Btukfyl

How can I compare the two consecutive numbers in an array and find its count.

let numberArray = [1,2,4,6,7,10,12,13]

// I want to compare two consecutive numbers like [1,2], [4,6], [7,10], [12,13]

For example:

First, I want to calculate difference of the first two numbers[1,2(difference=1)]in the array, then the next two numbers[4,6(difference=2)], then[7,10(difference=3)] and [12,13(difference=1)] at last.

Lastly, I want to count a number of difference that has 1. In this case the count is 2.

What method should I use for this one?

Thanks in advance.

From this answer by Martin R, you can check how to create pairs as below,

let input = [1,2,4,6,7,10,12,13]

let output = stride(from: 0, to: input.count - 1, by: 2).map{(input[$0], input[$0 + 1])}

Now you can create differences array and find the one's count as below,

let differences = output.map({ $0.1 - $0.0 })

let onesCount = differences.filter({ $0 == 1}).count



print(differences)

print(onesCount)

Output

[1, 2, 3, 1]

2

I'm sure there are nicer ways to do this (but it's Monday morning).
One easy solution is to loop through the array using a stride, allowing you to take steps off two.
You then append each difference to a new difference array.
And finally use a filter on this resulting array to determine how often that difference occurs.

let difference      = 1

let array           = [1,2,4,6,7,10,12,13]

var differenceArray = [Int]()

for index in stride(from: 1, to: array.count, by: 2) {

    let difference  = array[index]-array[index-1]

    differenceArray.append(difference)

}



print(differenceArray.filter{ $0 == difference }.count)

Good answer by @Philip. Here is an updated solution also handled other cases.

let numbers = [1, 2, 5, 4, 10, 6, 7, 8, 11, 10, 23]

var allDifference: [Int] = 

for index in stride(from: 0, to: numbers.count, by: 2) {

   let firstValue = numbers[index]

   let secondValue = ((index == numbers.count - 1 && numbers.count % 2 != 0) ? 0 : numbers[index + 1])

   allDifference.append(abs(firstValue - secondValue))

}



let oneDifferenceCount = allDifference.filter { $0 == 1 }.count

print("Result: ", oneDifferenceCount)

You can achieve this with a 2 lines of code using zip compactMap and reduce:

First we create a tuple of consecutive elements, we use zip in order to use the index of the element and compactMap to filter nil elements then we reduce the new array to count only the tuples with a difference of 1

//Create tuples of consecutive values

let tuples = zip(numberArray.indices, numberArray).compactMap{$0 % 2 == 0 ? nil : (numberArray[$0-1],$1) }

// reduce to count only the tuples with difference of 1

let diffOneCount = tuples.reduce(0,{$1.0+1 == $1.1 ? $0+1 : $0})