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.

Is array1 supposed to be a one dimensional array or an array of arrays? In the latter case should the i-th subarray of array1 be compared to the i-th subarray of array2? — Dávid Pásztor
About each array in array2, can it's length be greater than the length of array1? — Adeel
Are the numbers from the second array always present in the first array? Are the numbers always increasing? — Martin R
@Adeel no It cannot be greater. Max length of array present in array2 is equal to array1 — Bella

Martin R Martin R · Accepted Answer · 2017-08-17T13:48:00

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.

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

1 Answers