splitting an array into subarrays by variables value

Question

I have an array of ages.

I want to split the array in to 4 subarrays by the age value.

A -> 0...25

B -> 26...50

c -> 51...75

d -> 76 +

I have no problem iterating through the array and append to different arrays by the age value.

            let subArrays: [[Int]] = [[], [], [], []]
            for age in ages {
                switch age {
                case 0...25:
                    subArrays[0].append(age)
                case 26...50:
                    subArrays[1].append(age)
                case 51...75:
                    subArrays[2].append(age)
                default:
                    subArrays[3].append(age)
                }
            }

My questions is: Is there a cleaner way to do this using map, split or any other function.

Thanks

Is it safe to assume you meant d -> 76+ instead of d -> 85+? — rmaddy
– rmaddy, Commented Feb 27, 2017 at 0:47

rmaddy · Accepted Answer · 2017-02-27 00:53:47Z

3

This doesn't use map or anything fancy but you can easily eliminate the switch:

var subArrays: [[Int]] = [[], [], [], []]
for age in ages {
    subArrays[min((age - 1) / 25, 3)].append(age)
}

The use of min ensures all values of 76 and greater go into the last slot.

And to test, with all boundary cases, try:

let ages = [ 50, 67, 75, 76, 25, 12, 26, 51, 99, 45, 0, 120, 16 ]

And then:

print(subArrays)

Gives:

[[25, 12, 0, 16], [50, 26, 45], [67, 75, 51], [76, 99, 120]]

edited Feb 27, 2017 at 0:53

answered Feb 27, 2017 at 0:47

rmaddy

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3 Comments

l'L'l Over a year ago

* no floats or negative numbers I assume.

rmaddy Over a year ago

@l'L'l The OP's code shows the results being an array of Int so I assume the array of ages are also Int. And nobody has a negative age. But my answer actually puts values from -23 to -1 in the first result array.

l'L'l Over a year ago

True, although depending on how you look at it some scientists might argue someone (not living) could be 11,000 years old too... but maybe that's way off for this question :)

Code Different · Accepted Answer · 2017-02-27 00:57:43Z

2

A more generic version that does not depend on any mathematical property of your ranges:

func split<T>(array: [T], ranges: [CountableClosedRange<T>]) -> [[T]] {
    var result = Array(repeating: [T](), count: ranges.count)

    for element in array {
        if let subIndex = ranges.index(where: { $0 ~= element }) {
            result[subIndex].append(element)
        }
    }
    return result
}

let ages = [10, 20, 30, 40, 50, 60]
let subarrays = split(array: ages, ranges: [0...25, 26...50, 51...75, 76...Int.max])

Note that it does not check for overlapping ranges.

answered Feb 27, 2017 at 0:57

Code Different

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1 Comment

rmaddy Over a year ago

You would need to pass in better ranges to handle floating point ages if that were desired. The sample ranges would't catch 25.5, for example, if an array of Float ages were used. I only mention this since the goal of your answer is to handle other types.

Eendje · Accepted Answer · 2017-02-27 02:29:36Z

0

Based on rmaddy's answer (practically the same) but within one line:

let subs = (0...3).map { sub in ages.filter { sub == min(($0 - 1) / 25, 3) } }

answered Feb 27, 2017 at 2:29

Eendje

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1 Comment

rmaddy Over a year ago

This is kind of slick but it is hard to read and understand and it ends up iterating the ages array 4 times instead of just once.

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