在JavaScript中的数组上使用.map

Question

I'm an R programmer and think of arrays in javascript kind of like lists in R. In R when I want to access elements of a list I would use lapply() and do.call to apply a function to the inner elements and then place the result into a new data structure. I read about the map function in javascript but I can't seems to crack it in my case:

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 ] } }
    ]
       }

So, data.features is an array of 5 elements, each of these elements contains 4 arrays: type , id , properties , geometry . I would like to generate a new array that is just the properties.result value. It would have a structure like this:

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

So far I tried the following but it doesn't result in what I want:

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

Any ideas how I can do this? In the end my purpose is to determine if any of the result == 1

Answer 1

To get the output you wanted you just needed

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

That will result in an array of [0,0,0,0,0] .

To determine if any of them are 1 you could use Array.some

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

Live example below

 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); 

Answer 2

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

You were almost on the right path

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

you can use filter

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

Or use some

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

Answer 3

You should just return the value that you want to be an element of the new array:

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