本文介绍了通过抽取或提取Swift中的第n个元素来进行下采样收集的有效方法的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我正尝试通过抽取或提取第n个元素来对长集合进行降采样.
I'm trying to downsample a long collection by decimating or extracting every nth element.
这是我对数组扩展的要求:
Here's what I got for my array extension:
func downsampled(to threshold: Int) -> [T] {
// Validate that threshold falls in valid range
guard !isEmpty, 1...count ~= threshold else { return Array(self) }
let skip = (count / threshold) + 1
var index = 0
var items = [T]()
while index < count {
items.append(self[index])
index += skip
}
return items
}
我希望原始数组中有50-100k个项目,并且可能会将其降采样到屏幕的本机边界宽度(500-1k点).
I'm expecting 50-100k items in the original array and will probably downsample to the native bounds width of the screen (500-1k points).
是否有更简洁或更有效的方法?
Is there a more concise or efficient way of doing this?
推荐答案
extension RangeReplaceableCollection {
func every(from: Index? = nil, through: Index? = nil, nth: Int) -> Self { .init(stride(from: from, through: through, by: nth)) }
}
extension Collection {
func stride(from: Index? = nil, through: Index? = nil, by: Int) -> AnySequence<Element> {
var index = from ?? startIndex
let endIndex = through ?? self.endIndex
return AnySequence(AnyIterator {
guard index < endIndex else { return nil }
defer { index = self.index(index, offsetBy: by, limitedBy: endIndex) ?? endIndex }
return self[index]
})
}
}
游乐场测试
Playground testing
let array = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
for element in array.stride(by: 3) {
print(element)
}
array.stride(by: 3).forEach {
print($0)
}
let nth = array.every(nth: 3) // [1, 4, 7, 10, 13]
let str = "0123456789"
for character in str.stride(by: 2) {
print(character)
}
str.stride(by: 2).forEach {
print($0)
}
let even = str.every(nth: 2) // "02468"
这篇关于通过抽取或提取Swift中的第n个元素来进行下采样收集的有效方法的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!