Compare two arrays and find the index of uncommon elements in SWIFT 3

Question

Arrays are of type String . Since It is time consuming to add "", I have written it like Int. Sorry.

I have two arrays say var array1 = [[1,2,3,4,5,6,7,8,9]] and

var array2 = [[1,2,3,4],
              [2,3,4,5],
              [2,4,5,6],
              [1,2,3,4,5,6,7,8,9],
              [1,2,3,4,5,6,7,8],
              [2,3,4,5,6,7,8]]

I have to compare each array element of array2 with array1 and insert '-' where the elements do not match. Like this,

var array2 = [[1,2,3,4,-,-,-,-,-],
              [-,2,3,4,5,-,-,-,-],
              [-,2,-,4,5,6,-,-,-],
              [1,2,3,4,5,6,7,8,9],
              [1,2,3,4,5,6,7,8,-],
              [-,2,3,4,5,6,7,8,-]]

I tried to iterate over each array in array2 and compare it with array1, compare the indices and insert '-' to at index position i , but I am getting unexpected results.

UPDATE

 for item in array2{
var elementsArray = item
for i  in stride(from: 0, to: elementsArray.count, by: 1) {
    if elementsArray[i] != array1[i]
    {
        elementsArray.insert("-", at: i)
    }
    print("elemnt array.....", elementsArray, "\n\n")
}
}

I had thought of comparing each array of array2 with array1 by count , find the index of uncommon element and then insert '-' at that index position. Is this approach right? Please help me with this.

Answer 1

You want a new array where each row of array2 is replaced by a variant of array1 , with elements not originally present in the row replaced by "-":

let array1 = [1,2,3,4,5,6,7,8,9]
let array2 = [[1,2,3,4],
              [2,3,4,5],
              [2,4,5,6],
              [1,2,3,4,5,6,7,8,9],
              [1,2,3,4,5,6,7,8],
              [2,3,4,5,6,7,8]]

let filled = array2.map { row in 
    array1.map {
        row.contains($0) ? String($0) : "-"
    }
}

for row in filled { print(row) }

Output:

["1", "2", "3", "4", "-", "-", "-", "-", "-"]
["-", "2", "3", "4", "5", "-", "-", "-", "-"]
["-", "2", "-", "4", "5", "6", "-", "-", "-"]
["1", "2", "3", "4", "5", "6", "7", "8", "9"]
["1", "2", "3", "4", "5", "6", "7", "8", "-"]
["-", "2", "3", "4", "5", "6", "7", "8", "-"]

For large arrays this can be improved by creating a Set(row) for a faster containment check, or by utilizing that the elements are in increasing order.

Your approach does not work correctly because elementsArray is modified while iterating over it.