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What is the purpose of setting a key in data.table?
... for earlier (outdated) answers.
What exactly does setkey(DT, a, b) do?
It does two things:
reorders the rows of the data.table DT by the column(s) provided (a, b) by reference, always in increasing order.
marks those columns as key columns by setting an attribute called sorted to DT.
The re...
Recursive Lock (Mutex) vs Non-Recursive Lock (Mutex)
...he same thread can lock the same mutex twice and won't deadlock. Of course it also needs to unlock it twice, otherwise no other thread can obtain the mutex. Not all systems supporting pthreads also support recursive mutexes, but if they want to be POSIX conform, they have to .
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Make an image width 100% of parent div, but not bigger than its own width
I’m trying to get an image (dynamically placed, with no restrictions on dimensions) to be as wide as its parent div, but only as long as that width isn’t wider than its own width at 100%. I’ve tried this, to no avail:
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Difference between Big-O and Little-O Notation
What is the difference between Big-O notation O(n) and Little-O notation o(n) ?
4 Answers
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Why aren't programs written in Assembly more often? [closed]
It seems to be a mainstream opinion that assembly programming takes longer and is more difficult to program in than a higher level language such as C. Therefore it seems to be recommend or assumed that it is better to write in a higher level language for these reasons and for the reason of better po...
Hidden features of Windows batch files
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edited Aug 7 '10 at 18:00
community wiki
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How to replace case-insensitive literal substrings in Java
...CharSequence replacement) in String, how can I make the target case-insensitive?
8 Answers
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Targeting position:sticky elements that are currently in a 'stuck' state
position: sticky works on some mobile browsers now, so you can make a menu bar scroll with the page but then stick to the top of the viewport whenever the user scrolls past it.
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How to format a Java string with leading zero?
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In case you have to do it without the help of a library:
("00000000" + "Apple").substring("Apple".length())
(Works, as long as your String isn't longer than 8 chars.)
sh...
What is the difference between char * const and const char *?
...* const
which is a constant pointer to a constant char (so nothing about it can be changed).
Note:
The following two forms are equivalent:
const char *
and
char const *
The exact reason for this is described in the C++ standard, but it's important to note and avoid the confusion. I know se...