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Assign multiple columns using := in data.table, by group
...b col1 col2
# 1: 1 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 ...
What Are the Differences Between PSR-0 and PSR-4?
... I can't seem to grasp what the actual difference is between PSR-0 and PSR-4.
5 Answers
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What is the difference between Gemfile and Gemfile.lock in Ruby on Rails
... |
edited Mar 29 '18 at 14:02
cori
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answered Aug...
CGRidCtrl控件 学习心得 - C/C++ - 清泛网 - 专注C/C++及内核技术
...能介绍... 1
2.2 框架介绍... 2
2.3 主要类介绍... 4
2.3.1 CGridCtrl类... 4
2.3.2 CGridCellCheck类... 5
2.3.3 CGridCellCombo类... 7
2.4 控件类CGridCtrl常用函数说明... 10
2.4.1 行和列的设置... 10
2.4.2 单元格信息设置.....
Add zero-padding to a string
How do I add "0" padding to a string so that my string length is always 4?
5 Answers
5...
What are the GCC default include directories?
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4 Answers
4
Active
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Why modelVersion of pom.xml is necessary and always set to 4.0.0?
...'s <modelVersion></modelVersion> of pom.xml is always set to 4.0.0.
4 Answers
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What is the optimal Jewish toenail cutting algorithm?
...ort ifilter, permutations
validseqs = ifilter(isValid, permutations([1,2,3,4,5]))
for i in validseqs:
print i
(1, 3, 5, 2, 4)
(1, 4, 2, 5, 3)
(2, 4, 1, 3, 5)
(2, 4, 1, 5, 3)
(2, 5, 3, 1, 4)
(3, 1, 4, 2, 5)
(3, 1, 5, 2, 4)
(3, 5, 1, 4, 2)
(3, 5, 2, 4, 1)
(4, 1, 3, 5, 2)
(4, 2, 5, 1, 3)
(4, 2, 5,...
What is the syntax to insert one list into another list in python?
...
Do you mean append?
>>> x = [1,2,3]
>>> y = [4,5,6]
>>> x.append(y)
>>> x
[1, 2, 3, [4, 5, 6]]
Or merge?
>>> x = [1,2,3]
>>> y = [4,5,6]
>>> x + y
[1, 2, 3, 4, 5, 6]
>>> x.extend(y)
>>> x
[1, 2, 3, 4, 5, ...