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How to sum a variable by group
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Using aggregate:
aggregate(x$Frequency, by=list(Category=x$Category), FUN=sum)
Category x
1 First 30
2 Second 5
3 Third 34
In the example above, multiple dimensions can be specified in the list. Multiple aggregated metrics of the same d...
Find the division remainder of a number
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you are looking for the modulo operator:
a % b
for example:
26 % 7
Of course, maybe they wanted you to implement it yourself, which wouldn't be too difficult either.
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C dynamically growing array
...aw" list of in-game entities, and I intend to make an array holding an index number (int) of an indeterminate number of entities, for processing various things. I would like to avoid using too much memory or CPU for keeping such indexes...
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In c# is there a method to find the max of 3 numbers?
Like Math.Max but takes 3 or params of int?
10 Answers
10
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push_back vs emplace_back
...s strictly equivalent to push_back(Type&& _Val).
But the real C++0x form of emplace_back is really useful: void emplace_back(Args&&...);
Instead of taking a value_type it takes a variadic list of arguments, so that means that you can now perfectly forward the arguments and construc...
Could not load file or assembly Microsoft.SqlServer.management.sdk.sfc version 11.0.0.0
...S SQL Server 2008 R2 and when I try to update model from database under EDMX file I am facing that error.
12 Answers
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Separating class code into a header and cpp file
...d declarations code of a simple class into a new header and cpp file. For example, how would I separate the code for the following class?
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After Installing Java JDK 7 For Mac OS X - mvn -version still shows java version 1.6.0_31
Oracle released Java JDK 7 on April 26 for Mac OS X. I followed the install instructions and when I do java -version in a terminal window I get:
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Why doesn't Dijkstra's algorithm work for negative weight edges?
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Recall that in Dijkstra's algorithm, once a vertex is marked as "closed" (and out of the open set) - the algorithm found the shortest path to it, and will never have to develop this node again - it assumes the path developed to this path is the shortest.
But with negative ...
Differences in boolean operators: & vs && and | vs ||
... the rules for && and || but what are & and | ? Please explain these to me with an example.
11 Answers
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