Sort JSON file in PHP by date

Question

My question is quite similar to others about sort, but I finally didn't find answer, so I'm posting.

After JSON encode, I have got array like this.

 array(2) 
    { [0]=> array(105)
        { [0]=> array(25) 
            { ["id"]=> int(6118) 
            ["region_id"]=> int(2) 
            ["region"]=> string(6) "Region" 
            ["offer_issuer_id"]=> int(1) 
            ["offer_issuer"]=> string(11) "Some issuer" 
            ["profession_id"]=> int(3614) 
            ["profession"]=> string(33) "some profession info" 
            ["position"]=> string(45) "Some position info" 
            ["kind"]=> string(8) "parttime" 
            ["expiration_date"]=> string(10) "2015-08-09" 
            ["url"]=> string(57) "some_url_address" 
            ["created_at"]=> string(24) "2015-07-09T09:57:05.000Z" 
            ["updated_at"]=> string(24) "2015-07-09T09:57:05.000Z"
[...] 
        } 
        [1]=> array(25) 
            { 
            ["id"]=> int(6150) 
            ["region_id"]=> int(2) 
            ["region"]=> string(6) "Region" 
            ["offer_issuer_id"]=> int(1) 
            ["offer_issuer"]=> string(11) "Some issuer" 
            ["profession_id"]=> int(3599) 
            ["profession"]=> string(23) "some profession info" 
            ["position"]=> string(38) "Some position info"
            ["kind"]=> string(8) "parttime" 
            ["expiration_date"]=> string(10) "2015-08-15" 
            ["url"]=> string(57) "some_url_address" 
            ["created_at"]=> string(24) "2015-07-18T11:49:43.000Z" 
            ["updated_at"]=> string(24) "2015-07-18T11:49:43.000Z" 
            [...] 
            } 
        [2]=> array(25) 
            { 
            ["id"]=> int(6165) 
            ["region_id"]=> int(2) 
            ["region"]=> string(6) "region" 
            ["offer_issuer_id"]=> int(1) 
            ["offer_issuer"]=> string(11) "Some issuer" 
            ["profession_id"]=> int(8443) 
            ["profession"]=> string(23) "some profession info" 
            ["position"]=> string(38) "Some position info"
            ["kind"]=> string(8) "parttime" 
            ["expiration_date"]=> string(10) "2015-08-16" 
            ["url"]=> string(57) "some_url" 
            ["created_at"]=> string(24) "2015-07-27T09:53:52.000Z" 
            ["updated_at"]=> string(24) "2015-07-27T09:53:52.000Z" 
    [...] 
            }

I have to sort this data by date, but everytime I'm trying, I get error

"Notice: Undefined index: created_at in D:\xampp... on line 53

This is some sort code:

function sortFunction ($a, $b){
    return strtotime($a["created_at"]) - strtotime($b["created_at"]);

}
usort($json, "sortFunction");

I think the problem is in return syntax - I can't get into created_at variable. Any tips how to do it?

Try return strtotime($a[0]["created_at"]) - strtotime($b[0]["created_at"]); — Narendrasingh Sisodia
– Narendrasingh Sisodia, Commented Aug 3, 2015 at 13:44

Carlos Arturo Alaniz · Accepted Answer · 2015-08-03 16:16:24Z

1

Your error is on this expression

return strtotime($a["created_at"]) - strtotime($b["created_at"]);

You are dealing with a multi-dimensional array, so you need to specify keys for every dimension.

Based on you JSON dump I can see that you have One array of 2 elements. Indices 0 to 1

Element 0 contains an array of 105 elements. Indices 0 to 104

Each of those Elements are themselves associative arrays of 25 elements each. Distinct string keys.

So In order to access the created_at value that you are looking for, you need to access each of those levels of the head array.

$a[0][0]["created_at"]; //first element
$a[0][1]["created_at"]; //second element
$a[0][2]["created_at"]; //third element
$a[0][3]["created_at"]; //fourth element
...

Will get you the value you are looking for.

answered Aug 3, 2015 at 16:16

Carlos Arturo Alaniz

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