Dictionary equivalent data structure?

I'm working in JavaScript and want to keep a l开发者_Python百科ist of set km/mph approximations to hand. (I can't convert programmatically, I'm working with an external API that expects certain values, so it really does have to be a dictionary equivalent.)

Currently I'm using an object:

var KM_MPH = { 10: 16, 12: 20, 15: 24 };

Going from mph to km is pretty easy:

var km = KM_MPH[10];

How do I find mph, given km? Also, is an object the best data structure to use for this sort of thing in JavaScript? I'm more used to Python.

A basic JavaScript object is in fact the best choice here. To find a reverse mapping, you can do:

function mphToKM(val){
    for(var km in KM_MPH){
        if(KM_MPH[km] === val){
            return km;
        } 
    }

    return null;
}

Or, if you anticipate having to do a lot of lookups, I would recommend having a secondary JS Object that is the mirror of the first

var mph_km = {};
for(var km in KM_MPH){
    mph_km[KM_MPH[km]] = km;
}

// mph_km[16] ==> 10

I don't know if you are in fact doing this for conversion between kilometres per hour to miles per hour... if so, it seems to make more sense to just do the conversion directly instead of relying on a hash mapping of the values.

var conversionRate = 1.609344; // kilometres per mile
function kphToMPH(val){
    return val / conversionRate ;
}

function mphToKPH(val){
    return val * conversionRate;
}

You can use iterate over all entries to find to find your key Mostly a dict is used to from key=>value

Alternatively you can have two lists var km = []; var mph = [];

with their corresponding indices mapped

This is much closer to a Dictionary data structure, since you can have dozens of elements:

var dictionary = [
    { key: 10, value: 12 },
    { key: 12, value: 20 },
    { key: 15, value: 24 }
];

Then you can also use some JavaScript Framework like jQuery to filter elements:

var element = $.filter(dictionary, function() {
    return $(this).attr("key") == 10;
});

alert($(element).attr("value"));

Yes, the JavaScript object is the correct choice.

Create a second object to do the reverse lookup:

var i, MPH_KM = {};
for(i in KM_MPH) MPH_KM[KM_MPH[i]] = i;

var mph = MPH_KM[16];

The dictionary equivalent structure for a javascript object would look like this:

var dictionary = { keys:[], values:[] };

Above structure is an equivalent of

Dictionary(Of Type, Type) **For VB.Net**
Dictionary<Type, Type>) **For C#.Net**

Hope this helps!