Sort by php array - php

Question

I need to sort the notification array by the value 'start_date' DESC order from the getNotifications function:
$posts_id_arr = getPoststIds($conn);
foreach ($posts_id_arr as $key => $val) {
$total_arr[$key] = [
'notification' => getNotifications($val['post_id'], $user_id, $conn)
];
}
$response_array = array('data' => $total_arr, 'more things' => $more_array);
echo json_encode($response_array);
right now the order is by post id due to the foreach loop.
data {
notification:
[
{
post_id: “1",
start_date: "2016-10-10 08:00:00",
},
{
post_id: “1",
start_date: "2016-10-10 12:00:00",
}
],
notification:
[
post_id: “2",
start_date: "2016-10-10 09:00:00",
},
{
post_id: “2",
start_date: "2016-10-10 13:00:00",
}
]
}
And i need it to be 1: 08:00, 2: 09:00, 1: 12:00, 2: 13:00

Answer 1

You can use a custom function to sort the values in the array using uasort. Your date format is sortable using strcmp - a date in the past is lower than a date in the future, so you can use this in your comparator.
function sort_by_date($a, $b) {
return strcmp($a->start_date, $b->start_date);
}
$sorted_posts = uasort($total_arr->notification, 'sort_by_date');
$response_array = array('data' => $sorted_posts, 'more things' => $more_array);

Answer 2

However, you don't need to perform the sort inside the foreach.
You can try the below code. Change the variable name accordingly.
foreach ($points as $key => $val) {
$time[$key] = $val[0];
}
array_multisort($time, SORT_ASC, $points);
This is because of the way array_multisort works. It sorts multiple arrays, and when the $time array is sorted, the $points array is re-ordered according to the array indices in $time. The array_multisort should come after the foreach, though
Hope this would be helpful.

Answer 3

If you want to sort with the inner array you can better prefer for the usort() method.
usort — Sort an array by values using a user-defined comparison function
This function will sort an array by its values using a user-supplied comparison function. If the array you wish to sort needs to be sorted by some non-trivial criteria, you should use this function.
<?php
function cmp($a, $b)
{
return strcmp($a["fruit"], $b["fruit"]);
}
$fruits[0]["fruit"] = "lemons";
$fruits[1]["fruit"] = "apples";
$fruits[2]["fruit"] = "grapes";
usort($fruits, "cmp");
while (list($key, $value) = each($fruits)) {
echo "\$fruits[$key]: " . $value["fruit"] . "\n";
}
?>
When sorting a multi-dimensional array, $a and $b contain references to the first index of the array.
The above example will output:
$fruits[0]: apples
$fruits[1]: grapes
$fruits[2]: lemons
Alternative Solution:
You can try array_multisort() since it will sort the array based on the order that you need.
$arr = your array;
$sort = array();
foreach($arr as $k=>$v) {
$sort['field'][$k] = $v['field'];
}
array_multisort($sort['field'], SORT_DESC, $arr);
echo "<pre>";
print_r($arr);

Answer 4

You can follow these steps:
1) Define a temporary array to store the dates:
foreach ($total_arr['notification'] as $vals) {
$temp_dates[] = $vals['start_date'];
}
2) Sort the newly created temp array using arsort():
arsort($temp_dates);
3) Use array_filter() and loop to find corresponding post ids and store to resulting array:
$i = 0;
foreach ($total_arr['notification'] as $vals) {
$res['notification'][] = array_filter($vals, function($val) {
return $val['start_date'] == $temp_dates[$i];
});
$i++;
}
$response_array = array('data' => $res, 'more things' => $more_array);
Note: Not sure if it works with duplicate start_dates.

Answer 5

As iblamefish mentioned, using uasort() is the way to go - it is simple an both memory and processing efficient, compared to all the other answers. But while strcmp() does produce good results for the SQL-style dates that you have, it is not the "correct" way to handle time fields - you should parse the times and compare them as time values:
$a = [
[ "name" => "foo", "date" => "2016-08-09 10:30:00" ],
[ "name" => "bar", "date" => "2016-01-09 02:00:00" ],
[ "name" => "baz", "date" => "2016-11-02 18:21:34" ]
];
uasort($a, function($a,$b) {
return (new DateTime($a->date))->getTimestamp() - (new DateTime($b->date))->getTimestamp();
});
var_dump($a);
produces:
array(3) {
[0] =>
array(2) {
'name' =>
string(3) "foo"
'date' =>
string(19) "2016-08-09 10:30:00"
}
[1] =>
array(2) {
'name' =>
string(3) "bar"
'date' =>
string(19) "2016-01-09 02:00:00"
}
[2] =>
array(2) {
'name' =>
string(3) "baz"
'date' =>
string(19) "2016-11-02 18:21:34"
}
}
Also, closures (anonymous functions) are more fun than using old-style "text callables").