javascript - 在 javascript 中对数组使用 .map

Question

我是一名 R 程序员，认为 javascript 中的数组有点像 R 中的列表。在 R 中，当我想访问列表的元素时，我会使用 lapply() 和 do.call 将函数应用于内部元素，然后将结果放入新的数据结构中。我读到了 javascript 中的 map 函数，但在我的情况下似乎无法破解它:

data = {"type": "FeatureCollection",
    "crs": { "type": "name", "properties": { "name": "CRS" } },
    "features": [
        { "type": "Feature",
          "id": 6,
          "properties": {"species": "giraffe",
                 "result": 0,
                 "popup_text": "Some text" },
          "geometry": { "type": "Point", "coordinates": [ 1, 5] } },
        { "type": "Feature",
          "id": 7,
          "properties": { "species": "pig",
                  "result": 0,
                  "popup_text": "Some text" },
          "geometry": { "type": "Point", "coordinates": [ 2,3 ] } },
        { "type": "Feature",
          "id": 8,
          "properties": { "species": "goat",
                  "result": 0,
                  "popup_text": "Some Text" },
          "geometry": { "type": "Point", "coordinates": [ 1,6 ] } },
        { "type": "Feature",
          "id": 16,
          "properties": { "species": "giraffe",
                  "result": 0,
                  "popup_text": "Some Text" },
          "geometry": { "type": "Point", "coordinates": [ 3,4 ] } },
        { "type": "Feature",
          "id": 18,
          "properties": { "species": "pig",
               "result": 0,
               "popup_text": "Some Text" },
          "geometry": { "type": "Point", "coordinates": [ 2,7 ] } }
    ]
       }

因此，data.features是一个由5个元素组成的数组，每个元素包含4个数组:type、id、属性，几何。我想生成一个新数组，它只是 properties.result 值。它的结构如下:

newdata = [0, 0, 0, 0, 0]

到目前为止，我尝试了以下方法，但没有得到我想要的结果:

var result = data.features.map(function(i) {
    return{
    result: i.properties.result
    };
});
console.log(result)

我有什么想法可以做到这一点吗？最后我的目的是确定 result == 1 中是否有 any

Answer 1

要获得您想要的输出，您只需要

var result = data.features.map(function(i) {
    return i.properties.result;    
});

这将产生一个 [0,0,0,0,0] 数组。

要确定其中是否有任何一个为 1，您可以使用 Array.some

var areAny1 = result.some(function(x) { return x == 1; });

下面的实例

var data = {"type": "FeatureCollection",
    "crs": { "type": "name", "properties": { "name": "CRS" } },
    "features": [
        { "type": "Feature",
          "id": 6,
          "properties": {"species": "giraffe",
                 "result": 0,
                 "popup_text": "Some text" },
          "geometry": { "type": "Point", "coordinates": [ 1, 5] } },
        { "type": "Feature",
          "id": 7,
          "properties": { "species": "pig",
                  "result": 0,
                  "popup_text": "Some text" },
          "geometry": { "type": "Point", "coordinates": [ 2,3 ] } },
        { "type": "Feature",
          "id": 8,
          "properties": { "species": "goat",
                  "result": 0,
                  "popup_text": "Some Text" },
          "geometry": { "type": "Point", "coordinates": [ 1,6 ] } },
        { "type": "Feature",
          "id": 16,
          "properties": { "species": "giraffe",
                  "result": 0,
                  "popup_text": "Some Text" },
          "geometry": { "type": "Point", "coordinates": [ 3,4 ] } },
        { "type": "Feature",
          "id": 18,
          "properties": { "species": "pig",
               "result": 0,
               "popup_text": "Some Text" },
          "geometry": { "type": "Point", "coordinates": [ 2,7 ] } }
    ]
       };

var result = data.features.map(function(x){
      return x.properties.result;
});
console.log(result);

var areAny1 = result.some(function(x) { return x === 1 });
console.log(areAny1);