slice

Python : Get many list from a list [duplicate]

由 不羁的心 提交于 2019-12-01 08:21:09
问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: How do you split a list into evenly sized chunks in Python? Hi, I would like to split a list in many list of a length of x elements, like: a = (1, 2, 3, 4, 5) and get : b = ( (1,2), (3,4), (5,) ) if the length is set to 2 or : b = ( (1,2,3), (4,5) ) if the length is equal to 3 ... Is there a nice way to write this ? Otherwise I think the best way is to write it using an iterator ... 回答1: The itertools module

Efficiency of flattening and collecting slices

由 北战南征 提交于 2019-12-01 07:36:36
问题 If one uses the standard .flatten().collect::<Box<[T]>>() on an Iterator<Item=&[T]> where T: Copy , does it: perform a single allocation; and use memcpy to copy each item to the destination or does it do something less efficient? 回答1: Box<[T]> does not implement FromIterator<&T> , so I'll assume your actual inner iterator is something that yields owned T s. FromIterator<T> for Box<[T]> forwards to Vec<T> , which uses size_hint() to reserve space for lower + 1 items, and reallocates as it

How to work with duplicate of a slice in Go?

由 妖精的绣舞 提交于 2019-12-01 07:28:23
问题 mapArray is a 2D slice of float32. I make a copy of it so I can work on the copy without modifying mapArray . However, it's not the case. Assigning a value to Origin modifies mapArray . origins := it.Empty2DArray(len(mapArray)) copy(origins, mapArray) origins[5][5] = -1 Doing that makes mapArray[5][5] to be -1 instead of its original value. How can i make a true independent copy of the slice? Thanks. Edit: // Empty2DArray returns a zeroed 2D array. func Empty2DArray(arraySize int) [][]float32

javascript slice()获取数组中的一部分数据

由 牧云@^-^@ 提交于 2019-12-01 07:05:49
javascript slice()从已有的数组中返回选定的元素。start为必选项，是从0开始计算的索引，end为可选项，表示结束元素的位置，也是从0开始的索引。 <!DOCTYPE html> <html> <head> <title>Runde</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <script type="text/javascript"> var arr = new Array(6) arr[0]="黑龙江" arr[1]="吉林" arr[2]="辽宁" arr[3]="内蒙古" arr[4]="河北" arr[5]="山东" document.write("原有的数组元素:"+arr) document.write("<br />") document.write("获取的部分数组元素:"+arr.slice(2,4)) document.write("<br />") document.write("获取部分元素后的数据:"+arr) </script> </head> <body> </body> </html> 　　 来源： https://www.cnblogs.com/rjbc/p/11666265.html

Yielding until all needed values are yielded, is there way to make slice to become lazy

由 可紊 提交于 2019-12-01 06:52:07
问题 Is there way to stop yielding when generator did not finish values and all needed results have been read? I mean that generator is giving values without ever doing StopIteration. For example, this never stops: (REVISED) from random import randint def devtrue(): while True: yield True answers=[False for _ in range(randint(100,100000))] answers[::randint(3,19)]=devtrue() print answers I found this code, but do not yet understand, how to apply it in this case: http://code.activestate.com/recipes

Pandas DataFrame slicing with iteration

由 核能气质少年 提交于 2019-12-01 06:33:43
问题 I would like to perform some action on sliced DataFrame with multiple slice indexes. The pattern is df.iloc[0:24] , df.iloc[24:48], df.iloc[48:72] and so on with step 24 as you get it. How I can iterate it without to set it manually every time. More like df.iloc[x:z] and each iteration x=0, z=24 and next iteration with 24 step, x will be 24 and z=48 and so on. Thanks in advance, Hristo. 回答1: for loop iteration for i in range(0, len(df), 24): slc = df.iloc[i : i + 24] groupby df.groupby(df

Subset check with slices in Go

由 萝らか妹 提交于 2019-12-01 06:07:46
I am looking for a efficient way to check if a slice is a subset of another. I could simply iterate over them to check, but I feel there has to be a better way. E.g. {1, 2, 3} is a subset of {1, 2, 3, 4} {1, 2, 2} is NOT a subset of {1, 2, 3, 4} What is the best way to do this efficiently? Thanks! I think the most common way to solve a subset problem is via a map. package main import "fmt" // subset returns true if the first array is completely // contained in the second array. There must be at least // the same number of duplicate values in second as there // are in first. func subset(first,

What is the use of into_boxed_slice() methods?

由 混江龙づ霸主 提交于 2019-12-01 05:57:35
问题 Looking at the methods available for Vec<T> I stumbled across into_boxed_slice(self) -> Box<[T]> String also has such a method ( into_boxed_str(self) ). The usefulness of having Deref for Vec<T> / String that allows them to be treated like a shared slice ( &[T] ) is obvious, but I don't see any use for an owned slice ( Box<[T]> ) except, perhaps, FFI. The Rust GitHub repo only uses into_boxed_slice() in a handful of cases. Since methods for creating boxed slices are available in std and this

How can I access a deeply nested dictionary using tuples?

由 让人想犯罪 __ 提交于 2019-12-01 05:35:10
I would like to expand on the autovivification example given in a previous answer from nosklo to allow dictionary access by tuple. nosklo's solution looks like this: class AutoVivification(dict): """Implementation of perl's autovivification feature.""" def __getitem__(self, item): try: return dict.__getitem__(self, item) except KeyError: value = self[item] = type(self)() return value Testing: a = AutoVivification() a[1][2][3] = 4 a[1][3][3] = 5 a[1][2]['test'] = 6 print a Output: {1: {2: {'test': 6, 3: 4}, 3: {3: 5}}} I have a case where I want to set a node given some arbitrary tuple of

Unpacking slice of slices

由 可紊 提交于 2019-12-01 04:50:44
问题 I am curious about unpacking a slice of slices and sending them as arguments to a variadic function. Let's say we have a function with variadic parameters: func unpack(args ...interface{}) If we wan't to pass in a slice of interfaces it works, it doesn't matter if we unpack it or not: slice := []interface{}{1,2,3} unpack(slice) // works unpack(slice...) // works It gets tricky if we have a slice of slices. Here the compiler doesn't let us pass in an unpacked version: sliceOfSlices := [][
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