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Formula to determine brightness of RGB color
I'm looking for some kind of formula or algorithm to determine the brightness of a color given the RGB values. I know it can't be as simple as adding the RGB values together and having higher sums be brighter, but I'm kind of at a loss as to where to start.
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How to check if PHP array is associative or sequential?
PHP treats all arrays as associative, so there aren't any built in functions. Can anyone recommend a fairly efficient way to check if an array contains only numeric keys?
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How to swap keys and values in a hash
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Ruby has a helper method for Hash that lets you treat a Hash as if it was inverted (in essence, by letting you access keys through values):
{a: 1, b: 2, c: 3}.key(1)
=> :a
If you want to keep the inverted hash, then Hash#...
Java String - See if a string contains only numbers and not letters
...ave a string that I load throughout my application, and it changes from numbers to letters and such. I have a simple if statement to see if it contains letters or numbers but, something isn't quite working correctly. Here is a snippet.
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Split (explode) pandas dataframe string entry to separate rows
...ld and create a new row per entry (assume that CSV are clean and need only be split on ','). For example, a should become b :
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Is there XNOR (Logical biconditional) operator in C#?
I'm new to C# and could not find XNOR operator to provide this truth table:
4 Answers
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Compare two data.frames to find the rows in data.frame 1 that are not present in data.frame 2
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This doesn't answer your question directly, but it will give you the elements that are in common. This can be done with Paul Murrell's package compare:
library(compare)
a1 <- data.frame(a = 1:5, b = letters[1:5])
a2 <- data.frame(a = 1:3, b = letters[1:3])
compa...
Regex lookahead, lookbehind and atomic groups
I found these things in my regex body but I haven't got a clue what I can use them for.
Does somebody have examples so I can try to understand how they work?
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numpy matrix vector multiplication [duplicate]
...ollowing normal matrix multiplication rules, a (n x 1) vector is expected, but I simply cannot find any information about how this is done in Python's Numpy module.
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App Inventor 2 数学代码块 · App Inventor 2 中文网
... 最小值 (min)
最大值 (max)
平方根 (square root)
绝对值 (abs)
相反数 (neg)
对数 (log)
e^
四舍五入 (round)
上取整 (ceiling)
下取整 (floor)
求模 (modulo)
余数 (remainder)
商 (quotient)
正弦 (sin)
余弦 (cos)
正切 (tan)
反正弦 (asin...