze badges ...
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Context switches much slower in new linux kernels

We are looking to upgrade the OS on our servers from Ubuntu 10.04 LTS to Ubuntu 12.04 LTS. Unfortunately, it seems that the latency to run a thread that has become runnable has significantly increased from the 2.6 kernel to the 3.2 kernel. In fact the latency numbers we are getting are hard to belie...
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How to change the order of DataFrame columns?

...ged as needed. This is what you have now: In [6]: df Out[6]: 0 1 2 3 4 mean 0 0.445598 0.173835 0.343415 0.682252 0.582616 0.445543 1 0.881592 0.696942 0.702232 0.696724 0.373551 0.670208 2 0.662527 0.955193 0.131016 0.609548 0.8046...