﻿ PHP Array Exercise: Sort the following array by the day and username - w3resource

# 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:

PHP Code Editor:

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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