## Creating an array based on the percentage difference of each values of a previous element

I have an array that is the following:

var array: [Double] = [4, 5, 2, 4, 3, 6]

What I would like to do is create a new array from this array that contains the percentage difference of each value compared to its previous one. So my above array would look like:

var newArray = [0, 25, -60, 100, -25, 100]

If that makes sense? Any help is greatly appreciated, many thanks!!

This can be conveniently done with `zip()`

to enumerate over pairs
of adjacent array elements:

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]

(It is assumed that none of the array elements is zero.)

Or with shorthand syntax:

let percentages = [0] + zip(array, array.dropFirst()).map { 100.0 * ($1 - $0) / $0 }

**How do you calculate percentage change between sequential ,** Creating an array based on the percentage difference of each values of a previous element. python list difference between consecutive elements numpy setdiff Often, the elements of an array represent a series of values to be used in a calculation. For example, if the elements of an array represent exam grades, a professor may wish to total the elements of the array and use that sum to calculate the class average for the exam. The program sums the values contained in the 10-element integer array a

You can use a var to keep a reference of the last element and use defer to update it inside map:

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"

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You can do it this way:

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])) }

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One-liner: you could iterate over the indices and compute the result:

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]

Has a minor code duplication, however it does it job in a performant manner, I'd say :)

**Python,** An array of percentage change values for the five categories is used to The projected sales for 2010 are based on the actual sales for 2009. Define array DEPT to hold the sales results for the five categories. Define temporary array GROWTH. Initialize the five elements of GROWTH with the annual projected percentage In Excel, an Array Formula allows you to do powerful calculations on one or more value sets. The result may fit in a single cell or it may be an array. An array is just a list or range of values, but an Array Formula is a special type of formula that must be entered by pressing Ctrl + Shift + Enter.

**Python,** Python | Calculate difference between adjacent elements in given list. Given a list, the task is to create a new list containing difference of adjacent elements in the given list. ini_list = np.array([ 5 , 4 , 89 , 12 , 32 , 45 ]) List with common elements in a List of Lists · Python | Add list elements with a multi-list based on index NumPy arange() is one of the array creation routines based on numerical ranges. It creates an instance of ndarray with evenly spaced values and returns the reference to it. You can define the interval of the values contained in an array, space between them, and their type with four parameters of arange():

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