在 javascript 中的数组上使用 .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。我在 javascript 中读到了 map 函数，但我似乎无法破解它：

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 是一个包含 5 个元素的数组，每个元素包含 4 个数组：type、id、properties、geometry .我想生成一个只有 properties.result 值的新数组。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)

有什么办法可以做到这一点吗？最后我的目的是确定 result == 1 的 any

Answer 1

I would like to generate a new array that is just the properties.result value.

你几乎走对了路

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

In the end my purpose is to determine if any of the result == 1

你可以使用filter

var hasAny1 = data.features.filter(function(i) {
    return i.properties.result == 1;
}).length > 0;
console.log(hasAny1);

或使用some

var hasAny1 = data.features.some(function(i) {
    return i.properties.result == 1;
});
console.log(hasAny1);

Answer 2

您应该 return 您希望成为新数组元素的值：

data.features.map(function (x) { 
    return x.properties.result; 
});

Answer 3

要获得您想要的输出，您只需要

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

这将导致数组 [0,0,0,0,0]。

要确定其中是否有 1 个，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);

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