Read size invalid argument - expected data input? about glow HOT 7 CLOSED

package main

import (
	"flag"
	"fmt"

	"bitbucket.org/myapp/db"
	"bitbucket.org/myapp/model"
	"bitbucket.org/myapp/ptmath"

	_ "github.com/chrislusf/glow/driver"
	_ "github.com/chrislusf/glow/flow"
)

//GroupResult - grouping result
type GroupResult struct {
	Leader    *model.PtSet
	GroupSize int
}

//Group2Test - input for grouping test
type Group2Test struct {
	LeaderCandidate *model.PtSet
	PtSet           []model.PtSet
}

func main() {
	flag.Parse()

	//get PointSets from DB
	ptSets := db.GetAvailablePointSets()

	//Convert points to a different Coordinate System before running analysis:
	for idx, ptSet := range ptSets {
		conversionMatrix := ptmath.GetConversionMatrix(ptSet)
		var xyzSlice []model.XyzPt
		for _, pt := range ptSet.PtSourceSlice {
			xyz := ptmath.CalculateXYZ(*conversionMatrix, pt)
			xyzSlice = append(xyzSlice, *xyz)
		}
		ptSets[idx].xyzSlice = xyzSlice
	}

	//map reduce method to find biggest group:
	bestGroupLeader := loadCadidates(ptSets)
	fmt.Println("\nBest candidate ID:", winner.LeaderCandidate.ID, ", GroupSize: ", winner.GroupSize)

}

var (
	f       = flow.New()
	flowOut = make(chan GroupResult)
)

func loadCadidates(ptSets []model.PtSet) *GroupResult {
	var bestCandidate *GroupResult

	f.Source(func(out chan Group2Test) {
		ptSetIdx := 0
		for ptSetIdx < len(ptSets) {
			out <- Group2Test{&ptSets[ptSetIdx], ptSets}
			ptSetIdx++
		}
	}, /*len(ptSets)*/ 10).Map(func(g2Test Group2Test) GroupResult {
		return loadCandidateGroupSize(g2Test.LeaderCandidate, g2Test.PtSet)
	}).Reduce(func(x GroupResult, y GroupResult) GroupResult {
		//find the largest group:
		if x.GroupSize > y.GroupSize {
			return x
		} //else
		return y
	}).Map(func(winner GroupResult) {
		fmt.Println("\nBest ID:", winner.LeaderCandidate.ID, ", GroupSize: ", winner.GroupSize)
		bestCandidate = &winner
	}).Run()

	return bestCandidate
}

func loadCandidateGroupSize(leaderCandidate *model.PtSet, ptSets []model.PtSet) GroupResult {
	//count how many point sets have all points within some distance of a leaderCandidate
	setSize := len(leaderCandidate.xyzSlice)
	limit := 5
	groupSize := 0

	for _, ptSet := range ptSets {
		idx := 0
		maxDist := 0
		for idx < setSize {
			ptDist = ptmath.Distance(ptSet.xyzSlice[idx], leaderCandidate.xyzSlice[idx])
			if ptDist > maxDist {
				maxDist = ptDist
			}
			idx++
		}
		if maxDist < limit {
			groupSize++
		}
	}
	res := GroupResult{}
	res.LeaderCandidate = leaderCandidate
	res.GroupSize = groupSize
	return res
}