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Difference between dispatch_async and dispatch_sync on serial queue?
....
for this code
dispatch_async(_serialQueue, ^{ printf("1"); });
printf("2");
dispatch_async(_serialQueue, ^{ printf("3"); });
printf("4");
It may print 2413 or 2143 or 1234 but 1 always before 3
for this code
dispatch_sync(_serialQueue, ^{ printf("1"); });
printf("2");
dispatch_sync(_serialQu...
How can you sort an array without mutating the original array?
...);
the spread-syntax as array literal (copied from mdn):
var arr = [1, 2, 3];
var arr2 = [...arr]; // like arr.slice()
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator
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Apache: “AuthType not set!” 500 Error
... the line that says
Require all granted
it's only needed on Apache >=2.4
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Unique combination of all elements from two (or more) vectors
...
this maybe what you are after
> expand.grid(a,b)
Var1 Var2
1 ABC 2012-05-01
2 DEF 2012-05-01
3 GHI 2012-05-01
4 ABC 2012-05-02
5 DEF 2012-05-02
6 GHI 2012-05-02
7 ABC 2012-05-03
8 DEF 2012-05-03
9 GHI 2012-05-03
10 ABC 2012-05-04
11 DEF 2012-05-04
12 GHI 2012-0...
二维码的生成细节及原理 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...一下二维码一共有40个尺寸。官方叫版本Version。Version 1是21 x 21的矩阵，Version 2是 25 x 25的矩阵，Version 3是29的尺寸，每增加一个version，就会增加4的尺寸，公式是：(V-1)*4 + 21（V是版本号） 最高Version 40，(40-1)*4+21 = 177，所以最高是...
pass **kwargs argument to another function with **kwargs
...3 arguments: filename, mode and a dictionary (kwargs). But Python expects: 2 formal arguments plus keyword arguments.
By prefixing the dictionary by '**' you unpack the dictionary kwargs to keywords arguments.
A dictionary (type dict) is a single variable containing key-value pairs.
"Keyword argu...
Select multiple columns in data.table by their numeric indices
...llowing all just work:
library(data.table)
dt <- data.table(a = 1, b = 2, c = 3)
# select single column by index
dt[, 2]
# b
# 1: 2
# select multiple columns by index
dt[, 2:3]
# b c
# 1: 2 3
# select single column by name
dt[, "a"]
# a
# 1: 1
# select multiple columns by name
dt[, ...
Iterate a list with indexes in Python
... 19] and makes it into iterable list of tuples, like so: [(0,3), (1,7), (2,19)] to use it instead of:
6 Answers
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Select first 4 rows of a data.frame in R
...et the rows 5 to 7?
– Bustergun
May 21 '18 at 9:38
You can use the "index" answer pointed out elsewhere. In this situa...
Selecting pandas column by location
... to mind:
>>> df
A B C D
0 0.424634 1.716633 0.282734 2.086944
1 -1.325816 2.056277 2.583704 -0.776403
2 1.457809 -0.407279 -1.560583 -1.316246
3 -0.757134 -1.321025 1.325853 -2.513373
4 1.366180 -1.265185 -2.184617 0.881514
>>> df.iloc[...