Andrew Andrew - 4 months ago 13
Swift Question

Pad an array with 0's swift

I am attempting to pad an an array with zeros but cannot find a succinct way to do this in swift.
If I have array x = [1,2,3 ; 4,5,6 ; 7,8,9]
in matlab I could use the command

y = [zeros(1,3+2);zeros(3,1),x,zeros(3,1);zeros(1,3+2)]


giving the desired output array of [0,0,0,0,0; 0,1,2,3,0 ; 0,4,5,6,0 ; 0,7,8,9,0 ; 0,0,0,0,0]

However so far in a swift playground I have only been able to refer to each element individually to correctly form the new array.

The methods I have tried so far using x as the input and y as the output, the first similar to matlab,

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

var y = [[0,0,0,0,0],[0,x[0],0],[0,x[1],0],[0,x[2],0],[0,0,0,0,0]]


The second being a loop

for i in 0 ..< x.count + 1 {
if i == 0 || i == x.count - 1 {
y[i] = [0,0,0,0,0]
}
else{
y[i] = [0, x[i-1] ,0]
}
}


Rather than looking like a standard array in the Xcode playground preview this is the output given.

[[0, 0, 0, 0, 0], [0, […], 0], [0, 0, 0, 0, 0], [0, […], 0], [0, 0, 0, 0, 0]]


which also prints to the console very strangely, using the code

for i in 0 ..< y.count {
print("\(y[i])")
}


the output is

(
0,
0,
0,
0,
0
)
(
0,
(
1,
2,
3
),
0
)
(
0,
0,
0,
0,
0
)
(
0,
(
7,
8,
9
),
0
)
(
0,
0,
0,
0,
0
)


as opposed to the expected

[0, 0, 0, 0, 0]
[0, 1, 2, 3, 0]
[0, 4, 5, 6, 0]
[0, 7, 8, 9, 0]
[0, 0, 0, 0, 0]


What is the best way to do this?

Answer

Extension

If you define this extension

extension _ArrayType where Element == Int {
    func pad(left left: Int, right: Int) -> [Int] {
        let leftSide = [Int](count: left, repeatedValue: 0)
        let rightSide = [Int](count: right, repeatedValue: 0)
        return leftSide + (self as! [Int]) + rightSide
    }
}

you can then write

[1,2,3].pad(left: 1, right: 1) // [0, 1, 2, 3, 0]
Comments