# Chapter 10 HIITFit challenge folder

**URL:** <https://forums.kodeco.com/t/chapter-10-hiitfit-challenge-folder/157606>\
**Category:** SwiftUI Apprentice\
**Created:** [November 16, 2021, 10:04pm UTC](https://forums.kodeco.com/t/chapter-10-hiitfit-challenge-folder/157606 "2021-11-16T22:04:15Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![supernova2108](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/supernova2108/32/81494_2.png) [@supernova2108](https://forums.kodeco.com/u/supernova2108)\
**Post date:** [November 16, 2021, 10:04pm UTC](https://forums.kodeco.com/t/chapter-10-hiitfit-challenge-folder/157606/1 "2021-11-16T22:04:15Z")

</div>

Hi. So I have been following along the excellent tutorial until Chapter 10 when we are asked to do the challenge to fix the design of HIITFit. The project supplied in the challenge directory contains some new code that I especially do not understand and I was hoping for some clarification.  
My question is on the code that was written in the .onAppear modifier, I will paste it below. I was adding my own comments to better understand what is going on

var body: some View {  
GeometryReader { geometry in  
VStack {  
HStack {  
ForEach(0…\<7) { index in  
bar(day: index, size: geometry.size)  
}  
}  
Divider()  
Spacer()  
}  
.onAppear {  
days = Date().lastSevenDays //array of dates from past week  
exercisesForWeek = ExerciseDay  
let counts: [Int] = days.map { day in  
let foundDate = exercisesForWeek.filter {  
$0.date.yearMonthDay == day.yearMonthDay  
}  
return foundDate.first?.exercises.count ?? 0  
//returns the number of exercises completed for the first day  
}  
assert(counts.count == 7)  
// remap values to 0 to maxBarHeight  
let maxValue = max(counts.max() ?? 0, 1)  
countsForWeek = counts.map {  
$0 \* maxBarHeight / maxValue  
}  
}

I understand that foundDate is an array of ExerciseDays, an array of exercises that were completed in the past week, and that counts as an array of integers, is an array of the number of exercises that were completed in the first day, the first ExerciseDay element

return foundDate.first?.exercises.count ?? 0

My question is, what is the purpose of counts as a value, since it is the number of exercises done on the first day? And given that our development data does not have 7 exercises, what is the purpose of the assert line?

assert(counts.count == 7)

The assertion is going to fail every time, and I am positively flummoxed as to the logic behind this code. Any help would be appreciated, if I hope to reproduce what I have learnt in an app of my own I feel I have to understand the logic behind the supplied code.

> <https://github.com/raywenderlich/suia-materials/blob/editions/1.0/10-refining-your-app/projects/challenge/HIITFit/HIITFit/Views/HistoryBarView.swift>

Thanks in advance

---

<div class="post-metadata">

**Author:** ![caroline](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/caroline/32/111867_2.png) [@caroline](https://forums.kodeco.com/u/caroline)\
**Post date:** [November 17, 2021, 1:56am UTC](https://forums.kodeco.com/t/chapter-10-hiitfit-challenge-folder/157606/2 "2021-11-17T01:56:59Z")

</div>

Hi @supernova2108, and welcome to the forum 😃 !

You can format your code blocks using a backtick `

Use three of them before and after the code block

````auto
This is a code block surrounded by ```

````

It means that the post renderer won’t try and do clever things, for example, it lost the important line:

```auto
exercisesForWeek = [ExerciseDay](history.exerciseDays.prefix(7))

```

As for your question, I hope I can resolve the confusion.

Going through the code:

**`days`** is an array that contains seven dates for the last seven days. eg `[2021-11-11, 2021-11-12, ...., 2021-11-17]`

**`exercisesForWeek`** is an array that contains a maximum of seven exercises in the format:

```auto
id: BE209DAC-CC72-42FA-B01B-80DB3CF50D09, 
date: 2021-11-17 01:18:04 +0000, 
exercises: ["Step Up"]

```

The chart drawing is easier if there are always seven data points for the week, one for the count of each day, but if you’ve only done one exercise, then you only have one data point.

So in an ideal world, `counts` will contain seven entries and then the chart drawing is easier. That’s what the `assert` does - it makes sure there are seven entries in `counts`.

```auto
let counts: [Int] = days.map { day in
}

```

This code will iterate through `days`. We already know that there are seven entries in `days`, so there will be seven iterations, each using `day`. Therefore `counts` will end up having seven entries.

```auto
let foundDate = exercisesForWeek.filter {
   $0.date.yearMonthDay == day.yearMonthDay
}

```

Here you filter `exercisesForWeek` so that `foundDate` is an array that contains only the exercises performed on the `day` currently being processed in the `map` loop.

If there are no entries for a particular day, then `foundDate` will be empty, otherwise it will contain the single `ExerciseDay` for that day.

```auto
return foundDate.first?.exercises.count ?? 0

```

You then get the first entry in `foundDate`. If `foundDate` is empty, then there is no first entry. In that case, the zero after the `??` is returned.  
Otherwise, the first entry’s count of exercises performed is returned.

It’s quite complex Swift code. An alternative, less Swifty code would be:

```auto
var counts: [Int] = []
for day in days {
   var countForDay = 0
   for exerciseDay in exercisesForWeek {
      if exerciseDay.date.yearMonthDay == day.yearMonthDay {
         countForDay = exerciseDay.exercises.count
      }
    }
  counts.append(countForDay)
}

```

This code is perfectly acceptable. However, variables rather than constants are inherently unsafe, as at any time you can write to `counts`. In a longer piece of code, you might not pick up that you are writing to `counts` when you’re not supposed to.

That’s why `let counts = days.map...` is preferred to the `for` loop and appending to `counts`.

I hope that helps - if you’re still confused, please ask further questions.

---

<div class="post-metadata">

**Author:** ![shogunkaramazov](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/shogunkaramazov/32/108826_2.png) [@shogunkaramazov](https://forums.kodeco.com/u/shogunkaramazov)\
**Post date:** [November 17, 2021, 5:19am UTC](https://forums.kodeco.com/t/chapter-10-hiitfit-challenge-folder/157606/3 "2021-11-17T05:19:29Z")

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@supernova2108 Please definitely check out the following Swift tutorials when you actually get a chance in order to understand even better how both `map(_:)` and `filter(_:)` really work under the hood after all:

> **[Imperative programming vs Functional programming – a Beginner’s approach Part...](https://cosminpupaza.wordpress.com/2015/10/28/imperative-programming-vs-functional-programming-a-beginners-approach-part-1-map/)**
>
> Learn all you need to know about imperative programming vs functional programming in Swift.

> **[Imperative programming vs Functional programming – a Beginner’s approach...](https://cosminpupaza.wordpress.com/2015/11/02/imperative-programming-vs-functional-programming-a-beginners-approach-part-2-filter/)**
>
> Learn all you need to know about imperative programming vs functional programming in Swift.

I really do hope they help!