从JavaScript中的多维数组获取数据

Question

I have the following array:

var data = [{
  length: 900,
  fields: 3
},{
  length: 1150,
  fields: 4
},{
  length: 1700,
  fields: 5
}];

Now I would like to have a function that returns the fields depending on the given length like:

function getFields(length) {
   // return "3" if length <= 900
   // return "4" if length <= 1150
   // return "5" if length <= 1700
}

How could I achieve this?

Answer 1

As long as data is properly sorted, it is a simple for loop

 var data = [{ length: 900, fields: 3 },{ length: 1150, fields: 4 },{ length: 1700, fields: 5 }]; function getFields (value) { var i; for (i=0; i<data.length; i++) { if (value <= data[i].length) return data[i].fields; // exit since we found first match } return 0; // what ever the default is for no match } console.log(800, getFields(800)); console.log(900, getFields(900)); console.log(1000, getFields(1000)); console.log(1500, getFields(1500)); console.log(2000, getFields(2000)); 

or with modern array methods you can use find() which is like a for loop code above under the hood:

 var data = [{ length: 900, fields: 3 },{ length: 1150, fields: 4 },{ length: 1700, fields: 5 }]; function getFields (value) { var i; var match = data.find(function(item) { return value <= item.length }) return match ? match.fields : 0; } console.log(800, getFields(800)); console.log(900, getFields(900)); console.log(1000, getFields(1000)); console.log(1500, getFields(1500)); console.log(2000, getFields(2000)); 

Now if the data array is out of order, than it should be sorted.

Answer 2

you can iterate the data and match the conditon

 var data = [{ length: 900, fields: 3 },{ length: 1150, fields: 4 },{ length: 1700, fields: 5 }]; function getFields(len) { var fields = ''; $.each(data, function(key,value) { if(value.length<=len) fields = value.fields; }); return fields; } // call function alert(getFields(1700)); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 

Answer 3

You don't need jQuery for this, it can be done with eg a standard .find() call. Note that this assumes that the data is sorted by .length as in your example.

 var data = [{ length: 900, fields: 3 }, { length: 1150, fields: 4 }, { length: 1700, fields: 5 }]; var value = 950; var matching = data.find(x => value <= x.length); var fields = matching ? matching.fields : 0; console.log(fields); 

Answer 4

I'd define it like so:

function getFields(length) {
   var d = data
            .filter(d => d.length <= length)        // get the list of matching objects
            .sort((a, b) => b.length - a.length)    // sort descending so largest value is at the front of the array
            .shift();                               // get the first element from the array
    return (d !== undefined) ? d.fields : undefined;// if that element exists, return .fields, otherwise undefined
}

In action:

 var data = [{ length: 900, fields: 3 },{ length: 1150, fields: 4 },{ length: 1700, fields: 5 }]; function getFields(length) { var d = data .filter(d => d.length <= length) // get the list of matching objects .sort((a, b) => b.length - a.length) // sort descending so largest value is at the front of the array .shift(); // get the first element from the array return (d !== undefined) ? d.fields : undefined;// if that element exists, return .fields, otherwise undefined } var tests = [1700, 1150, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700]; console.log(tests.map(getFields)); 

While I don't know if this is performant enough for your current use case, but it's relatively readable and easy-to-follow (although this could be made more efficient if the data were always ordered by length , for instance). If you need something more performant, you could do something like this instead:

function getFields(length) {
    let d;
    let i = data.length - 1;

    while (i > -1 && d === undefined) {
        if (data[i].length <= length) {
            d = data[i].fields;
        }
        i -= 1;
    }

    return d;
}

In action:

 var data = [{ length: 900, fields: 3 },{ length: 1150, fields: 4 },{ length: 1700, fields: 5 }]; function getFields(length) { let d; let i = data.length - 1; while (i > -1 && d === undefined) { if (data[i].length <= length) { d = data[i].fields; } i -= 1; } return d; } var tests = [1700, 1150, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700]; console.log(tests.map(getFields));