Initialize Nested Associative array in Javascript

Question

I have an associative array with the following structure

[location][product] and then [count] and [date] leaf entries

I am trying to initialize it using the code below

summary = {};
if(location in summary == false && product in summary == false){
        summary[location][product] = {};
}

then then iterating over an object of sales and assigning values using

summary[location][product]["count"] = count;
summary[location][product]["date"] = countDate;

but I am getting the error below, what am I missing

Type Error: summary[location] is undefined

Did you define summary earlier by using var summary?

echochamber
– echochamber

2013-11-25 21:17:04 +00:00
Commented Nov 25, 2013 at 21:17 — echochamber
– echochamber, Commented Nov 25, 2013 at 21:17
@echochamber Yes I did that.

fanbondi
– fanbondi

2013-11-25 21:20:41 +00:00
Commented Nov 25, 2013 at 21:20 — fanbondi
– fanbondi, Commented Nov 25, 2013 at 21:20
Looks like ryguy has you covered.

echochamber
– echochamber

2013-11-25 21:23:53 +00:00
Commented Nov 25, 2013 at 21:23 — echochamber
– echochamber, Commented Nov 25, 2013 at 21:23

ryguy21 · Accepted Answer · 2013-11-25 21:26:21Z

2

You need to define each nested object as you go. So instead of

summary = {};
if(location in summary == false && product in summary == false) {
    summary[location][product] = {};
}

you need to type

summary = {}

if (!(location in summary)
    summary[location] = {}

if (!(product in summary[location]))
    summary[location][product] = {}

summary[location][product]['count'] = count
summary[location][product]['date'] = countdate

This will remove the error.

There may be a more efficient way of doing this that I am not aware of, but I'm sure this works.

edited Nov 25, 2013 at 21:26

answered Nov 25, 2013 at 21:19

ryguy21

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Comments

jonasnas · Accepted Answer · 2013-11-25 21:34:37Z

1

The problem is that your code:

summary = {};
if(location in summary == false && product in summary == false) {
    summary[location][product] = {};
}

will never set product because if location is not in summary then you wont be able to set product with:

summary[location][product]

since you can't set a product property of null (location)

And later when you try to access location property with:

summary[location][product]

the same issue happens. Location is null and you can't access its property 'product'.

P.S. if location and property is not a variable they must be in quotes like 'location' or 'product'

answered Nov 25, 2013 at 21:34

jonasnas

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Comments

Archenoth · Accepted Answer · 2013-11-25 21:55:58Z

1

The problem with your code is you cannot assign multiple levels of undefined or null object members by name simultaneously, so something like this will fail:

var obj = {};
obj.member.member = someValue; // Will fail

To solve this, you could always initialize a "skeleton" of the object using an object literal before using it. That way you can avoid having to initialize the object level by level.

summary = {"location": {"product": {}}};

edited Nov 25, 2013 at 21:55

answered Nov 25, 2013 at 21:50

Archenoth

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