How to Select from an array of arrays

Question

I'm trying to compare json data being streamed in from websockets.

An array like this would work flawlessly:

["stream","apple","orange"]

But an array of arrays not so well:

[["stream","apple","orange"],["stream","pear","kiwi"],["stream","apple","juice"]]

Any help would be greatly appreciated. Thanks in advance!

function handler(jsonString) {

    var json = jQuery.parseJSON(jsonString);

    if (json[0] == "blah") {
       //Do something
    }

    else if (json[0] == "blah2") {
        //Do something else
    }

}

user113716 · Accepted Answer · 2011-01-23 00:26:36Z

4

First reference which inner Array you want [0] from the outer, then using the same square bracket notation, reference the item in that inner Array [0][1].

if (json[0][0] == "blah") {
   //Do something
}
else if (json[0][1] == "blah2") {
    //Do something else
}

So the following examples would produce this:

json[0][0];  // "stream"
json[0][1];  // "apple"

json[1][0];  // "stream"
json[1][1];  // "pear"

// etc...

To iterate over all the items in the Arrays, you'd need a loop inside a loop. The outer one to iterate through the Arrays stored in the outer Array, and the inner loop to iterate through the values of those inner Arrays.

Like this:

for( var i = 0, len_i = json.length; i < len_i; i++ ) {
    for( var j = 0, len_j = json[ i ].length; j < len_j; j++ ) {
        // do something with json[ i ][ j ]; (the value in the inner Array)
    }
}

or if you wanted jQuery.each()^(docs):

jQuery.each( json, function(i,val) {
    jQuery.each( val, function(j,val_j) {
        // do something with val_j (the value in the inner Array)
    });
});

I'd prefer the for loops though.

edited Jan 23, 2011 at 0:26

answered Jan 22, 2011 at 23:59

user113716

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3 Comments

DrEval Over a year ago

I'm trying to find the best way to iterate through the array of arrays and tie each in to a variable that I can use to replace data on the page. Should I use $.each for this type of function? else if (json[0][0] == "stream") { //Do something else for (var i = 0; i < json.length; i++) { var stream = json[i]; var fruit1 = stream[1]; var fruit2 = stream[2]; alert(fruit1); } }

user113716 Over a year ago

@DrEval: You'd need to do a loop inside of a loop. Yes you can use $.each, or just a simple for loop. Although I'm not certain why you would want a bunch of variables. The Array storage mechanism is designed to prevent the need for multiple variables. Is it for all the values? Or just certain ones? I'll give an example of looping in a minute.

Vadim Over a year ago

@DrEval use a for loop to iterate the array, unless you have a specific need, performance is better.

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