I had two Arrays.
let quntityArr = ["1","3","4","7"]
let priceArr = ["£129.95", "£179.95","£169.95","£199.85"]
I want to multiply these both Arrays in the following way
let totalArr = ["1*£129.95", "3*£179.95", "4*£169.95", "7*£199.85"]
Here I want to calculate each price with those product quantities.
You need
let quntityArr:[Double] = [1,3,4,7]
let priceArr = [129.95, 179.95,169.95,199.85]
let totalArr = zip(quntityArr, priceArr).map { "£\($0 * $1)" }
print(totalArr)
Assuming your input data is provided as array of String.
1. Input Data
let quntityArr = ["1","3","4","7"]
let priceArr = ["£129.95", "£179.95","£169.95","£199.85"]
2. Convert input data in array of Int and Double
let quantities = quntityArr
.compactMap(Int.init)
let prices = priceArr
.map { $0.dropFirst() }
.compactMap (Double.init)
3. Verify no input value has been discarded
assert(quntityArr.count == quantities.count)
assert(priceArr.count == prices.count)
4. Do the math
let results = zip(quantities, prices).map { Double($0) * $1 }.map { "£\($0)"}
5. Result
["£129.95", "£539.8499999999999", "£679.8", "£1398.95"]
Related
I have an array that describes a list of auto parts (Swift/IOS,array already in such structure arrived from other source.):
let parts = [
"Wheel = 230$",
"Door = 200$",
"Wheel = 300$",
"Seat = 150$",
"Seat = 150$",
"Rugs = 100$"]
I need to calculate the sum of the prices of the auto parts for each type of part. Here's the result I'm looking for:
let expectedResult = [
"wheel 530$",
"Door 200$",
"Seat 300$",
"Rugs 100$"
]
I don’t understand how to do it.
Here is a solution where I loop through the array and split each element on "=" and then sum the values together using a dictionary. Once that is done the dictionary is converted back to an array
let parts = [
"Wheel = 230$",
"Door = 200$",
"Wheel = 300$",
"Seat = 150$",
"Seat = 150$",
"Rugs = 100$"]
var values = [String: Int]() // Used to calculate totals per part
parts.forEach { string in
let split = string.split(separator: "=")
// Make sure the split worked as expected and that we have an integer value after the =
guard split.count == 2,
let value = Int(String(split[1]).trimmingCharacters(in: .whitespaces).dropLast()) else { return }
let key = String(split[0]).trimmingCharacters(in: .whitespaces)
// Sum values over the part name
values[key, default: 0] += value
}
// Convert back to an array of strings
let output = values.map { "\($0.key) \($0.value)$"}
print(output)
Re:
Finding a value in an array of arrays (similar to VLOOKUP function in Excel) in Swift
The above shows a method for determining the next lowest value in a 2D array given a search value. Reproduced here for convenience:
let testArray: [[Double]] = [
[0,0],
[1000,20.5],
[3000,21],
[3500,22.5],
[3300,21],
]
let income: Double = 3500
var closest = testArray[0][0]
var closestDif = closest - income
for innerArray in testArray {
let value = innerArray[0]
let thisDif = value - income
guard thisDif <= 0 else {
continue
}
if closestDif < thisDif {
closestDif = thisDif
closest = value
guard closestDif != 0 else {
break
}
}
}
print(closest)
The value returned for closest is 3500. Can someone please describe how we then retrieve the corresponding second number in the array [3500, 22.5] i.e. 22.5?
(edit)
Is enumerated(){....} a cleaner way to do this?
Thanks!
You can easily modify Martin R's answer from the linked Q&A to keep the whole inner array in compactMap and then find the maximum based on the first element of each inner array.
let result = testArray.compactMap { $0[0] <= income ? $0 : nil }.max(by: {$0.first! < $1.first!})! // [3500, 22.5]
#David Pasztor thanks your solution works nicely. I’m working swift 3 so I had to substitute “flatMap” for "compactMap" but otherwise it works great and just one line of code! I have used the same technique to also obtain the nearest higher values in the data to the search value (income) and then interpolate to get a value in the second column proportional to the search value income. The interpolation requires guarding against divide by zero when the search value income equals one of the values in the first column in which case the corresponding result0[0],[1] and result1[0],[1] are identical.
let testarray:[[Double]] = [
[0,0],
[1000,20.5],
[3000,21],
[3500,22.5],
[3300,21],
]
let income:Double = 3400
let result0 = testarray.flatMap { $0[0] <= income ? $0 : nil }.max(by: {$0.first! < $1.first!})!
let result1 = testarray.flatMap { $0[0] >= income ? $0 : nil }.min(by: {$0.first! < $1.first!})!
if income - result0[0] < 0.001 {
let interp = result0[1]
print(interp)
}
else {
let interp = result0[1] + (result1[1] - result0[1])*(income - result0[0])/(result1[0] - result0[0])
print(interp) // 21.75
}
I have 2 arrays, both of kind [[String:Any]] , where each element :
["date":Date,"value":CGFloat] //always looks like this
I might even have more than 2 (!)
I would like to create a single array with the same structure that sums all of them (2 or more) for each date that appears in all of them.
If the date of array1 does not appear on the others(array2, etc) I will simply add 0 to the value at array 1 for this specific date.
Is there a simple efficient way to do so ?
Instead of dictionaries use structs, it's more convenient:
struct MyStruct {
let date: Date
let value: CGFloat
}
Let's create 3 arrays of MyStructs:
let now = Date()
let later = now.addingTimeInterval(3600)
let earlier = now.addingTimeInterval(-3600)
let array1: [MyStruct] = [MyStruct(date: now, value: 1),
MyStruct(date: later, value: 2)]
let array2: [MyStruct] = [MyStruct(date: now, value: 3),
MyStruct(date: later, value: 4)]
let array3: [MyStruct] = [ MyStruct(date: earlier, value: 5),
MyStruct(date: later, value: 6)]
Now, let's group the elements and add the values for the elements with the same date property:
let allArrays = array1 + array2 + array3
let dict = Dictionary(allArrays.map { ($0.date, $0.value) },
uniquingKeysWith: { $0 + $1 })
All you have to do now is convert it back to an array of MyStruct:
let newArray = dict.map { MyStruct(date: $0.key, value: $0.value) }
And you can check the results like so:
for element in newArray {
print("date =", element.date, "value =", element.value)
}
I found a way, assuming data is inside a structure(not a dic) which is a better practice.
I will put all arrays into a single large array, sort it by dates, loop on it and as long as date is equal previous date(or close enough to equality), I will sum the values up. When the next date is different, I will save the date and the sum.
//create a combined array from all given arrays
var combined = [RootData]()
for list in dataSets {combined.append(contentsOf: list)}
//sort it by dates
let sortedArray = combined.sorted { $0.date < $1.date }
//new array - sum of all
var sumData = [RootData]()
var last:Date = sortedArray[0].date //set starting point
var sum:CGFloat = 0
for element in sortedArray
{
//same date - accumulate(same is less than 1 sec difference)
if(abs(element.date.seconds(from: last)) <= 1) {
sum+=element.value
}
//save
else {
sumData.append(RootData(value:sum,date:last))
sum=element.value
}
last=element.date
}
//last object
sumData.append(RootData(value:sum,date:last))
return averageData
Here RootData is a simple structure for the data with :
value:CGFloat
date:Date
Works as expected.
Because dates are not always completely equal , I check equality by assuming 1 second or less is the same date.
I am trying to change my string value in an array after shuffling another array, how am i to do this?
Example:
var array1 = [1,2,3,4,5,6]
var stringarray = ["\\(array1[0]) = 1")
array1.shuffle()
print(stringarray)
How am i to change the original stringarray value to the new shuffled value?
Thank you
The task:
#IBAction func nextQuestion(_ sender: Any) {
if levelSelected == 1 {
questionLabel.text = standardRules.randomElement()
}
players.shuffle()
print(players)
standardRules has a string value that takes the value of players[0]
Essentially what i am trying to do is this:
I am trying to grab 2 random values that are not the same in a string like this
var players = ["Jack, John, Michael, Peter"]
var playersArray = ["\(players.randomElement) and \(players.randomElement) has to battle")
How am i to do this, so it grabs 2 different values?
You could make it very easy by this code :
var players = ["Jack", "John", "Michael", "Peter"]
// get the first random element
var random1 = players.randomElement()
//delete that element so you can't duplicate it
players = players.filter{$0 != random1}
//get your second radom element
var random2 = players.randomElement()
//add your element again
players.append(random1!)
Looks like you're missing some core concepts of the Swift language. When you create your stringarray it makes a call of array1.description and stores the result into an array. From that point any modifications of the original array will not change anything in stringarray.
So if you want to pick two different players from an array you need to do something like that:
let index1 = Int.random(in: (0 ..< players.count))
var index2: Int
repeat {
index2 = Int.random(in: (0 ..< players.count))
} while index1 == index2
let matchText = "\(players[index1]) and \(players[index2] has to battle)"
I would try replacing:
var stringarray = ["\\(array1[0]) = 1")
array1.shuffle()
with:
var stringarray = array1.shuffle()
I am trying to dynamically chop an array of letters but I can't seem to reconvert the result back into a [String]
let letters:String = "abcdefghijklmnopqrstuvwxyz"
let lettersarray = Array(letters.characters)
var targetNum = 14 // Show just the first 14 characters
var resultsArray = [String]()
let resultsSlice = lettersarray.dropLast(lettersarray.count - targetNum) // Returns an Array Slice instead of an Array
let newresultsArray = Array(resultsSlice) // Returns Array<_element> instead of [String]
How do I return a [String] ie ["a","b","c"... eg]
You need to map the Character array back to String
let resultsArray = lettersarray.dropLast(lettersarray.count - targetNum).map{String($0)}
alternatively (credits to Leo Dabus)
let letters = "abcdefghijklmnopqrstuvwxyz"
let targetNum = 14
let resultsArray = letters.characters.prefix(targetNum).map{String($0)}
No need for an array here. It's hard to understand what you're trying to do, but if you just want the first 14 characters of a string, use the prefix method:
let s = String("abcdefghijklmno".characters.prefix(14))
Assuming that you are getting a String and want an array of characters which is a slice of characters from that String, you could use Swift's Half-Open Range Operator found here.
let letters:String = "abcdefghijklmnopqrstuvwxyz"
let lettersArray = Array(letters.characters)
let targetNum = 2
let resultsArray = lettersArray[0..<targetNum]
This will give you an ArraySlice<Character>. If you want an Array<Character> you could do this:
let resultsArray:Array<Character> = Array(lettersArray[0..<targetNum]) // ["a","b"]