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main.go

main.go - Overview​

This file implements a command-line tool that calculates the histogram quantile based on input from stdin. It reads lines containing bucket upper bounds, bucket counts, and a quantile value, then calculates and prints the quantile using the bucketQuantile function (adapted from prometheus).

Detailed Documentation​

bucket struct​

type bucket struct {
	upperBound float64
	count      float64
}
  • Purpose: Represents a single bucket in a histogram.
    • upperBound: The upper bound of the bucket.
    • count: The number of observations in the bucket.

buckets type​

type buckets []bucket
  • Purpose: Represents a slice of bucket structs, used for sorting.

buckets.Len​

func (b buckets) Len() int { return len(b) }
  • Purpose: Returns the length of the buckets slice.
  • Returns: The length of the buckets slice as an int.

buckets.Swap​

func (b buckets) Swap(i, j int) { b[i], b[j] = b[j], b[i] }
  • Purpose: Swaps the elements at indices i and j in the buckets slice.
  • Parameters:
    • i: The index of the first element to swap (int).
    • j: The index of the second element to swap (int).
  • Returns: None.

buckets.Less​

func (b buckets) Less(i, j int) bool { return b[i].upperBound < b[j].upperBound }
  • Purpose: Compares the upper bounds of the buckets at indices i and j.
  • Parameters:
    • i: The index of the first bucket to compare (int).
    • j: The index of the second bucket to compare (int).
  • Returns: True if the upper bound of the bucket at index i is less than the upper bound of the bucket at index j; otherwise, false (bool).

bucketQuantile​

func bucketQuantile(q float64, buckets buckets) float64
  • Purpose: Calculates the quantile 'q' based on the given buckets.
  • Parameters:
    • q: The quantile to calculate (float64).
    • buckets: A slice of bucket structs representing the histogram (buckets).
  • Returns: The calculated quantile value (float64). Returns NaN or +/-Inf in special cases.

coalesceBuckets​

func coalesceBuckets(buckets buckets) buckets
  • Purpose: Merges buckets with the same upper bound.
  • Parameters:
    • buckets: A slice of bucket structs representing the histogram (buckets).
  • Returns: A new slice of buckets with adjacent buckets having the same upper bound merged (buckets).

ensureMonotonic​

func ensureMonotonic(buckets buckets)
  • Purpose: Ensures that the bucket counts increase monotonically with increasing upper bound.
  • Parameters:
    • buckets: A slice of bucket structs representing the histogram (buckets).
  • Returns: None. Modifies the input buckets slice in place.

readLines​

func readLines() []string
  • Purpose: Reads lines from standard input.
  • Returns: A slice of strings, where each string is a line read from stdin ([]string).

main​

func main()
  • Purpose: Main function of the program. Reads input from stdin, parses it, calculates the histogram quantile, and prints the result to stdout.
  • Parameters: None
  • Returns: None

Code Examples​

N/A

Clarity and Accuracy​

The documentation accurately reflects the code's functionality.

Include in Getting Started: NO