Can an array of numbers be transformed into an array of functions?

Question

Newbie asking for help: I have an array of numbers that needs to be transformed to an array of functions that return the original numbers, so instead of calling a[3], I need to call call a[3]()

E.g.:

[1,2,3] -> [
    function () {return 1;}, 
    function () {return 2;}, 
    function () {return 3;}
]

How can I go about doing this?

Why in the world do you need to do this? If you explain the real problem you're trying to solve rather than this particular solution, then we'll probably be able to help you find a much better way to attack the problem. What you are asking for seems incredibly inefficient. Create a unique function for every value in an array is wasteful and I'm 100% sure there is a better way to solve your real problem if you can tell us what you're really trying to do. — jfriend00
– jfriend00, Commented May 16, 2012 at 1:29
The answers below all result in inefficient code - that was the point of my previous paragraph. It's simply dumb to create N function closures all to return values from an array. If you explained the real problem, you could probably create one function and no closures that would solve the problem much more efficiently. I was trying to help you find a BETTER way to solve your problem. If you don't care to learn a better or more efficient way to do things, then obviously I can't make you. — jfriend00
– jfriend00, Commented May 16, 2012 at 2:26
My question was my problem. I typed it word by word from a print out. It was just an interesting question that I couldn't work out hence why I'm here. Maybe its a trick question on its own. But thanks anyway! :) — muudless
– muudless, Commented May 16, 2012 at 2:31
If this is homework, you should add the homework tag to it. That would have also changed my response. — jfriend00
– jfriend00, Commented May 16, 2012 at 2:53
No its not homework, its a question I came across. Will keep the homework tag in mind for next time. Cheers buddy. — muudless
– muudless, Commented May 16, 2012 at 4:08

qwertymk · Accepted Answer · 2012-05-16 01:24:21Z

2

var arr = [1,2,3];

for (var i = 0; i < arr.length; i++)
    arr[i] = (function(i) { return function() { return i; } })(i);

DEMO

edited May 16, 2012 at 1:24

answered May 16, 2012 at 1:18

qwertymk

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2 Comments

Imp Over a year ago

Because before the edit, you didn't have the assignment there...? (It wasn't me who downvoted, just sayin').

Imp Over a year ago

Aaand I just realised that this doesn't actually answer the question :-p

Bergi · Accepted Answer · 2012-05-16 01:24:50Z

1

[1, 2, 3].map(function(num) {
    return function(){ return num; }
});

should do the task

answered May 16, 2012 at 1:24

Bergi

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2 Comments

Imp Over a year ago

Yeah, but not in all browsers.

RobG Over a year ago

Or use a function that doesn't need it in the first place.

Will · Accepted Answer · 2012-05-22 20:44:32Z

1

function convert( arr ) {
    for ( var i = 0; i < arr.length; i++ ) {
        arr[i] = (function( a ) { return function() { return a; }; })( arr[i] );
    }
    return arr;
}

var arr = convert( [1, 2, 3] );

edited May 22, 2012 at 20:44

answered May 16, 2012 at 1:19

Will

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3 Comments

RobG Over a year ago

@Bergi—surely you're kidding. This is precisely the kind of thing that eval and Function as a function are meant for. Sure they have a little more overhead in creating the function, but they avoid the (useless, memory consuming) closure of the accepted answer.

muudless Over a year ago

Hey there, I'm a newbie trying to work this out, so I just picked the first answer that actually worked. Are you saying your answer is better? Can you please give me a quick explanation?

Will Over a year ago

@muudless The accepted answer converts the array to functions that return the index (i.e. arr[0]() returns 0, not 1)... not the corresponding number from the previous array.

Imp · Accepted Answer · 2012-05-16 01:33:50Z

0

function transform(a) {
    var result = [];

    for (var i = 0; i < a.length; i++)
        result.push(function(value) {
            return function() {
                return value;
            }
        }(a[i]));

    return result;
}

var myArray = [1, 2, 3];
var transformed = transform(myArray);

edited May 16, 2012 at 1:33

answered May 16, 2012 at 1:26

Imp

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