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Assign multiple columns using := in data.table, by group
...1 hi hello
# 2: 2 2 hi hello
# 3: 3 3 hi hello
# 4: 1 4 hi hello
# 5: 2 5 hi hello
# 6: 3 6 hi hello
x[ , c("mean", "sum") := list(mean(b), sum(b)), by = a][]
# a b col1 col2 mean sum
# 1: 1 1 hi hello 2.5 5
# 2: 2 2 hi hello 3.5 7
# 3: 3 3 hi hello 4.5 9
# 4: 1 4 h...
An “and” operator for an “if” statement in Bash
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265
What you have should work, unless ${STATUS} is empty. It would probably be better to do:
if ! ...
dplyr: “Error in n(): function should not be called directly”
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edited Jan 27 '15 at 0:44
Michael Bellhouse
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How to convert list of key-value tuples into dictionary?
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answered Jul 5 '11 at 17:28
ninjageckoninjagecko
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How do I create an empty array/matrix in NumPy?
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453
You have the wrong mental model for using NumPy efficiently. NumPy arrays are stored in contigu...
Passing route control with optional parameter after root in express?
... Ernesto BadilloErnesto Badillo
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Regular expression to limit number of characters to 10
... options are:
{3} Exactly 3 occurrences;
{6,} At least 6 occurrences;
{2,5} 2 to 5 occurrences.
See the regular expression reference.
Your expression had a + after the closing curly brace, hence the error.
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initialize a vector to zeros C++/C++11
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225
You don't need initialization lists for that:
std::vector<int> vector1(length, 0);
std::v...
“x not in y” or “not x in y”
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answered Jan 5 '12 at 6:45
BenBen
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Boolean literals in PowerShell
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JoeyJoey
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