如何以编程方式实现方括号表示法

Question

给定以下数据集

const data = [
{
id: 1,
name: "zoro",
specie: "dog",
age: 3,
size: "big",
location: {
city: "city 1",
town: "city 1",
},
},
{
id: 2,
name: "nami",
specie: "dog",
age: 5,
size: "small",
location: {
city: "city 1",
town: "city 11",
},
},
{
id: 3,
name: "ocho",
specie: "cat",
age: 9,
size: "small",
location: {
city: "city x",
town: "city x",
},
},
];

我正试图通过对象数组的一些属性来获取它的摘要。细节是这些属性的一些值是其他对象，例如location

为了获得摘要，我做了以下

function tally(array, key) {
return array.reduce((previous, current) => {
previous[current[key]] = (previous[current[key]] || 0) + 1;
return previous;
}, {});
}

通过这种方式，我得到以下结果

const specieTally = tally(data, "specie"); // { dog: 2, cat: 1 }
const ageTally = tally(data, "age"); // { '3': 1, '5': 1, '9': 1 }
const sizeTally = tally(data, "size"); // { big: 1, small: 2 }
const locationTally = tally(data, "location.city"); // { undefined: 3 }

如您所见，locationTally的结果不正确。为了向前推进，我对这种可能的情况进行了手动验证。示例：

function tally(array, key) {
return array.reduce((previous, current) => {
if (key === "location.city") {
previous[current["location"]["city"]] = (previous[current["location"]["city"]] || 0) + 1;
} else {
previous[current[key]] = (previous[current[key]] || 0) + 1;
}
return previous;
}, {});
}

因此，输出如下：

const locationTally = tally(data, "location.city"); // { 'city 1': 2, 'city x': 1 }

这暂时解决了问题，但我想知道如何通过编程获得相同的结果

Answer 1

您可以尝试以下操作：

const data = [
{
id: 1,
name: "zoro",
specie: "dog",
age: 3,
size: "big",
location: {
city: "city 1",
town: "city 1",
},
},
{
id: 2,
name: "nami",
specie: "dog",
age: 5,
size: "small",
location: {
city: "city 1",
town: "city 11",
},
},
{
id: 3,
name: "ocho",
specie: "cat",
age: 9,
size: "small",
location: {
city: "city x",
town: "city x",
},
},
];

function tally(array, key) {
return array.reduce((previous, current) => {
if (key.indexOf('.') !== -1) {
let keys = key.split('.');
previous[getNestedValue(current, keys)] = (previous[getNestedValue(current, keys)] || 0) + 1;
} else {
previous[current[key]] = (previous[current[key]] || 0) + 1;
}
return previous;
}, {});
}

function getNestedValue(element, keys) {
let value = element;
keys.forEach(key => {
value = value[key];
})
return value;
}

const locationTally = tally(data, "location.city");
console.log(locationTally);

在这里，我们用一个点字符(如果存在(来分割键，然后使用一个函数来获得确切的嵌套值，该函数在分割的键上循环，并在每次迭代中深入，直到它到达末尾。不过，您可能需要添加适当的空检查。

Answer 2

您只需要解析密钥，使用数组减少

const data =
[{id:1,name:'zoro',specie:'dog',age:3,size:'big',location:{city:'city 1',town:'city 1'}},{id:2,name:'nami',specie:'dog',age:5,size:'small',location:{city:'city 1',town:'city 11'}},{id:3,name:'ocho',specie:'cat',age:9,size:'small',location:{city:'city x',town:'city x'}}]
, tally = 
(arr, key) => arr.reduce((acc, arrElm) => 
{
let ref = key.split('.').reduce((o,k) => o[k], arrElm)
acc[ref] = (acc[ref] || 0) + 1;
return acc;
}
, {})
, specieTally   = tally( data, 'specie'  )       // { dog: 2, cat: 1          }
, ageTally      = tally( data, 'age'       )     // { '3': 1, '5': 1, '9': 1  }
, sizeTally     = tally( data, 'size'        )   // { big: 1, small: 2        }
, locationTally = tally( data, 'location.city' ) // { 'city 1': 2, 'city x': 1 }
;
console.log ('specieTally:', specieTally, 'nageTally:', ageTally, 'nsizeTally:', sizeTally, 'nlocationTally:', locationTally  )

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