slice | 易学教程

Python negative zero slicing

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问题 I often find myself having to work with the last n items in a sequence, where n may be 0. The problem is that trying to slice with [-n:] won't work in the case of n == 0 , so awkward special case code is required. For example if len(b): assert(isAssignableSeq(env, self.stack[-len(b):], b)) newstack = self.stack[:-len(b)] + a else: #special code required if len=0 since slice[-0:] doesn't do what we want newstack = self.stack + a My question is - is there any way to get this behavior without

Rotate Array in Go

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问题 This is a LeetCode problem: 189. Rotate Array: Given an array, rotate the array to the right by k steps, where k is non-negative. Example 1: Input: [1,2,3,4,5,6,7] and k = 3 Output: [5,6,7,1,2,3,4] And here is my solution: func rotate(nums []int, k int) { k = k % len(nums) nums = append(nums[k:],nums[0:k]...) fmt.Println(nums) } It is a straight forward algorithm but it does not work. I am new to Go. I suppose nums is passed by value and changes to nums won't affect the real nums . How can I

Go 基础语法

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转自：http://studygolang.com/topics/548 例子Packages.go： package main import ( "fmt" "math/rand" ) func add(x int, y int) int { return x + y } func main() { fmt.Println("My favorite number is", rand.Intn(10)) fmt.Println(add(42, 13)) } 包：每个 Go 程序都是由包(package)组成的，程序运行的入口是包 main 。导入：这个代码用圆括号组合了导入，这是“打包”导入语句。同样可以编写多个导入语句，例如： import "fmt" import "math" 这个程序使用并导入了包 "fmt" 和" math/rand" 。包名与导入路径的最后一个目录一致。例如，如果你导入了" math/rand" ，那么你就可以在程序里面直接写rand.Intn(10),但如果你导入的是" math" ，那么你就得写math.rand.Intn(10)。函数：函数可以没有参数或接受多个参数。在这个例子中， add 接受两个 int 类型的参数，注意类型在变量名之后。有没有觉得很奇怪呢，下面就详细解释一下go这样做的原因。看一个c的例子： int (*fp)(int

golang删除数组某个元素

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golang中对一个slice进行“slice”可以取片段得到一个新的slice，那么如何用简洁的代码删除slice中的一个元素呢？ a := []int{0, 1, 2, 3, 4} //删除第i个元素 i := 2 a = append(a[:i], a[i+1:]...) 作者：krystollia 链接：https://www.jianshu.com/p/bfde71cac827 来源：简书著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。来源： https://www.cnblogs.com/ExMan/p/12185346.html

Slice NSArray from end of array

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问题 What is the best way to "slice" an NSArray from the end, rather than the beginning, of the array (for example, finding the subarray containing the last few elements of a NSArray of unknown length)? In Python, you can use negative indices to accomplish this, e.g.: new_list = old_list[-5:-3] What's the most natural way to do this in Objective-C? 回答1: There's nothing to match Python's nice syntax for this, but you could do: NSUInteger count = [myArray count]; NSArray * slice = [myArray

jQuery 遍历 - slice() 方法

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今天项目中遇到要获取前几个和最后几个元素，查了资料发现了这个slice()方法很实用，废了一番功夫终于明白怎么用的了。 slice(start[,end]): start 类型： Integer 开始选取子集的位置。第一个元素是0.如果是负数，则可以从集合的尾部开始选起。 end (可选) 类型： Integer 结束选取自己的位置，如果不指定，则就是本身的结尾。如果提供的jQuery代表了一组DOM元素，slice()方法从匹配元素的子集中构造一个新的jQuery对象。所提供的start索引标识的设置一个集合中的元素的位置;如果end被省略，这个元素之后的所有元素将包含在结果中。例如： <ul> <li> list item 1 </li> <li> list item 2 </li> <li> list item 3 </li> <li> list item 4 </li> <li> list item 5 </li> </ul> 1. $( 'li' ).slice( 2 ).css( 'background-color' , 'red' ); 上述代码的执行结果是，第 3，4，5 项列表项的背景色变成了红色。注意，索引是从 0 开始计数的，并且代表的是 jQuery 对象中的元素位置。 2. $( 'li' ).slice( 2 , 4 ).css(

[ jquery 过滤器 slice(start, [end]) ] 此方法用于在选择器的基础之上精确筛选出匹配的子集(可以使用前导限制范围)

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此方法用于在选择器的基础之上精确筛选出匹配的子集(可以使用前导限制范围): 　　1.start: 开始选取子集的位置。第一个元素是0.如果是负数，则可以从集合的尾部开始选起　　2.end: 结束选取自己的位置，如果不指定，则就是本身的结尾　　3.参数包含开始,不包含结束 [ start , end ) 实例: <!DOCTYPE html> <html lang='zh-cn'> <head> <title>Insert you title</title> <meta http-equiv='description' content='this is my page'> <meta http-equiv='keywords' content='keyword1,keyword2,keyword3'> <meta http-equiv='Content-Type' content='text/html; charset=utf-8'> <script type='text/javascript' src='./js/jquery-1.12.1.min.js'></script> <style type='text/css'> </style> <script type='text/javascript'> $(function(){ $('li').each(function

R array manipulation

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问题 In python lists can be sliced like this x[4:-1] to get from the fourth to the last element. In R something similar can be accomplished for vectors with x[4:length(x)] and for multidimensional arrays with something like x[,,,,4:dim(x)[5],,,] . Is this more elegant syntax for array slicing for a particular dimension from an element in the middle to the last element? Thanks 回答1: You could use the drop elements syntax: > (1:10)[-(1:4)] [1] 5 6 7 8 9 10 回答2: In case you are interested in slicing

Garbage collection and correct usage of pointers in Go

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问题 I come from a Python/Ruby/JavaScript background. I understand how pointers work, however, I'm not completely sure how to leverage them in the following situation. Let's pretend we have a fictitious web API that searches some image database and returns a JSON describing what's displayed in each image that was found: [ { "url": "https://c8.staticflickr.com/4/3707/11603200203_87810ddb43_o.jpg", "description": "Ocean islands", "tags": [ {"name":"ocean", "rank":1}, {"name":"water", "rank":2}, {

Garbage collection and correct usage of pointers in Go

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