我有一个如下数组:
var array: [Double] = [4, 5, 2, 4, 3, 6]
我想要做的是从这个数组创建一个新数组,其中包含每个值与前一个值相比的百分比差异。所以我上面的数组看起来像:
var newArray = [0, 25, -60, 100, -25, 100]
如果这有道理?非常感谢任何帮助,非常感谢!!
这可以通过zip()
方便地完成,以枚举相邻的数组元素对:
let array: [Double] = [4, 5, 2, 4, 3, 6]
let percentages = [0] + zip(array, array.dropFirst()).map {
(old, new) in
return 100.0 * (new - old) / old
}
print(percentages) // [0.0, 25.0, -60.0, 100.0, -25.0, 100.0]
(假设没有数组元素为零。)
或者使用简写语法:
let percentages = [0] + zip(array, array.dropFirst()).map {
100.0 * ($1 - $0) / $0
}
您可以使用var来保留最后一个元素的引用,并使用defer在map中更新它:
extension Collection where Element: FloatingPoint {
var percentageDifference: [Element] {
guard var last = first else { return [] }
return map { element in
defer { last = element }
return (element - last) / last * 100
}
}
}
let numbers: [Double] = [4, 5, 2, 4, 3, 6]
let percentageDifference = numbers.percentageDifference
print(percentageDifference) // "[0.0, 25.0, -60.0, 100.0, -25.0, 100.0]\n"
你可以这样做:
func percentageDifference(num1: Double, num2: Double) -> Double {
return (num2 - num1) / num1 * 100
}
var array: [Double] = [4, 5, 2, 4, 3, 6]
var resultArray: [Double] = [0]
for i in (1..<array.count) {
resultArray.append(percentageDifference(num1: array[i-1], num2: array[i]))
}
单行:您可以迭代索引并计算结果:
let array: [Double] = [4, 5, 2, 4, 3, 6]
let newArray = array.indices.map { i in (array[i] - array[max(0,i-1)]) / array[max(0, i-1)] * 100.0 }
print(newArray) // [0.0, 25.0, -60.0, 100.0, -25.0, 100.0]
有一个小代码重复,但它以高效的方式工作,我会说:)