find the variance of all keys in a map in ruby

To find the variance of all keys in a map or hash in Ruby, we first need to calculate the mean. Once we have calculated the mean, we can use it to calculate the variance.

Here is an example code snippet:

main.rb
# Sample map
map = { a: 1, b: 2, c: 3, d: 4, e: 5 }

# Calculate the mean
mean = map.keys.reduce(0.0, :+) / map.size

# Calculate the variance
variance = map.keys.inject(0) { |variance, key| variance + (key - mean) ** 2 } / map.size

puts "Mean: #{mean}"
puts "Variance: #{variance}"
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In this example, we first create a map with some sample keys and values. We then calculate the mean by summing all the keys and dividing by the size of the map.

Next, we calculate the variance by iterating over each key in the map, subtracting the mean, and squaring the result. We then sum up all the squared differences and divide by the size of the map.

Finally, we output the mean and variance using puts. This code should output:

main.rb
Mean: 3.0
Variance: 2.0
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Note that we use inject(0) to initialize a variable variance to zero and then add to it in each iteration.