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Count number of rows within each group
... I don't know but this could be useful as well... df %>% group_by(group, variable) %>% mutate(count = n())
– Manoj Kumar
Dec 14 '16 at 17:57
1
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指定组件的大小 · App Inventor 2 中文网
...s height and width. There are four choices:
Automatic: Size is chosen by the system
Fill parent: Size is chosen to fill the space available.
Size specified in pixels
Size in percent of Screen (not available for all components)
Since not all Android devices have the same screen size, it...
Are there any SHA-256 javascript implementations that are generally considered trustworthy?
...s other implementation platforms, this one is at least partially developed by, and to a certain extent sponsored by, Dan Boneh, who is a well-established and trusted name in cryptography, and means that the project has some oversight by someone who actually knows what he's doing. The project is also...
Align elements side by side
...
Apply float:left; to both of your divs should make them stand side by side.
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MySQL: Sort GROUP_CONCAT values
...oup-concat:
SELECT student_name,
GROUP_CONCAT(DISTINCT test_score ORDER BY test_score DESC SEPARATOR ' ')
FROM student
GROUP BY student_name;
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What's so bad about Template Haskell?
It seems that Template Haskell is often viewed by the Haskell community as an unfortunate convenience. It's hard to put into words exactly what I have observed in this regard, but consider these few examples
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MySQL INNER JOIN select only one row from second table
... SELECT user_ID, MAX(date) maxDate
FROM payments
GROUP BY user_ID
) b ON c.user_ID = b.user_ID AND
c.date = b.maxDate
WHERE a.package = 1
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remove objects from array by object property
How do I remove an object from the array by matching object property?
13 Answers
13
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Is returning by rvalue reference more efficient?
...turns, the temporary object will get destructed. You should return Beta_ab by value, like the following
Beta_ab
Beta::toAB() const {
return Beta_ab(1, 1);
}
Now, it's properly moving a temporary Beta_ab object into the return value of the function. If the compiler can, it will avoid the mo...
What is the difference between :focus and :active?
...:active represents the state when the element is currently being activated by the user.
For example let's say we have a <button>. The <button> will not have any state to begin with. It just exists. If we use Tab to give "focus" to the <button>, it now enters its :focus state. If ...