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Convert a float64 to an int in Go
...
213
package main
import "fmt"
func main() {
var x float64 = 5.7
var y int = int(x)
fmt.Print...
Haskell: Where vs. Let
...parameters of the function f (there are none) and things in outer scopes.
2: To use a where in the first example, you can introduce a second named function
that takes the x as a parameter, like this:
f = State f'
f' x = y
where y = ... x ...
or like this:
f = State f'
where
f' x = y...
Should I use a data.frame or a matrix?
...e the choice.
Also:
Matrices are more memory efficient:
m = matrix(1:4, 2, 2)
d = as.data.frame(m)
object.size(m)
# 216 bytes
object.size(d)
# 792 bytes
Matrices are a necessity if you plan to do any linear algebra-type of operations.
Data frames are more convenient if you frequently refer to ...
Reduce, fold or scan (Left/Right)?
...
372
In general, all 6 fold functions apply a binary operator to each element of a collection. The re...
`elif` in list comprehension conditionals
...
259
Python's conditional expressions were designed exactly for this sort of use-case:
>>>...
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...
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...
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...
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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Java SE 6 vs. JRE 1.6 vs. JDK 1.6 - What do these mean?
...uild 1.6.0_07-b06"), and the HotSpot version (on mine, that's "build 10.0-b23, mixed mode"). I suspect the "11.0" you are seeing is the HotSpot version.
Update: HotSpot is (or used to be, now they seem to use it to mean the whole VM) the just-in-time compiler that is built in to the Java Virtual M...