storing a dynamic array of values inside an object looped within a for statement

Question

I am looking to create a set of dynamically created arrays stored inside an object. the outcome would be something similar to this...

object.array0.length = 5, object.array1.length = 4, etc

the name of the array would be generated from within a for loop based on a numerical value declared elsewhere in the application.

Here is the code that I have...

var obj = {};
var weekNum = 4;

for(i=0; i < weekNum.length;i++) {
    obj['week'+i] = [];
    obj['week'+i].push(day);

    console.log('days stored in week0: '+obj.week0.length);
}

What seems to be happening is that obj['week'+i] doesn't realize that it is an array, and the push command doesn't seem to be enough to make it think so. So as a resulting value of obj.week0.length is always 1 with the actual value just being replaced each time as opposed to the array being incremented.

Also fyi, The parameter day in the above code would be passed in from another function representing any chosen day (Mon, Tues, etc)... However, the sequence and the amount of days passed in could differ but will never exceed 5 (m-f).

Anurag · Accepted Answer · 2010-06-24 03:40:44Z

1

Looks like a logic problem to me. You're always only inserting 1 day into the array unless day represents something else altogether.

var obj = {};
var weekNum = 4;

// var was missing :)
for(var i = 0; i < weekNum.length; i++) {
    // check if entry exists before creating new.
    obj['week'+i] = obj['week'+i] || [];
    // you're always only inserting 1 value inside the week array
    // don't you want to loop through the number of days
    // and insert a day entry for *this* week for each day. like this?
    // days is another array of, hmm.. days
    for(var j = 0; j <days.length; j++) {
        obj['week'+i].push(days[j]);
    }

    console.log('days stored in week0: '+obj.week0.length);
}

edited Jun 24, 2010 at 3:40

answered Jun 23, 2010 at 21:40

Anurag

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3 Comments

Jason Over a year ago

At first I thought this had solved my issue, but upon thinking about it further I realize that it is very close to the solution - however, a solution it is not(yet)... for all intents purposes... this for loop is contained inside of a function... 'day' represents a different value each time the function is called, but it is only 1 value at a time. I would like, each time the function is called and a new parameter for 'day' is passed through, that the array then gets incremented and updated with the new value. Thanks.

Anurag Over a year ago

@Jason - The problem then is that you are redeclaring the weekN property as an array each time you call the function and the loop runs. Without seeing more code, I am just blind shooting darts, but assuming the obj array is accessible to your function somehow, you only create a new week array if it doesn't already exist. updated answer

Jason Over a year ago

obj['week'+i] = obj['week'+i] || []; That solved my issue, I was able to move on to resolve other areas of the code and now it all works. Thanks!

jdmichal · Accepted Answer · 2010-06-23 21:22:12Z

0

It is not changing, because each time through the loop you reset the value to [], then push onto it. Try moving the obj['week'+i] = [] to outside the loop.

answered Jun 23, 2010 at 21:22

jdmichal

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2 Comments

SLaks Over a year ago

Wrong. i is the array variable.

jdmichal Over a year ago

Oh, right. Good point. It is still correct in spirit though... A new array is being created and a single element pushed each loop. Likely, it should be obj['week'] = [] outside the loop instead of obj['week' + i] = [].

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