index out of range when working with slices - go

Question

I am trying to convert an old version jsonline into a new one (with a different structure).
Now the old file has the following structure
{"user": "myname", "uuid": "1242315425", "data": {"Niveau1": ["AUTRE", "RC"], "Niveau2": ["RA06"], "Niveau3": ["RA06_01"]}}
however, Niveau2 and Niveau3 are not always present and the length of the lists is not always the same.
The new file has a more complicated structure
{"user": "myname", "uuid": "1242315425","annotation":{"classifications":{"Niveau1":{"labels":[{"value":"AUTRE"}, {"value":"RC"}]}, "Niveau2": {"labels": [{"value":"RA06"}], "Niveau3": {"labels": [{"value":"RA06_01"}]}}}}
What I have done so far is (after parsing the files in appropriate structures) the following function
func convert(oldAnnots []AnnotV1) (newAnnots []AnnotV2) {
for _, element := range oldAnnots {
var newAnnot AnnotV2
newAnnot.User = element.User
newAnnot.Uuid = element.Uuid
if element.Data.Niveau1 != nil {
for i, annot1 := range element.Data.Niveau1 {
newAnnot.Annotation.Classif.Niveau1.Labels[i].Value = annot1
}
}
if element.Data.Niveau2 != nil {
for j, annot2 := range element.Data.Niveau2 {
newAnnot.Annotation.Classif.Niveau2.Labels[j].Value = annot2
}
}
if element.Data.Niveau3 != nil {
for k, annot3 := range element.Data.Niveau3 {
newAnnot.Annotation.Classif.Niveau3.Labels[k].Value = annot3
}
}
newAnnots = append(newAnnots, newAnnot)
}
return
}
However, I got the error saying the index [0] is out of range for my slice.
panic: runtime error: index out of range [0] with length 0
Definitions of the two structures are the following
type AnnotV1 struct {
Uuid string `json:"uuid"`
Data struct {
Niveau1 []string `json:"Niveau1"`
Niveau2 []string `json:"Niveau2"`
Niveau3 []string `json:"Niveau3"`
} `json:"data"`
User string `json:"user"`
}
and
type AnnotV2 struct {
Uuid string `json:"uuid"`
Annotation struct {
Classif struct {
Niveau1 struct {
Labels []struct {
Value string `json:value`
} `json:"labels"`
}
Niveau2 struct {
Labels []struct {
Value string `json:value`
} `json:"labels"`
}
Niveau3 struct {
Labels []struct {
Value string `json:value`
} `json:"labels"`
}
} `json:"classifications"`
} `json:"annotation"`
User string `json:"user"`
}

Answer 1

type Label struct {
Value string `json:"value"`
}
type AnnotV2 struct {
Uuid string `json:"uuid"`
Annotation struct {
Classif struct {
Niveau1 struct {
Labels []Label `json:"labels"`
}
Niveau2 struct {
Labels []Label `json:"labels"`
}
Niveau3 struct {
Labels []Label `json:"labels"`
}
} `json:"classifications"`
} `json:"annotation"`
User string `json:"user"`
}
pre-allocate the slice
if element.Data.Niveau2 != nil {
newAnnot.Annotation.Classif.Niveau2.Labels = make([]Label, len(element.Data.Niveau2))
for j, annot2 := range element.Data.Niveau2 {
newAnnot.Annotation.Classif.Niveau2.Labels[j].Value = annot2
}
}
or use append
if element.Data.Niveau2 != nil {
for _, annot2 := range element.Data.Niveau2 {
newAnnot.Annotation.Classif.Niveau2.Labels = append(newAnnot.Annotation.Classif.Niveau2.Labels, Label{annot2})
}
}