Copy value of the previous array for preceding 0 in swift 4 - swift3

Question

In swift I have an array like this:
var array = [ 70, 75, 0, 0, 0, 87, 90, 85, 0]
What I want to do is when the value is 0 it will copy the previous first value which is not equal to 0. So the output will become:
[ 70, 75,75, 75, 75, 87, 90, 85, 85]
I’ve tried this code below:
func fillingEmpValues(dataArray:[Int]) -> [Int?] {
var newValue = [Int]()
var array = dataArray
for (index, var element) in array.reversed().enumerated() {
if (element == 0) { // if element is 0
if(index != 0) { // if the index is not 0 proceed
array[index] = (dataArray.reversed()[index-1])
}
}
}
return newValue
}
But the codes above is not working as I expected the output is still the same. What am i MISSING? Thanks

Answer 1

Your code does not work because nothing is appended to newValue. Please notice the yellow warnings.
My suggestion uses a temporary variable (temp).
In the loop
if the value != 0 the value is appended and the temporary variable is set to the value.
if the value == 0 the temporary variable is appended.
func fillingEmpValues(dataArray:[Int]) -> [Int] {
var newValue = [Int]()
var temp = 0
for element in dataArray {
if element != 0 {
newValue.append(element)
temp = element
} else {
newValue.append(temp)
}
}
return newValue
}
let array = [ 70, 75, 0, 0, 0, 87, 90, 85, 0]
let filledArray = fillingEmpValues(dataArray: array) // [70, 75, 75, 75, 75, 87, 90, 85, 85]
Note: Why is your return value [Int?]? Optionals are not involved at all.
Edit:
The other condition in the comments can be accomplished with
func fillingEmpValues(dataArray:[Int]) -> [Int] {
var newValue = [Int]()
var temp = dataArray.first{ $0 != 0 } ?? 0
for (index, element) in dataArray.enumerated() {
if element != 0 {
newValue.append(element)
} else {
temp = dataArray.dropFirst(index).first{ $0 != 0 } ?? temp
newValue.append(temp)
}
}
return newValue
}
let array = [ 0, 0, 83, 0, 0, 87, 90, 85, 0]
let filledArray = fillingEmpValues(dataArray: array) // [83, 83, 83, 87, 87, 87, 90, 85, 85]

Answer 2

I might suggest using reduce(into:):
let array = [70, 75, 0, 0, 0, 87, 90, 85, 0]
let array2 = array.reduce(into: [Int]()) { (result, value) in
if value == 0 {
result.append(result.last ?? 0)
} else {
result.append(value)
}
}
Yielding:
[70, 75, 75, 75, 75, 87, 90, 85, 85]