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How can I count the number of matches for a regex?
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177
matcher.find() does not find all matches, only the next match.
Solution for Java 9+
long mat...
When should I use Struct vs. OpenStruct?
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180
With an OpenStruct, you can arbitrarily create attributes. A Struct, on the other hand, must ...
What is this operator in MySQL?
...perator, two values are compared and the result is either 0 (not equal) or 1 (equal); in other words: 'a' <=> 'b' yields 0 and 'a' <=> 'a' yields 1.
Unlike the regular = operator, values of NULL don't have a special meaning and so it never yields NULL as a possible outcome; so: 'a' <=...
How to match a String against string literals in Rust?
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101
You can do something like this:
match &stringthing[..] {
"a" => println!("0"),
...
How do I create test and train samples from one dataframe with pandas?
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I would just use numpy's randn:
In [11]: df = pd.DataFrame(np.random.randn(100, 2))
In [12]: msk = np.random.rand(len(df)) < 0.8
In [13]: train = df[msk]
In [14]: test = df[~msk]
And just to see this has worked:
In [15]: len(test)
Out[15]: 21
In [16]:...
What does the caret operator (^) in Python do?
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177
It's a bitwise XOR (exclusive OR).
It results to true if one (and only one) of the operands (...
How to add leading zeros?
...of digits to begin with, so let's try a harder example of making powers of 10 width 8 too.
anim <- 25499:25504
x <- 10 ^ (0:5)
paste (and it's variant paste0) are often the first string manipulation functions that you come across. They aren't really designed for manipulating numbers, but...
What is q=0.5 in Accept* HTTP headers?
...tor. It specifies what language the user would prefer, on a scale of 0 to 1, as can be seen from the HTTP/1.1 Specification, §14.4:
Each language-range MAY be given an associated quality value which represents an estimate of the user's preference for the languages specified by that range. The qua...
Code Golf: Collatz Conjecture
Inspired by http://xkcd.com/710/ here is a code golf for it.
70 Answers
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