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What does .SD stand for in data.table in R
...his is your data.table:
DT = data.table(x=rep(c("a","b","c"),each=2), y=c(1,3), v=1:6)
setkey(DT, y)
DT
# x y v
# 1: a 1 1
# 2: b 1 3
# 3: c 1 5
# 4: a 3 2
# 5: b 3 4
# 6: c 3 6
Doing this may help you see what .SD is:
DT[ , .SD[ , paste(x, v, sep="", collapse="_")], by=y]
# y V1
# 1...
What belongs in an educational tool to demonstrate the unwarranted assumptions people make in C/C++?
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91
The order of evaluation of subexpressions, including
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Find element's index in pandas Series
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++someVariable vs. someVariable++ in JavaScript
...; // This will get array[0]
x = 0;
y = array[++x]; // This will get array[1]
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How can I delete a query string parameter in JavaScript?
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179
"[&;]?" + parameter + "=[^&;]+"
Seems dangerous because it parameter ‘bar’ would...
Capitalize the first letter of both words in a two word string
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12 Answers
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How to format strings in Java
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140
In addition to String.format, also take a look java.text.MessageFormat. The format less terse...
Most efficient way of making an if-elif-elif-else statement when the else is done the most?
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100
The code...
options.get(something, doThisMostOfTheTime)()
...looks like it ought to be fast...