javascript - 使用 Mapbox GL JS 计算出现次数(geojson 属性)

Question

我需要一种方法来计算 geojson 文件的每个特征的相同属性并获取如下数组: array=["type 1", "type 2","type 3","type 2","类型 1","类型 2","类型 1","类型 3","类型 1","类型 1",....]

我正在从文件加载大型 geojson 特征集合。

Answer 1

这并不是一个真正的mapbox-gl 问题。你的 GeoJson 只是标准的 JavaScript 对象，features 是标准数组:

const counts = new Map();

for (const feature of geojson.feature) {
  const alert = feature.properties.alert;

  if (!alert) {
    continue;
  }

  if (!counts.has(alert)) {
    counts.set(alert, 0);
  }

  const currentCount = counts.get(alert);
  counts.set(alert, currentCount + 1);
}

// counts will look like this
Map(
  "type1" -> 10,
  "type2" -> 8,
  "type3" -> ...
)

或者更简洁:

const counts = geojson.features.reduce((accumulatedCounts, feature) => {
  const alert = feature.properties.alert;

  if (!alert) return accumulatedCounts;
  if (!accumulatedCounts[alert]) accumulatedCounts[alert] = 0;

  accumulatedCounts[alert]++;

  return accumulatedCounts
}, {});