Javascript function and array problem

Question

I am trying to pass some data to a function that uses those arguments as identifiers for a multi dimensional array, and then return the value hardcoded to that array. I am not sure what I am doing wrong, but something is breaking.

I can get an alert() to pop before I assign any array values, but it seems to die at that point. Any help is appreciated.

    // Get Column A's number
var a1 =  Number($('#p-a').attr("numb"));

// Get Column B's number
var b1 =  Number($('#p-b').attr("numb"));

// Get status for column A
var a_status = $('#p-a').attr("status");

// Get status for column A
var b_status = $('#p-b').attr("status");

// If same, status="s" else, status="i"
var status = "";
if(a_status == b_status) { status = "s"; }else{ status = "o"; }

// Get the value of the numbers + status
var a = this_function(a1, b1, status, "2");

// Update the status div
$('#status').html(a);

function this_function(a1, a2, s, p)
{
    this_array = array();
    this_array['1']['1']['1']['1'] = "10";
    this_array['1']['1']['1']['2'] = "20";
    this_array['1']['2']['1']['1'] = "40";
    this_array['1']['2']['1']['2'] = "60";
    // 
    return this_array[a1][a2][s][p];
}

what does array return? also, this does not look much like an array to me, as it is using letter o as an index instead of 0 — glebm
– glebm, Commented Jan 19, 2011 at 23:14
and for the array, those 'o's were replaced with 1/0, editing the post to reflect this. — David Houde
– David Houde, Commented Jan 19, 2011 at 23:17
@David: "and for the array, those 'o's were replaced with 1/0, editing the post to reflect this." Except now, you have '1' and '2', no '0' in sight... — T.J. Crowder
– T.J. Crowder, Commented Jan 19, 2011 at 23:29
@David: status is still either s or o. You would get an error in any case. — Felix Kling
– Felix Kling, Commented Jan 19, 2011 at 23:35

Felix Kling · Accepted Answer · 2011-01-19 23:40:04Z

5

You cannot initialize arrays like that. Every level needs to be initialized individually. And as you don't have numerical keys only, I'd use an object instead:

var this_array = {
    '1': {
        '1': {
            'o': {
              '1': "10",
              '2': "20"
            }
        },
        '2': {
            'o': {
              '1': "40",
              '2': "60"
            }
        }
    }
};

You'd also have to define what happens if a key does not exist. E.g. currently, if status is 's' then you will get an error.

The if statement can be written shorter using the conditional operator:

var status = (a_status == b_status) ? 's' : 'o';

Update: If you really want to have a numerical array, provided the keys are numerical only, you can create the array like so:

var this_array = [
    [],                        // this_array[0]
    [                          // this_array[1]
        [],                    // this_array[1][0]
        [                      // this_array[1][1]
            [],                // this_array[1][1][0]
            [null, 10, 20]     // this_array[1][1][1][...]
        ],
        [                      // this_array[1][2]
            [],                // this_array[1][2][0]
            [null, 40, 60]     // this_array[1][2][1][...]                 
        ]
    ]
];

You see, if you do not start your indices with 0 the structure becomes quite confusing.

edited Jan 19, 2011 at 23:40

answered Jan 19, 2011 at 23:15

Felix Kling

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1 Comment

David Houde Over a year ago

Not sure why I did not comment, but this worked perfectly. Thanks for the help.

T.J. Crowder · Accepted Answer · 2011-01-19 23:17:28Z

Your array notation within this_function is incorrect (barring your having an array function that creates the array in the form you show). Notes:

function this_function(a1, a2, s, p)
{
    this_array = array(); // <== There is no `array` function in std. JavaScript
    this_array['1']['1']['o']['1'] = "10"; // <== Unless you've created an object/array at this_array['1'] (which you haven't), this line will fail
    this_array['1']['1']['o']['2'] = "20";
    this_array['1']['2']['o']['1'] = "40";
    this_array['1']['2']['o']['2'] = "60";
    // 
    return this_array[a1][a2][s][p];
}

I'm not entirely sure what this_function should do, or I'd offer a replacement function. Some thoughts:

Creating an array, you use [] (or new Array(), but that's just a longer form of the same thing).
You have to create each object/array in an array. So you can't assign to this_array['1']['1']['o']['1'], for instance, until you've created an object/array at this_array, this_array['1'], this_array['1']['1'], and this_array['1']['1']['o'].
Your this_function function will create a new array each time it's called. That seems dramatically inefficient.
JavaScript arrays aren't really arrays, they're just objects with some special features. You may just want objects, given that not all of your keys are numeric. If you really want arrays, though, they mostly start with index 0 rather than 1.
You're quite correct that array indexes are really strings, but they're almost always written as numbers and it's totally fine to do that (leaving off the quotes). Using the quotes (which is, again, technically correct) will tend to confuse people trying to maintain the code. (But if you use objects rather than arrays, it will mostly help.)

gblazex · Accepted Answer · 2011-01-19 23:31:34Z

First and foremost there is no array() function in Javascript. I don't know if it refers to some other point of your code but arrays are created via the array constructor new Array() or an array literal []

Secondly what you are using is not a real numberical indexed array.

For the assignment part: you have one array/object but the deeply nested objects/arrays are undefined.

Your code dies at: this_array['1']['1']['o']['1'] = "10"; because this_array['1'] is undefined which can't have any property so the chain is broken.

Then there is a problem with types. You convert the attribute to number by Number($('#p-a').attr("numb")); and then you use strings as indexes. This is related to the array/object confusion.

What you need is to create a real array, and use numerical indexes:

// move it outside so you only 
// create this beast once
var array = [  // first  level
  [            // second level
    [          // third  level
      [10, 20] // fourth level
    ],
    [ 
      [40, 60]
    ] 
    // , [...]
  ]
];

function this_function(a1, a2, s, p) {
    return array[a1-1][a2-1][s-1][p-1];
}

hellatan · Accepted Answer · 2011-01-19 23:18:18Z

0

i'm not well versed in needing to deal with multidimensional arrays, but you need to define all your inner arrays before you can set them to anything. something like this:

var this_array = [];
this_array['1'] = [];
this_array['1']['1'] = [];
this_array['1']['2'] = [];
this_array['1']['1']['o'] = [];
this_array['1']['2']['o'] = [];

this_array['1']['1']['o']['1'] = "10";
this_array['1']['1']['o']['2'] = "20";
this_array['1']['2']['o']['1'] = "40";
this_array['1']['2']['o']['2'] = "60";

i tried to console this result out and everything came up as undefined, but within the array at least and didn't die.

answered Jan 19, 2011 at 23:18

hellatan

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2 Comments

Felix Kling Over a year ago

I'd not use arrays like objects. this_array['1']['1']['o'] = []; will give you trouble at some point.

hellatan Over a year ago

ya, posted this before i saw your answer above, which i think is a better alternative for javascript and therefore upvoted heh

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