This program takes the XML file from iPhone's Health app (Health -> User -> Export data) and converts it into a CSV file with max, min, avg, p75 & p90 heart rate.

healthkit-data-to-csv.go

package main

import (
	"encoding/csv"
	"encoding/xml"
	"flag"
	"fmt"
	"io/ioutil"
	"os"
	"sort"
	"strconv"
	"time"
)

type Record struct {
	XMLName       xml.Name `xml:"Record"`
	Text          string   `xml:",chardata"`
	Type          string   `xml:"type,attr"`
	SourceName    string   `xml:"sourceName,attr"`
	SourceVersion string   `xml:"sourceVersion,attr"`
	Device        string   `xml:"device,attr"`
	Unit          string   `xml:"unit,attr"`
	CreationDate  string   `xml:"creationDate,attr"`
	StartDate     string   `xml:"startDate,attr"`
	EndDate       string   `xml:"endDate,attr"`
	Value         string   `xml:"value,attr"`
}

type ByValue []Record

func (b ByValue) Len() int {
	return len([]Record(b))
}

func (b ByValue) Less(i, j int) bool {
	recs := []Record(b)
	lhs, err := strconv.Atoi(recs[i].Value)
	if err != nil {
		return true
	}
	rhs, err := strconv.Atoi(recs[j].Value)
	if err != nil {
		return false
	}
	return lhs < rhs
}

func (b ByValue) Swap(i, j int) {
	recs := []Record(b)
	recs[i], recs[j] = recs[j], recs[i]
	b = ByValue(recs)
}

type HealthData struct {
	XMLName xml.Name `xml:"HealthData"`
	Records []Record `xml:"Record"`
}

type CSVRec struct {
	Day time.Time
	Max string
	Min string
	Avg string
	P90 string
}

func main() {
	flag.Parse()
	args := flag.Args()
	if len(args) != 1 {
		fmt.Println("please provide file to parse")
		os.Exit(1)
	}
	file := args[0]
	fh, err := os.Open(file)
	if err != nil {
		fmt.Println("unable to open file:", file)
		os.Exit(1)
	}

	data, err := ioutil.ReadAll(fh)
	if err != nil {
		fmt.Println("unable to read file", file)
		os.Exit(1)
	}
	var hd HealthData
	err = xml.Unmarshal(data, &hd)

	if err != nil {
		fmt.Println("unable to unmarshal file", err)
		os.Exit(1)
	}

	dayRate := map[time.Time][]Record{}

	for _, rec := range hd.Records {
		if rec.Type != "HKQuantityTypeIdentifierHeartRate" {
			continue
		}
		recStart, err := time.Parse("2006-01-02 15:04:05 -0700", rec.StartDate)
		if err != nil {
			fmt.Println("ignoring rec:", rec)
			continue
		}
		day := time.Date(recStart.Year(), recStart.Month(), recStart.Day(), 0, 0, 0, 0, time.Local)
		if exRec, ok := dayRate[day]; ok {
			dayRate[day] = append(exRec, rec)
		} else {
			dayRate[day] = []Record{rec}
		}
	}
	csvRecs := [][]string{
		{"day", "max", "min", "avg", "p75", "p90"},
	}
	for day, recs := range dayRate {
		sort.Sort(ByValue(recs))
		p90 := int(0.9 * float32(len(recs)))
		p75 := int(0.75 * float32(len(recs)))
		fmt.Println("Day:", day.Year(), day.Month(), day.Day(),
			"->",
			"Max:", recs[len(recs)-1].Value,
			"Min:", recs[0].Value,
			"Avg:", recs[len(recs)/2].Value,
			"P75", recs[p75].Value,
			"P90", recs[p90].Value,
		)

		csvRecs = append(csvRecs, []string{
			fmt.Sprintf("%d/%s/%d", day.Year(), day.Month().String(), day.Day()),
			recs[len(recs)-1].Value,
			recs[0].Value,
			recs[len(recs)/2].Value,
			recs[p90].Value,
		})
	}

	out, err := os.OpenFile("prosessed.csv", os.O_RDWR|os.O_CREATE, 0755)
	if err != nil {
		out = os.Stdout
	}
	csv.NewWriter(out).WriteAll(csvRecs)
}