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Understanding exactly when a data.table is a reference to (vs a copy of) another data.table
...at gets modified by reference.
DT <- data.table(a = c(1, 2), b = c(11, 12))
newDT <- DT
.Internal(inspect(DT))
# @0000000003B7E2A0 19 VECSXP g0c7 [OBJ,NAM(2),ATT] (len=2, tl=100)
# @00000000040C2288 14 REALSXP g0c2 [NAM(2)] (len=2, tl=0) 1,2
# @00000000040C2250 14 REALSXP g0c2 [NAM(2)]...
Unique combination of all elements from two (or more) vectors
...ybe what you are after
> expand.grid(a,b)
Var1 Var2
1 ABC 2012-05-01
2 DEF 2012-05-01
3 GHI 2012-05-01
4 ABC 2012-05-02
5 DEF 2012-05-02
6 GHI 2012-05-02
7 ABC 2012-05-03
8 DEF 2012-05-03
9 GHI 2012-05-03
10 ABC 2012-05-04
11 DEF 2012-05-04
12 GHI 2012-05-04
13 ABC...
Memoization in Haskell?
... f does what you mean for small values of f by calling, for example: fix f 123 = 144
We could memoize this by defining:
f_list :: [Int]
f_list = map (f faster_f) [0..]
faster_f :: Int -> Int
faster_f n = f_list !! n
That performs passably well, and replaces what was going to take O(n^3) time...
How to attach javadoc or sources to jars in libs folder?
...
12 Answers
12
Active
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How to check if hex color is “too black”?
...reen
var b = (rgb >> 0) & 0xff; // extract blue
var luma = 0.2126 * r + 0.7152 * g + 0.0722 * b; // per ITU-R BT.709
if (luma < 40) {
// pick a different colour
}
EDIT
Since May 2014 tinycolor now has a getBrightness() function, albeit using the CCIR601 weighting factors inst...
GridLayout and Row/Column Span Woe
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edited Aug 9 '12 at 23:36
CommonsWare
873k161161 gold badges21342134 silver badges21612161 bronze badges
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How to select last two characters of a string
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12
slice() reference : developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…
– Offirmo
Oct 30 '...
Merge/flatten an array of arrays
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You can use concat to merge arrays:
var arrays = [
["$6"],
["$12"],
["$25"],
["$25"],
["$18"],
["$22"],
["$10"]
];
var merged = [].concat.apply([], arrays);
console.log(merged);
Using the apply method of concat will just take the second parameter as an array, ...
How to debug Apache mod_rewrite
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answered Mar 9 '12 at 11:02
BenBen
4,04633 gold badges1919 silver badges1919 bronze badges
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Moving and vanishing lines of code; trouble with Eclipse's XML Editor
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edited Nov 7 '12 at 4:03
flyingsandwich
7711 silver badge66 bronze badges
answered Oct 18 '1...