How to simplify nested loops and conditions?

Question

Given a JS as follows:

for (c in chars) {
    for (i in data) {
        if (data[i].item === chars[c]) {
            // do my stuff;
        }
        else { /* do something else */}
    }
}

and data such:

var chars = [ 'A', 'B', 'C', 'A', 'C' ];
var data = [
    {'item':'A', 'rank': '1'}, 
    {'item':'B', 'rank': '2'}, 
    {'item':'C', 'rank': '3'}
    // no duplicate
];

Is there a simpler syntax to express that rather than nested for loops and inner conditions?

I try to match two datasets, more precisely to use chars's keys to iterate data and find values.

Wait, are you trying to iterate over an array with for in? — acdcjunior
– acdcjunior, Commented Jul 20, 2013 at 22:34
@acdcjunior It works. Just remember that the iteration variable is set to the indexes, not the values (it's not like PHP foreach). — Barmar
– Barmar, Commented Jul 20, 2013 at 22:35
@Barmar What works? The for in for arrays? If so, I'm not saying it doesn't, I'm say one shouldn't, as it can screw your code up. — acdcjunior
– acdcjunior, Commented Jul 20, 2013 at 22:37
@Hugolpz: Yeah, I think your nested loops are about as simple as they can get. In this specific case, a key/value map is definitely the way to go. Will be faster too. — user2437417
– user2437417, Commented Jul 21, 2013 at 19:31

Barmar · Accepted Answer · 2013-07-20 22:38:13Z

1

You could do this:

for (i = 0; i < data.length; i++) {
    if (chars.indexOf(data[i].item) != -1) {
        // Do something
    } else {
        // Do something else
    }
}

However, if chars is large, I would create an object whose keys are the elements of chars and use if (chars_obj[data[i].item]). This is more efficient than searching an array every time.

answered Jul 20, 2013 at 22:38

Barmar

789k57 gold badges555 silver badges669 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

adeneo Over a year ago

with a sidenote: Array.indexOf isn't supported in older browsers.

user2437417 Over a year ago

I don't know what OP specifically needs, but this will be a little different if there's more than one of the same letter in the chars Array.

Christophe Over a year ago

@Barmar this is not what the OP wants. With the OP example, 15 functions are executed (either my stuff or something else).

Eliran Malka · Accepted Answer · 2013-07-21 17:49:46Z

An alternative to simplifying the code would be to encapsulate and abstract it away into a utility that accepts callbacks, than reuse that whenever needed, like so:

// definition
function eachChar(onMatch, onMismatch) {
    for (c in chars) {
        for (i in data) {
            if (data[i].item === chars[c]) {
                typeof onMatch === 'function' && onMatch(); 
            } else {
                typeof onMismatch === 'function' && onMismatch(); 
            }
        }
    }
}

// usage examples
eachChar(function() {
    // do something when it's a match
});
eachChar(function() {
    // do something when it's a match
}, function() {
    // do something else when it's not
});

See a live demo on jsFiddle.

As a sidenote, you would want to explicitly declare variables used as loop indexes, as to not exposing them in an outer scope (e.g. the global scope):

// that:
for (c in chars) {
    for (i in data) {

// would become this:
for (var c in chars) {
    for (var i in data) {

Eliran Malka · Accepted Answer · 2013-07-20 23:16:45Z

0

Since you tagged your question jquery, you could use a jquery solution:

$.each(chars, function (cndx, chr) {
    $.each(data, function (dndx, datum) {
        if (datum.item === chr) {
            // do my stuff;
        } else {
            /* do something else */
        }
    }
});

Not any more succinct, but at least you don't have to index.

edited Jul 20, 2013 at 23:16

Eliran Malka

16.4k7 gold badges80 silver badges103 bronze badges

answered Jul 20, 2013 at 22:40

Chip Camden

2201 silver badge7 bronze badges

2 Comments

Christophe Over a year ago

It's not really simpler, only camouflage.

Chip Camden Over a year ago

Not entirely true -- indexing is often a vector for subtle bugs.

Collectives™ on Stack Overflow

How to simplify nested loops and conditions?

3 Answers 3

3 Comments

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related