将值附加到 javascript 字典

Question

I am trying to create the following data structure in javascript:

d = {"foo": [3, 77, 100], "bar": [10], "baz": [99], "biff": [10]}

My starting data structure is aa list of dictionaries:

input = [{"key": "foo", "val": 3}, {"key": "bar", "val": 10}, {"key": "foo", "val": 100}, {"key": "baz", "val": 99}, {"key": "biff", "val": 10}, {"key": "foo", "val": 77]

How can I generate my desired data structure? The following code doesn't seem to append values to the value array.

var d = {}

for (var i in input) {
    var datum = input[i];
    d[datum.key] = datum.val
}

Answer 1

for (var i = 0; i < input.length; i++) {
    var datum = input[i];
    if (!d[datum.key]) {
        d[datum.key] = [];
    }
    d[datum.key].push(datum.val);
}

FYI, you shouldn't use for (var i in input) to iterate over an array.

Answer 2

Another alternative:

 const input = [{ "key": "foo", "val": 3 }, { "key": "bar", "val": 10 }, { "key": "foo", "val": 100 }, { "key": "baz", "val": 99 }, { "key": "biff", "val": 10 }, { "key": "foo", "val": 77 }] const dict = {} input.forEach(({ key, val }) => key in dict ? dict[key].push(val) : dict[key] = [val] ) console.log(dict);

And a one-liner, with immutability

input.reduce((dict, { key, val }) => ({ ...dict, [key]: [...dict[key] || [], val] }), {})

Answer 3

Another way, with reduce .

var d = input.reduce(function (res, item) {
    var key = item.key;

    if (!res[key]) res[key] = [item.val];
    else res[key].push(item.val);

    return res;

}, {});

Answer 4

you will have more then 1 key? Well, I think you want something like convert JSON to ArrayString.

Check this Convert JSON To Array Javascript and this How to convert JSON object to JavaScript array

etc

Answer 5

Please try the following:

        var input = [{ "key": "foo", "val": 3 }, { "key": "bar", "val": 10 }, { "key": "foo", "val": 100 }, { "key": "baz", "val": 99 }, { "key": "biff", "val": 10 }, { "key": "foo", "val": 77 }];
        var d = {};

        for (var i = 0; i < input.length; i++) {
            var entry = input[i];
            if (d[entry.key] === undefined) d[entry.key] = [];
            d[entry.key].push(entry.val);
        }

        alert(JSON.stringify(d));

Answer 6

var result = {}
input.forEach(function(keyObject){
  //Make array for key if doesn't exist
  result[keyObject.key] = result[keyObject.key] ? result[keyObject.key] : [];
  //Add value to array
  result[keyObject.key].push(keyObject.val);
});
console.log(result);

Answer 7

You should be do the next:

for (var i in input){
    var datuml = input[i];    
    if(!d[datuml.key]){
        d[datuml.key]=[];
    }
    d[datuml.key].push(datuml.val);
}