Extract properties and unique values from GeoJson collection

Question

Here's a geojson object, which has array of features, each feature has a properties object.

I understand that there are many question related to map arrays and objects but I couldn't find a similar case. I tried to use lodash map and groupBy to map the properties and group the values under their key but honestly I just don't know what the combination of functions should be.

I can get the property name part by doing the following:

// since properties are the same for all features
// I extract them alone first

let properties = Object.keys(features[0].properties)

properties.map(Prentelement =>
{
    let formated = {
        // this gives me the first part
        propertyName: Prentelement,

        // I can't figure out this part to map the values uniquely under
        children: [
          {
            value: "alex"
          },
          {
            value: "cairo"
          }
        ]
    }

    return formated;
})

This is an example of the input format:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "Name": "cairo",
        "Type": "Province"
      }
    },
    {
      "type": "Feature",
      "properties": {
        "Name": "alex",
        "Type": "Province"
      }
    }
  ]
}

And what I want to do is a kind of summary on each available property and their possible values across different features. Please note that a value can be repeated across features but I want it available only once in the end result. So result would be an array like this:

[
  {
    propertyName: "Name",
    children: [
      {value: "alex"},
      {value: "cairo"}
    ]
  },
  {
    propertyName: "Type",
    children: [
      {value: "Province"}
    ]
  }
]

Would a simpler output like the following be acceptable? `{ "Name": ["alex", "cairo"], "Type": ["Province"] }` ? — user7290573, Jul 11 '19 at 16:13
@user7290573 unfortunately no, i need the format like in the example for " ant design " cascader component https://ng.ant.design/components/cascader/en — Ibrahim Mohammed, Jul 11 '19 at 16:16

Shidersz · Accepted Answer · 2019-07-11T18:07:12.930

Here you have one solution using first Array.reduce() to group the features array by the properties on an object. Note we use Sets to keep unique values only. Later, on a second step, we can Array.map() the entries of the previously generated object to get the desired structure:

let input = {
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {"Name": "cairo", "Type": "Province"}
    },
    {
      "type": "Feature",
      "properties": {"Name": "alex", "Type": "Province"}
    }
  ]
};

// Step 1, group feature values by property.

let out = input.features.reduce((acc, {properties}) =>
{
    Object.entries(properties).forEach(([key, val]) =>
    {
        acc[key] = acc[key] || new Set();
        acc[key].add(val);
    });

    return acc;
}, {});

// Show the generated object on Step 1.

console.log("Step 1 - After grouping:", out);

for (const key in out)
{
    console.log(`${key} => ${[...out[key]]}`);
}

// Step 2, map the entries of the generated object.

out = Object.entries(out).map(([k, v]) =>
    ({PropertyName: k, Children: [...v].map(x => ({Value: x}))})
);

console.log("Step 2 - After mapping:", out);

.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}

Other documentation you may need to read:

wow, thank you so much, hopefully i will be able to understand how it works step by step — Ibrahim Mohammed, Jul 11 '19 at 16:39
@IbrahimMohammed I have added a log of the intermediate structure and links to additional documentation in case you need it. Hope this helps you to understand the code in a better way. — Shidersz, Jul 11 '19 at 18:09

score 1 · Answer 2 · answered Jul 11 '19 at 17:04

Another approach (using same input data provided by @Shidersz):

     const result = input.features.reduce((acc, feature) => { 
             Object.keys(feature["properties"]).forEach(key => {
                 const index = acc.findIndex(property => {
                     return property["propertyName"] === key })

                 if (index === -1) {
                      acc.push({ propertyName: key, children: [ { value: feature["properties"][key]}] })
                 } else {
                      if (acc[index].children.findIndex(child => child.value === feature["properties"][key]) === -1) {
                        acc[index].children.push({ value: feature["properties"][key] })
                      }

                 }
             })

          return acc;

      }, []);

     console.log(JSON.stringify(result));

Extract properties and unique values from GeoJson collection

2 Answers2

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