find the variance of all keys in a map in swift

To find the variance of all keys in a Swift map, we'll need to do the following steps:

1. Calculate the mean of all the keys
2. Calculate the sum of the squared differences between each key and the mean
3. Divide the sum by the number of keys minus 1.

Here's the Swift code to do this:

main.swift
var map: [Int: Double] = [1: 12.0, 2: 21.0, 3: 18.0, 4: 23.0, 5: 15.0]

// Step 1: Calculate the mean
let mean = Double(map.keys.reduce(0, +)) / Double(map.count)

// Step 2: Calculate the sum of the squared differences
var sumOfSquaredDifferences = 0.0
for key in map.keys {
    let difference = Double(key) - mean
    sumOfSquaredDifferences += difference * difference
}

// Step 3: Calculate the variance
let variance = sumOfSquaredDifferences / Double(map.count - 1)

print(variance)
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In this example, we created a map with integer keys and double values. We first calculated the mean of all the keys using the reduce method and calculated the sum of the squared differences between each key and the mean using a for loop. Finally, we divided the sum by the count of keys minus one to get the variance.