FeatureCollection.ForEach only iterates geometry

[iwpnd]

Hi :wave:

I want to load a geojson with a feature collection and iterate over the features with the ForEach message that the FeatureCollection provides.

func main() {
    file, err := ioutil.ReadFile(path)

    if err != nil {
        return err
    }
    fc, err := geojson.Parse(string(file), nil)
    if err != nil {
        return err
    }
    fc.ForEach(func(o geojson.Object) bool {
        if o.Empty() {
            return true
    }
    fmt.Println(o)
        return true
    })
}

>> {"type":"Polygon","coordinates":[[[13.107376098632812,52.37769505233968],[13.699264526367188,52.37769505233968],[13.699264526367188,52.63973017532399],[13.107376098632812,52.63973017532399],[13.107376098632812,52.37769505233968]]]}

If I run this I would expect to iterate over the an array of Feature and not Polygon.

Is this intentional and I have to rethink my approach?

[iwpnd]

I doubled checked the docs and noticed Children() that I could iterate over. A FeatureCollection is supposed to inherit Children() from a Collection, but doesn't so I'm stuck again. :/

[tidwall]

Hi Ben,

A FeatureCollection should inherit Collection, and it does include a Children and ForEach functions. Both should be effectively the same thing, except ForEach is exposed to all Object types, while Children really only indented for FeatureCollection and GeometryCollection types.

That said, I just tested this code to see what you are talking about.

https://play.golang.org/p/UW-w4T3nWvJ

package main

import (
    "fmt"

    "github.com/tidwall/geojson"
)

func main() {
    json := `{"type":"FeatureCollection","features":[
        {"type":"Feature","id":"A","geometry":{"type":"Point","coordinates":[1,2]},"properties":{}},
        {"type":"Feature","id":"B","geometry":{"type":"Point","coordinates":[3,4]},"properties":{}},
        {"type":"Feature","id":"C","geometry":{"type":"Point","coordinates":[5,6]},"properties":{}},
        {"type":"Feature","id":"D","geometry":{"type":"Point","coordinates":[7,8]},"properties":{}}
    ]}`

    f, err := geojson.Parse(json, nil)
    if err != nil {
        panic(err)
    }
    objsA := f.(*geojson.FeatureCollection).Children()
    var objsB []geojson.Object
    f.ForEach(func(geom geojson.Object) bool {
        objsB = append(objsB, geom)
        return true
    })
    for i := 0; i < len(objsA) && i < len(objsB); i++ {
        fmt.Printf("%d: %s\n%d: %s\n", i, objsA[i], i, objsB[i])
    }
}

Output

0: {"type":"Feature","geometry":{"type":"Point","coordinates":[1,2]},"id":"A","properties":{}}
0: {"type":"Point","coordinates":[1,2]}
1: {"type":"Feature","geometry":{"type":"Point","coordinates":[3,4]},"id":"B","properties":{}}
1: {"type":"Point","coordinates":[3,4]}
2: {"type":"Feature","geometry":{"type":"Point","coordinates":[5,6]},"id":"C","properties":{}}
2: {"type":"Point","coordinates":[5,6]}
3: {"type":"Feature","geometry":{"type":"Point","coordinates":[7,8]},"id":"D","properties":{}}
3: {"type":"Point","coordinates":[7,8]}

This is clearly wrong. It should output the entire Feature. 🤦‍♂️

[tidwall]

Found the issue. Just pushed a fix, see v1.3.1

[iwpnd]

Awesome, thank you! 🙏

[tidwall]

You're welcome and thanks for reporting. :)