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Pass a data.frame column name to a function
...l_name,col1,col2){
df$col_name <- df$col1 + df$col2
df
}
#Call foo() like this:
foo(dat,z,x,y)
The problem here is that df$col1 doesn't evaluate the expression col1. It simply looks for a column in df literally called col1. This behavior is described in ?Extract under the secti...
What is the use of hashCode in Java?
...
Buckets aside, hashcode is a method that the object calls to determine the order to store each object in memory. If objects are equal, then their hashcode must also be equal. (converse of this statement is false)
– NoName
Jun 24 '17 at 6:1...
What is the difference between const int*, const int * const, and int const *?
...= int const *
const int * const == int const * const
If you want to go really crazy you can do things like this:
int ** - pointer to pointer to int
int ** const - a const pointer to a pointer to an int
int * const * - a pointer to a const pointer to an int
int const ** - a pointer to a pointer t...
Why was “Avoid Enums Where You Only Need Ints” removed from Android's performance tips?
...ume that a developer is only adding enums where they're useful. The only really bad use I've seen of enums was in some harmony code where they really wanted ints (for bitmasks and the like) and the "enum" wasn't an enum in any reasonable sense. If you find yourself calling "ordinal()" a lot, that's ...
Good reasons NOT to use a relational database?
...l system)
Very good support for versioning of data
Berkeley DB (Basically, a disk based hashtable)
Very simple conceptually (just un-typed key/value)
Quite fast
No administration overhead
Supports transactions I believe
Amazon's Simple DB
Much like Berkeley DB I believe, but hosted
...
What is the difference between named and positional parameters in Dart?
...ss the similarities.
Dart's optional parameters are optional in that the caller isn't required to specify a value for the parameter when calling the function.
Optional parameters can only be declared after any required parameters.
Optional parameters can have a default value, which is used when a...
Why are empty catch blocks a bad idea? [closed]
...-catch , which people (including Jon Skeet) say empty catch blocks are a really bad idea? Why this? Is there no situation where an empty catch is not a wrong design decision?
...
What is the difference between a framework and a library?
...
Actually these terms can mean a lot of different things depending the context they are used.
For example, on Mac OS X frameworks are just libraries, packed into a bundle. Within the bundle you will find an actual dynamic librar...
Why is MATLAB so fast in matrix multiplication?
...
Here's my results using MATLAB R2011a + Parallel Computing Toolbox on a machine with a Tesla C2070:
>> A = rand(1024); gA = gpuArray(A);
% warm up by executing the operations a couple of times, and then:
>> tic, C = A * A; toc
Elapsed time is 0.075396 sec...
How many classes should I put in one file? [closed]
...
A Python file is called a "module" and it's one way to organize your software so that it makes "sense". Another is a directory, called a "package".
A module is a distinct thing that may have one or two dozen closely-related classes. The tri...