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What's the fastest way to merge/join data.frames in R?
...he first. If there are duplicates in the second data frame then the match and merge approaches are not the same. Match is, of course, faster since it is not doing as much. In particular it never looks for duplicate keys. (continued after code)
DF1 = data.frame(a = c(1, 1, 2, 2), b = 1:4)
DF2 = da...
Detecting when a div's height changes using jQuery
I've got a div that contains some content that's being added and removed dynamically, so its height is changing often. I also have a div that is absolutely positioned directly underneath with javascript, so unless I can detect when the height of the div changes, I can't reposition the div below it.
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What is the argument for printf that formats a long?
...
On most platforms, long and int are the same size (32 bits). Still, it does have its own format specifier:
long n;
unsigned long un;
printf("%ld", n); // signed
printf("%lu", un); // unsigned
For 64 bits, you'd want a long long:
long long n;
uns...
Algorithms based on number base systems? [closed]
...erical Representations": essentially, take some representation of a number and convert it into a data structure. To give a flavor, here are the sections of that chapter:
Positional Number Systems
Binary Numbers (Binary Random-Access Lists, Zeroless Representations, Lazy Representations, Segmented ...
Remove multiple whitespaces
I'm getting $row['message'] from a MySQL database and I need to remove all whitespace like \n \t and so on.
15 Answer...
Where is the itoa function in Linux?
itoa() is a really handy function to convert a number to a string. Linux does not seem to have itoa() , is there an equivalent function or do I have to use sprintf(str, "%d", num) ?
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Is there a “do … while” loop in Ruby?
...ere Matz states:
|> Don't use it please. I'm regretting this feature, and I'd like to
|> remove it in the future if it's possible.
|
|I'm surprised. What do you regret about it?
Because it's hard for users to tell
begin <code> end while <cond>
works differently from
<...
Why does Dijkstra's algorithm use decrease-key?
...ueue small, thus keeping the total number of priority queue dequeues small and the cost of each priority queue balance low.
In an implementation of Dijkstra's algorithm that reinserts nodes into the priority queue with their new priorities, one node is added to the priority queue for each of the m ...
How do you set, clear, and toggle a single bit?
How do you set, clear, and toggle a bit?
30 Answers
30
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How do I get bit-by-bit data from an integer value in C?
...( 1 << k )) >> k
Here we create a mask, apply the mask to n, and then right shift the masked value to get just the bit we want. We could write it out more fully as:
int mask = 1 << k;
int masked_n = n & mask;
int thebit = masked_n >> k;
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