diff --git a/pkg/obialign/fastlcsegf.go b/pkg/obialign/fastlcsegf.go
index d59ac46..bce5d06 100644
--- a/pkg/obialign/fastlcsegf.go
+++ b/pkg/obialign/fastlcsegf.go
@@ -4,33 +4,6 @@ import (
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiseq"
 )
 
-var _iupac = [26]byte{
-	//  a   b  c  d   e  f
-	1, 14, 2, 13, 0, 0,
-	//  g   h  i  j  k   l
-	4, 11, 0, 0, 12, 0,
-	//  m   n  o  p  q  r
-	3, 15, 0, 0, 0, 5,
-	//  s  t  u   v  w  x
-	6, 8, 8, 13, 9, 0,
-	//  y   z
-	10, 0,
-}
-
-func _samenuc(a, b byte) bool {
-	if (a >= 'A') && (a <= 'Z') {
-		a |= 32
-	}
-	if (b >= 'A') && (b <= 'Z') {
-		b |= 32
-	}
-
-	if (a >= 'a') && (a <= 'z') && (b >= 'a') && (b <= 'z') {
-		return (_iupac[a-'a'] & _iupac[b-'a']) > 0
-	}
-	return a == b
-}
-
 // FastLCSEGFScoreByte calculates the score of the Longest Common Subsequence (LCS) between two byte slices.
 //
 // The score is calculated using the following scoring matrix:
@@ -165,7 +138,7 @@ func FastLCSEGFScoreByte(bA, bB []byte, maxError int, endgapfree bool, buffer *[
 			default:
 				// We are in the middle of the matrix
 				Sdiag = _incpath(previous[x])
-				if _samenuc(bA[j-1], bB[i-1]) {
+				if obiseq.SameIUPACNuc(bA[j-1], bB[i-1]) {
 					Sdiag = _incscore(Sdiag)
 				}
 
@@ -265,7 +238,7 @@ func FastLCSEGFScoreByte(bA, bB []byte, maxError int, endgapfree bool, buffer *[
 				Sleft = _notavail
 			default:
 				Sdiag = _incpath(previous[x])
-				if _samenuc(bA[j-1], bB[i-1]) {
+				if obiseq.SameIUPACNuc(bA[j-1], bB[i-1]) {
 					Sdiag = _incscore(Sdiag)
 				}
 
diff --git a/pkg/obialign/locatepattern.go b/pkg/obialign/locatepattern.go
index 23b5538..d5170e6 100644
--- a/pkg/obialign/locatepattern.go
+++ b/pkg/obialign/locatepattern.go
@@ -1,6 +1,9 @@
 package obialign
 
-import log "github.com/sirupsen/logrus"
+import (
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiseq"
+	log "github.com/sirupsen/logrus"
+)
 
 // buffIndex converts a pair of coordinates (i, j) into a linear index in a matrix
 // of size width x width. The coordinates are (-1)-indexed, and the linear index
@@ -69,7 +72,7 @@ func LocatePattern(id string, pattern, sequence []byte) (int, int, int) {
 			// Mismatch score = -1
 			// Match score = 0
 			match := -1
-			if _samenuc(pattern[j], sequence[i]) {
+			if obiseq.SameIUPACNuc(pattern[j], sequence[i]) {
 				match = 0
 			}
 
@@ -103,7 +106,7 @@ func LocatePattern(id string, pattern, sequence []byte) (int, int, int) {
 		// Mismatch score = -1
 		// Match score = 0
 		match := -1
-		if _samenuc(pattern[jmax], sequence[i]) {
+		if obiseq.SameIUPACNuc(pattern[jmax], sequence[i]) {
 			match = 0
 		}
 
diff --git a/pkg/obioptions/version.go b/pkg/obioptions/version.go
index b326b22..76d4cf6 100644
--- a/pkg/obioptions/version.go
+++ b/pkg/obioptions/version.go
@@ -8,7 +8,7 @@ import (
 // corresponds to the last commit, and not the one when the file will be
 // commited
 
-var _Commit = "6d204f6"
+var _Commit = "29bf4ce"
 var _Version = "Release 4.4.0"
 
 // Version returns the version of the obitools package.
diff --git a/pkg/obiseq/iupac_nog.go b/pkg/obiseq/iupac_nog.go
new file mode 100644
index 0000000..a3fba9b
--- /dev/null
+++ b/pkg/obiseq/iupac_nog.go
@@ -0,0 +1,28 @@
+package obiseq
+
+var _iupac = [26]byte{
+	//  a   b  c  d   e  f
+	1, 14, 2, 13, 0, 0,
+	//  g   h  i  j  k   l
+	4, 11, 0, 0, 12, 0,
+	//  m   n  o  p  q  r
+	3, 15, 0, 0, 0, 5,
+	//  s  t  u   v  w  x
+	6, 8, 8, 13, 9, 0,
+	//  y   z
+	10, 0,
+}
+
+func SameIUPACNuc(a, b byte) bool {
+	if (a >= 'A') && (a <= 'Z') {
+		a |= 32
+	}
+	if (b >= 'A') && (b <= 'Z') {
+		b |= 32
+	}
+
+	if (a >= 'a') && (a <= 'z') && (b >= 'a') && (b <= 'z') {
+		return (_iupac[a-'a'] & _iupac[b-'a']) > 0
+	}
+	return a == b
+}
diff --git a/pkg/obitools/obiclean/chimera.go b/pkg/obitools/obiclean/chimera.go
index b13637a..fda821e 100644
--- a/pkg/obitools/obiclean/chimera.go
+++ b/pkg/obitools/obiclean/chimera.go
@@ -2,12 +2,10 @@ package obiclean
 
 import (
 	"fmt"
-	"os"
 	"sort"
 
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiseq"
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiutils"
-	"github.com/schollz/progressbar/v3"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -21,13 +19,13 @@ func commonPrefix(a, b *obiseq.BioSequence) int {
 	as := a.Sequence()
 	bs := b.Sequence()
 
-	for i < l && as[i] == bs[i] {
+	for i < l && obiseq.SameIUPACNuc(as[i], bs[i]) {
 		i++
 	}
 
-	if obiutils.UnsafeString(as[:i]) != obiutils.UnsafeString(bs[:i]) {
-		log.Fatalf("i: %d, j: %d (%s/%s)", i, i, as[:i], bs[:i])
-	}
+	// if obiutils.UnsafeString(as[:i]) != obiutils.UnsafeString(bs[:i]) {
+	// 	log.Fatalf("i: %d, j: %d (%s/%s)", i, i, as[:i], bs[:i])
+	// }
 
 	return i
 }
@@ -44,29 +42,97 @@ func commonSuffix(a, b *obiseq.BioSequence) int {
 	bs := b.Sequence()
 
 	l := 0
-	for i >= 0 && j >= 0 && as[i] == bs[j] {
+	for i >= 0 && j >= 0 && obiseq.SameIUPACNuc(as[i], bs[j]) {
 		i--
 		j--
 		l++
 	}
 
-	if obiutils.UnsafeString(as[i+1:]) != obiutils.UnsafeString(bs[j+1:]) {
-		log.Fatalf("i: %d, j: %d (%s/%s)", i, j, as[i+1:], bs[j+1:])
-	}
-	// obilog.Warnf("i: %d, j: %d (%s)", i, j, as[i+1:])
+	// if obiutils.UnsafeString(as[i+1:]) != obiutils.UnsafeString(bs[j+1:]) {
+	// 	log.Fatalf("i: %d, j: %d (%s/%s)", i, j, as[i+1:], bs[j+1:])
+	// }
+	// log.Warnf("i: %d, j: %d (%s)", i, j, as[i+1:])
 
 	return l
 }
 
+// oneDifference return true if s1 and s2 differ by exactly 1 operation
+// (substitution, insertion or deletion)
+func oneDifference(s1, s2 []byte) bool {
+	l1 := len(s1)
+	l2 := len(s2)
+
+	// Case 1: same lengths → test substitution
+	if l1 == l2 {
+		diff := 0
+		for i := 0; i < l1; i++ {
+			if s1[i] != s2[i] {
+				diff++
+				if diff > 1 {
+					return false
+				}
+			}
+		}
+		return diff == 1
+	}
+
+	// Case 2: difference of 1 character → insertion/deletion
+	if l1 == l2+1 {
+		for i := 0; i < l1; i++ {
+			if string(s1[:i])+string(s1[i+1:]) == string(s2) {
+				return true
+			}
+		}
+		return false
+	}
+	if l2 == l1+1 {
+		for i := 0; i < l2; i++ {
+			if string(s2[:i])+string(s2[i+1:]) == string(s1) {
+				return true
+			}
+		}
+		return false
+	}
+
+	// Case 3: difference > 1 character
+	return false
+}
+
+func GetChimera(sequence *obiseq.BioSequence) map[string]string {
+	annotation := sequence.Annotations()
+	iobistatus, ok := annotation["chimera"]
+	var chimera map[string]string
+	var err error
+
+	if ok {
+		switch iobistatus := iobistatus.(type) {
+		case map[string]string:
+			chimera = iobistatus
+		case map[string]interface{}:
+			chimera = make(map[string]string)
+			for k, v := range iobistatus {
+				chimera[k], err = obiutils.InterfaceToString(v)
+				if err != nil {
+					log.Panicf("chimera attribute of sequence %s must be castable to a map[string]string", sequence.Id())
+				}
+			}
+		}
+	} else {
+		chimera = make(map[string]string)
+		annotation["chimera"] = chimera
+	}
+
+	return chimera
+}
+
+// add the suffix/prefix comparisons to detect chimeras (handle IUPAC codes)
 func AnnotateChimera(samples map[string]*[]*seqPCR) {
 
 	w := func(sample string, seqs *[]*seqPCR) {
 		ls := len(*seqs)
-		cp := make([]int, ls)
-		cs := make([]int, ls)
-
 		pcrs := make([]*seqPCR, 0, ls)
 
+		// select only sequences without edges (head sequences)
 		for _, s := range *seqs {
 			if len(s.Edges) == 0 {
 				pcrs = append(pcrs, s)
@@ -75,66 +141,63 @@ func AnnotateChimera(samples map[string]*[]*seqPCR) {
 
 		lp := len(pcrs)
 
+		// sort by increasing weight (like increasing abundance)
 		sort.Slice(pcrs, func(i, j int) bool {
 			return pcrs[i].Weight < pcrs[j].Weight
 		})
 
 		for i, s := range pcrs {
-			for j := i + 1; j < lp; j++ {
-				s2 := pcrs[j]
-				cp[j] = commonPrefix(s.Sequence, s2.Sequence)
-				cs[j] = commonSuffix(s.Sequence, s2.Sequence)
-			}
+			seqRef := s.Sequence
+			L := seqRef.Len()
 
-			var cm map[string]string
-			var err error
+			maxLeft, maxRight := 0, 0
+			var nameLeft, nameRight string
 
-			chimera, ok := s.Sequence.GetAttribute("chimera")
+			// looking for potential parents
+			for j := 0; j < lp; j++ {
+				if j == i {
+					continue
+				}
+				seqParent := pcrs[j].Sequence
 
-			if !ok {
-				cm = map[string]string{}
-			} else {
-				cm, err = obiutils.InterfaceToStringMap(chimera)
-				if err != nil {
-					log.Fatalf("type of chimera not map[string]string: %T (%v)",
-						chimera, err)
+				// Check abundance: parent must be more abundant
+				if pcrs[j].Weight <= s.Weight {
+					continue
+				}
+
+				// Check edit distance (skip if only one diff, supposed to never happen)
+				if oneDifference(seqRef.Sequence(), seqParent.Sequence()) {
+					continue
+				}
+
+				// Common prefix
+				left := commonPrefix(seqRef, seqParent)
+				if left > maxLeft {
+					maxLeft = left
+					nameLeft = seqParent.Id()
+				}
+
+				// Common suffix
+				right := commonSuffix(seqRef, seqParent)
+				if right > maxRight {
+					maxRight = right
+					nameRight = seqParent.Id()
 				}
 			}
 
-			ls := s.Sequence.Len()
+			// Select parents with longuest prefix/suffix
+			// Condition prefix+suffix covers the sequence and sequence not include into parent
+			if maxLeft >= L-maxRight && maxLeft > 0 && maxRight < L {
 
-			for k := i + 1; k < lp; k++ {
-				for l := i + 1; l < lp; l++ {
-					if k != l && cp[k]+cs[l] == ls {
-						cm[sample] = fmt.Sprintf("{%s}/{%s}@(%d)",
-							pcrs[k].Sequence.Id(),
-							pcrs[l].Sequence.Id(),
-							cp[k])
-					}
-				}
-			}
-
-			if len(cm) > 0 {
-				s.Sequence.SetAttribute("chimera", cm)
+				chimeraMap := GetChimera(s.Sequence)
+				// overlap sequence
+				overlap := seqRef.Sequence()[L-maxRight : maxLeft]
+				chimeraMap[sample] = fmt.Sprintf("{%s}/{%s}@(%s)(%d)(%d)(%d)", nameLeft, nameRight, overlap, L-maxRight, maxLeft, len(overlap))
 			}
 		}
-
 	}
 
-	pbopt := make([]progressbar.Option, 0, 5)
-	pbopt = append(pbopt,
-		progressbar.OptionSetWriter(os.Stderr),
-		progressbar.OptionSetWidth(15),
-		progressbar.OptionShowIts(),
-		progressbar.OptionSetPredictTime(true),
-		progressbar.OptionSetDescription("[Chimera detection]"),
-	)
-
-	bar := progressbar.NewOptions(len(samples), pbopt...)
-
 	for sn, sqs := range samples {
 		w(sn, sqs)
-		bar.Add(1)
 	}
-
 }
diff --git a/pkg/obitools/obimatrix/obimatrix.go b/pkg/obitools/obimatrix/obimatrix.go
index a08a31c..0a77159 100644
--- a/pkg/obitools/obimatrix/obimatrix.go
+++ b/pkg/obitools/obimatrix/obimatrix.go
@@ -3,6 +3,7 @@ package obimatrix
 import (
 	"encoding/csv"
 	"os"
+	"slices"
 	"sort"
 	"sync"
 
@@ -11,41 +12,55 @@ import (
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obidefault"
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiiter"
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiseq"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitools/obicsv"
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obiutils"
 	"golang.org/x/exp/maps"
 )
 
-type MatrixData map[string]map[string]interface{}
+type MatrixData struct {
+	matrix        map[string]map[string]interface{}
+	attributes    map[string]map[string]interface{}
+	attributeList []string
+	naValue       string
+}
 
 // MakeMatrixData generates a MatrixData instance.
 //
 // No parameters.
 // Returns a MatrixData.
-func MakeMatrixData() MatrixData {
-	return make(MatrixData)
+func MakeMatrixData(naValue string, attributes ...string) MatrixData {
+	return MatrixData{
+		matrix:        make(map[string]map[string]interface{}),
+		attributes:    make(map[string]map[string]interface{}),
+		attributeList: slices.Clone(attributes),
+		naValue:       naValue,
+	}
 }
 
 // NewMatrixData creates a new instance of MatrixData.
 //
 // It does not take any parameters.
 // It returns a pointer to a MatrixData object.
-func NewMatrixData() *MatrixData {
-	m := make(MatrixData)
+func NewMatrixData(naValue string, attributes ...string) *MatrixData {
+	m := MakeMatrixData(naValue, attributes...)
 	return &m
 }
 
 // TransposeMatrixData transposes the MatrixData.
 //
 // It takes no parameters.
+// If the input matrix has attributes, they are lost.
+// A unique attribute "id" is added to store the column ids of the input matrix.
 // It returns a pointer to the transposed MatrixData.
 func (matrix *MatrixData) TransposeMatrixData() *MatrixData {
-	m := make(MatrixData)
-	for k, v := range *matrix {
+	m := MakeMatrixData(matrix.naValue, "id")
+	for k, v := range *&matrix.matrix {
 		for kk, vv := range v {
-			if _, ok := m[kk]; !ok {
-				m[kk] = make(map[string]interface{})
+			if _, ok := m.matrix[kk]; !ok {
+				m.matrix[kk] = make(map[string]interface{})
 			}
-			m[kk][k] = vv
+			m.matrix[kk][k] = vv
+			m.attributes[kk] = map[string]interface{}{"id": k}
 		}
 	}
 	return &m
@@ -58,11 +73,12 @@ func (matrix *MatrixData) TransposeMatrixData() *MatrixData {
 // Returns the pointer to the merged MatrixData.
 func (data1 *MatrixData) MergeMatrixData(data2 *MatrixData) *MatrixData {
 
-	for k := range *data2 {
-		if _, ok := (*data1)[k]; ok {
+	for k := range data2.matrix {
+		if _, ok := data1.matrix[k]; ok {
 			log.Panicf("Sequence Id %s exists at least twice in the data set", k)
 		} else {
-			(*data1)[k] = (*data2)[k]
+			data1.matrix[k] = data2.matrix[k]
+			data1.attributes[k] = data2.attributes[k]
 		}
 	}
 
@@ -77,21 +93,74 @@ func (data1 *MatrixData) MergeMatrixData(data2 *MatrixData) *MatrixData {
 //
 // Returns:
 // - *MatrixData: The updated MatrixData object.
-func (data *MatrixData) Update(s *obiseq.BioSequence, mapkey string) *MatrixData {
+func (data *MatrixData) Update(s *obiseq.BioSequence, mapkey string, strict bool) *MatrixData {
+
+	sid := s.Id()
+
+	if _, ok := data.matrix[sid]; ok {
+		log.Panicf("Sequence Id %s exists at least twice in the data set", sid)
+	}
 	if v, ok := s.GetAttribute(mapkey); ok {
 		if m, ok := v.(*obiseq.StatsOnValues); ok {
 			m.RLock()
-			(*data)[s.Id()] = obiutils.MapToMapInterface(m.Map())
+			data.matrix[sid] = obiutils.MapToMapInterface(m.Map())
 			m.RUnlock()
 		} else if obiutils.IsAMap(v) {
-			(*data)[s.Id()] = obiutils.MapToMapInterface(v)
+			data.matrix[sid] = obiutils.MapToMapInterface(v)
 		} else {
 			log.Panicf("Attribute %s is not a map in the sequence %s", mapkey, s.Id())
 		}
 	} else {
-		log.Panicf("Attribute %s does not exist in the sequence %s", mapkey, s.Id())
+		if strict {
+			log.Panicf("Attribute %s does not exist in the sequence %s", mapkey, s.Id())
+		}
+		data.matrix[sid] = make(map[string]interface{})
 	}
 
+	attrs := make(map[string]interface{}, len(data.attributeList))
+	for _, attrname := range data.attributeList {
+		var value interface{}
+		ok := false
+		switch attrname {
+		case "id":
+			value = s.Id
+			ok = true
+		case "count":
+			value = s.Count()
+			ok = true
+		case "taxon":
+			taxon := s.Taxon(nil)
+			if taxon != nil {
+				value = taxon.String()
+
+			} else {
+				value = s.Taxid()
+			}
+			ok = true
+		case "sequence":
+			value = s.String()
+			ok = true
+		case "quality":
+			if s.HasQualities() {
+				l := s.Len()
+				q := s.Qualities()
+				ascii := make([]byte, l)
+				quality_shift := obidefault.WriteQualitiesShift()
+				for j := 0; j < l; j++ {
+					ascii[j] = uint8(q[j]) + uint8(quality_shift)
+				}
+				value = string(ascii)
+				ok = true
+			}
+		default:
+			value, ok = s.GetAttribute(attrname)
+		}
+		if ok {
+			attrs[attrname] = value
+		}
+	}
+	data.attributes[sid] = attrs
+
 	return data
 }
 
@@ -101,6 +170,49 @@ func IMatrix(iterator obiiter.IBioSequence) *MatrixData {
 	waiter := sync.WaitGroup{}
 
 	mapAttribute := CLIMapAttribute()
+	attribList := make([]string, 0)
+
+	if obicsv.CLIPrintId() {
+		attribList = append(attribList, "id")
+	}
+
+	if obicsv.CLIPrintCount() {
+		attribList = append(attribList, "count")
+	}
+
+	if obicsv.CLIPrintTaxon() {
+		attribList = append(attribList, "taxon")
+	}
+
+	if obicsv.CLIPrintDefinition() {
+		attribList = append(attribList, "definition")
+	}
+
+	if obicsv.CLIPrintSequence() {
+		attribList = append(attribList, "sequence")
+	}
+
+	if obicsv.CLIPrintQuality() {
+		attribList = append(attribList, "qualities")
+	}
+
+	attribList = append(attribList, obicsv.CLIToBeKeptAttributes()...)
+
+	if obicsv.CLIAutoColumns() {
+		if iterator.Next() {
+			batch := iterator.Get()
+			if len(batch.Slice()) == 0 {
+				log.Panicf("first batch should not be empty")
+			}
+			auto_slot := batch.Slice().AttributeKeys(true, true).Members()
+			slices.Sort(auto_slot)
+			attribList = append(attribList, auto_slot...)
+			iterator.PushBack()
+		}
+	}
+
+	naValue := obicsv.CLINAValue()
+	strict := CLIStrict()
 
 	summaries := make([]*MatrixData, nproc)
 
@@ -109,7 +221,7 @@ func IMatrix(iterator obiiter.IBioSequence) *MatrixData {
 		for iseq.Next() {
 			batch := iseq.Get()
 			for _, seq := range batch.Slice() {
-				summary.Update(seq, mapAttribute)
+				summary.Update(seq, mapAttribute, strict)
 			}
 		}
 		waiter.Done()
@@ -117,11 +229,11 @@ func IMatrix(iterator obiiter.IBioSequence) *MatrixData {
 
 	waiter.Add(nproc)
 
-	summaries[0] = NewMatrixData()
+	summaries[0] = NewMatrixData(naValue, attribList...)
 	go ff(iterator, summaries[0])
 
 	for i := 1; i < nproc; i++ {
-		summaries[i] = NewMatrixData()
+		summaries[i] = NewMatrixData(naValue, attribList...)
 		go ff(iterator.Split(), summaries[i])
 	}
 
@@ -138,7 +250,7 @@ func IMatrix(iterator obiiter.IBioSequence) *MatrixData {
 }
 
 func CLIWriteCSVToStdout(matrix *MatrixData) {
-	navalue := CLINaValue()
+	navalue := CLIMapNaValue()
 	csvwriter := csv.NewWriter(os.Stdout)
 
 	if CLITranspose() {
@@ -147,33 +259,45 @@ func CLIWriteCSVToStdout(matrix *MatrixData) {
 
 	samples := obiutils.NewSet[string]()
 
-	for _, v := range *matrix {
+	for _, v := range matrix.matrix {
 		samples.Add(maps.Keys(v)...)
 	}
 
 	osamples := samples.Members()
 	sort.Strings(osamples)
-
-	columns := make([]string, 1, len(osamples)+1)
-	columns[0] = "id"
+	columns := make([]string, 0, len(osamples)+len(matrix.attributeList))
+	columns = append(columns, matrix.attributeList...)
 	columns = append(columns, osamples...)
 
+	header := slices.Clone(columns)
+
 	csvwriter.Write(columns)
+	nattribs := len(matrix.attributeList)
 
-	for k, data := range *matrix {
-		columns = columns[0:1]
-		columns[0] = k
-		for _, kk := range osamples {
-			if v, ok := data[kk]; ok {
-				vs, err := obiutils.InterfaceToString(v)
-				if err != nil {
-					log.Panicf("value %v in sequence %s for attribute %s cannot be casted to a string", v, k, kk)
+	for k, data := range matrix.matrix {
+		attrs := matrix.attributes[k]
+		for i, kk := range header {
+			if i < nattribs {
+				if v, ok := attrs[kk]; ok {
+					vs, err := obiutils.InterfaceToString(v)
+					if err != nil {
+						log.Panicf("value  %v in sequence %s for attribute %s cannot be casted to a string", v, k, kk)
+					}
+					columns[i] = vs
+				} else {
+					columns[i] = matrix.naValue
 				}
-				columns = append(columns, vs)
 			} else {
-				columns = append(columns, navalue)
+				if v, ok := data[kk]; ok {
+					vs, err := obiutils.InterfaceToString(v)
+					if err != nil {
+						log.Panicf("value %v in sequence %s for attribute %s cannot be casted to a string", v, k, kk)
+					}
+					columns[i] = vs
+				} else {
+					columns[i] = navalue
+				}
 			}
-
 		}
 		csvwriter.Write(columns)
 	}
@@ -187,8 +311,8 @@ func CLIWriteThreeColumnsToStdout(matrix *MatrixData) {
 	csvwriter := csv.NewWriter(os.Stdout)
 
 	csvwriter.Write([]string{"id", sname, vname})
-	for seqid := range *matrix {
-		for attr, v := range (*matrix)[seqid] {
+	for seqid := range matrix.matrix {
+		for attr, v := range matrix.matrix[seqid] {
 			vs, err := obiutils.InterfaceToString(v)
 			if err != nil {
 				log.Panicf("value %v in sequence %s for attribute %s cannot be casted to a string", v, seqid, attr)
diff --git a/pkg/obitools/obimatrix/options.go b/pkg/obitools/obimatrix/options.go
index 5c2216e..881cb02 100644
--- a/pkg/obitools/obimatrix/options.go
+++ b/pkg/obitools/obimatrix/options.go
@@ -6,6 +6,7 @@ package obimatrix
 
 import (
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitools/obiconvert"
+	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obitools/obicsv"
 	"github.com/DavidGamba/go-getoptions"
 )
 
@@ -14,7 +15,8 @@ var __transpose__ = true
 var __mapAttribute__ = "merged_sample"
 var __valueName__ = "count"
 var __sampleName__ = "sample"
-var __NAValue__ = "0"
+var __MapNAValue__ = "0"
+var __AllowEmpty__ = false
 
 func MatrixOptionSet(options *getoptions.GetOpt) {
 	options.BoolVar(&__threeColumns__, "three-columns", false,
@@ -32,12 +34,16 @@ func MatrixOptionSet(options *getoptions.GetOpt) {
 	options.StringVar(&__sampleName__, "sample-name", __sampleName__,
 		options.Description("Name of the coulumn containing the sample names in the three column format."))
 
-	options.StringVar(&__NAValue__, "na-value", __NAValue__,
+	options.StringVar(&__MapNAValue__, "map-na-value", __MapNAValue__,
 		options.Description("Value used when the map attribute is not defined for a sequence."))
+
+	options.BoolVar(&__AllowEmpty__, "allow-empty", __AllowEmpty__,
+		options.Description("Allow sequences with empty map"))
 }
 
 func OptionSet(options *getoptions.GetOpt) {
 	MatrixOptionSet(options)
+	obicsv.CSVOptionSet(options)
 	obiconvert.InputOptionSet(options)
 }
 
@@ -57,8 +63,8 @@ func CLISampleName() string {
 	return __sampleName__
 }
 
-func CLINaValue() string {
-	return __NAValue__
+func CLIMapNaValue() string {
+	return __MapNAValue__
 }
 
 func CLIMapAttribute() string {
@@ -68,3 +74,7 @@ func CLIMapAttribute() string {
 func CLITranspose() bool {
 	return __transpose__
 }
+
+func CLIStrict() bool {
+	return !__AllowEmpty__
+}