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Understanding exactly when a data.table is a reference to (vs a copy of) another data.table
...just changing the elements that need to be changed. That's important to avoid for large data, and why := and set() were introduced to data.table.
Now, with our copied newDT we can modify it by reference :
newDT
# a b
# [1,] 1 11
# [2,] 2 200
newDT[2, b := 400]
# a b # See FA...
What MIME type should I use for CSV?
...arameters: None
Optional parameters: name
Encoding considerations: base64 preferred
Security considerations: As with most application types this data is
intended for interpretation by a program that understands the data on
the recipient's system. Recipients need to und...
Git pull results in extraneous “Merge branch” messages in commit log
... to use rebasing instead of merging is possible, but usually you should avoid it. Rebasing allows you to keep a linear history, but also removes any information about the branching that originally happened. It will also cause the history of the current branch being rewritten, recreating all commits ...
What does “abstract over” mean?
...this really means we're integrating by the similarities.
For example, consider a program that takes the sum of the numbers 1, 2, and 3:
val sumOfOneTwoThree = 1 + 2 + 3
This program is not very interesting, since it's not very abstract. We can abstract over the numbers we're summing, by integrat...
What is the fastest integer division supporting division by zero no matter what the result is?
...
Inspired by some of the comments I got rid of the branch on my Pentium and gcc compiler using
int f (int x, int y)
{
y += y == 0;
return x/y;
}
The compiler basically recognizes that it can use a condition flag of the test in the addition.
As pe...
How do you validate a URL with a regular expression in Python?
...
An easy way to parse (and validate) URL's is the urlparse (py2, py3) module.
A regex is too much work.
There's no "validate" method because almost anything is a valid URL. There are some punctuation rules for splitting it up. Absent any punctuati...
Why does pthread_cond_wait have spurious wakeups?
...
The following explanation is given by David R. Butenhof in "Programming with POSIX Threads" (p. 80):
Spurious wakeups may sound strange, but on some multiprocessor systems, making condition wakeup completely predictable might substantially slow all condition var...
Inheriting class methods from modules / mixins in Ruby
...
A common idiom is to use included hook and inject class methods from there.
module Foo
def self.included base
base.send :include, InstanceMethods
base.extend ClassMethods
end
module InstanceMethods
def bar1
'...
Call Go functions from C
...nt {
return a + b
}
// This is the public function, callable from outside this package.
// It forwards the parameters to C.doAdd(), which in turn forwards
// them back to goCallbackHandler(). This one performs the addition
// and yields the result.
func MyAdd(a, b int) int {
return int( C.do...
What does “fragment” mean in ANTLR?
...ll never be counted as a token, it only serves to simplify a grammar.
Consider:
NUMBER: DIGITS | OCTAL_DIGITS | HEX_DIGITS;
fragment DIGITS: '1'..'9' '0'..'9'*;
fragment OCTAL_DIGITS: '0' '0'..'7'+;
fragment HEX_DIGITS: '0x' ('0'..'9' | 'a'..'f' | 'A'..'F')+;
In this example, matching a NUMBER w...