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PHP Array Exercises : Sort a specified array by the day and username

PHP Array: Exercise-22 with Solution

Write a PHP script to sort the following array by the day (page_id) and username.

Sample Solution:

PHP Code:

<?php
$arra[0]["transaction_id"] = "2025731470"; 
$arra[1]["transaction_id"] = "2025731450"; 
$arra[2]["transaction_id"] = "1025731456"; 
$arra[3]["transaction_id"] = "1025731460"; 
$arra[0]["user_name"] = "Sana"; 
$arra[1]["user_name"] = "Illiya"; 
$arra[2]["user_name"] = "Robin"; 
$arra[3]["user_name"] = "Samantha"; 

//convert timestamp to date 
function convert_timestamp($timestamp){ 
    $limit=date("U"); 
    $limiting=$timestamp-$limit; 
    return date ("Ymd", mktime (0,0,$limiting)); 
} 
//comparison function 
function cmp ($a, $b) { 
    $l=convert_timestamp($a["transaction_id"]); 
    $k=convert_timestamp($b["transaction_id"]); 
    if($k==$l){ 
        return strcmp($a["user_name"], $b["user_name"]); 
    }else{ 
        return strcmp($k, $l); 
    } 
} 
//sort array 
usort($arra, "cmp"); 

//print sorted info 
while (list ($key, $value) = each ($arra)) { 
    echo "\$arra[$key]: "; 
    echo $value["transaction_id"]; 
    echo " user_name: "; 
    echo $value["user_name"]; 
    echo "\n"; 
} 
?>

Sample Output: 

$arra[0]: 2025731450 user_name: Illiya                      
$arra[1]: 2025731470 user_name: Sana                        
$arra[2]: 1025731456 user_name: Robin                       
$arra[3]: 1025731460 user_name: Samantha

Flowchart:

Flowchart: PHP - Sort the following array by the day and user name

PHP Code Editor:

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Previous: Write a PHP function to sort subnets.
Next: Write a PHP program to sort a multi-dimensional array set by a specific key.

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PHP: Tips of the Day

PHP: ?: operator (the 'Elvis operator') in PHP

It evaluates to the left operand if the left operand is truthy, and the right operand otherwise.

In pseudocode, 

foo = bar ?: baz;

roughly resolves to

foo = bar ? bar : baz;

or

if (bar) {
    foo = bar;
} else {
    foo = baz;
}

with the difference that bar will only be evaluated once.

You can also use this to do a "self-check" of foo as demonstrated in the code example you posted:

foo = foo ?: bar;

This will assign bar to foo if foo is null or falsey, else it will leave foo unchanged.

Some more examples:

<?php
    var_dump(5 ?: 0); // 5
    var_dump(false ?: 0); // 0
    var_dump(null ?: 'foo'); // 'foo'
    var_dump(true ?: 123); // true
    var_dump('rock' ?: 'roll'); // 'rock'
?>

By the way, it's called the Elvis operator.

Ref : https://bit.ly/2SYEI83