大约有 48,000 项符合查询结果（耗时：0.0454秒） [XML]
Django: Get an object form the DB, or 'None' if nothing matches
...orks exactly as it suppose to. It returns the first object in query result and doesn't cares if multiple results are found. If you need to check for multiple objects returned you should use .get() instead.
– Cesar Canassa
Mar 13 '14 at 15:03
...
Apply a function to every row of a matrix or a data frame
Suppose I have a n by 2 matrix and a function that takes a 2-vector as one of its arguments. I would like to apply the function to each row of the matrix and get a n-vector. How to do this in R?
...
Is 0 a decimal literal or an octal literal?
...
Yes, 0 is an Octal literal in C++.
As per the C++ Standard:
2.14.2 Integer literals [lex.icon]
integer-literal:
decimal-literal integer-suffixopt
octal-literal integer-suffixopt
hexadecimal-literal integer-suffixopt
decimal-literal:
nonzero-digit ...
promise already under evaluation: recursive default argument reference or earlier problems?
...1, f..=f){ g.(1,T, f.=f..) }? In cases with more recursions, is it a good and safe practice adding more .? (2) if f is a non-function argument, for example g <- function(x, T, f=f){ exp(-fx/T) }* and test<- function(g.=g, T=1, f=f){ g.(1,T, f=f.) }, will using the same name for both formal a...
Why does the C preprocessor interpret the word “linux” as the constant “1”?
...
In the Old Days (pre-ANSI), predefining symbols such as unix and vax was a way to allow code to detect at compile time what system it was being compiled for. There was no official language standard back then (beyond the reference material at the back of the first edition of K&R), a...
Cartesian product of multiple arrays in JavaScript
...the newly added flatMap.
Special thanks to ECMAScript 2019 for adding flat and flatMap to the language!
Example
This is the exact example from your question:
let output = cartesian([1,2],[10,20],[100,200,300]);
Output
This is the output of that command:
[ [ 1, 10, 100 ],
[ 1, 10, 200 ],
[ 1, 10...
When to use os.name, sys.platform, or platform.system?
...
Dived a bit into the source code.
The output of sys.platform and os.name are determined at compile time. platform.system() determines the system type at run time.
sys.platform is specified as a compiler define during the build configuration.
os.name checks whether certain os specific...
When to use SELECT … FOR UPDATE?
Please help me understand the use-case behind SELECT ... FOR UPDATE .
2 Answers
2
...
How to sort an array in Bash
...set IFS
Supports whitespace in elements (as long as it's not a newline), and works in Bash 3.x.
e.g.:
$ array=("a c" b f "3 5")
$ IFS=$'\n' sorted=($(sort <<<"${array[*]}")); unset IFS
$ printf "[%s]\n" "${sorted[@]}"
[3 5]
[a c]
[b]
[f]
Note: @sorontar has pointed out that care is re...
JSON left out Infinity and NaN; JSON status in ECMAScript?
Any idea why JSON left out NaN and +/- Infinity? It puts Javascript in the strange situation where objects that would otherwise be serializable, are not, if they contain NaN or +/- infinity values.
...