Re-key Your PHP Array with array_reduce

How much PHP code is dedicated to looping through an array of arrays (rows), comparing a search value against each row’s “column” of that name? Tons. What about re-indexing the array using the search column, so we can directly access the rows by search value?

Here’s a reducing function:

function keyBy ($reduced, $row) {
    $keyname = $reduced ['key'];
    $reduced ['data'] [$row [$keyname]] = $row;
    return $reduced;
}

The most important thing to keep in mind is the desire to obtain one value accumulated from an array. Inside keyBy, $reduced holds that value. The reduction works by accepting the currently reduced value and returning it with any updates you want. keyBy is extremely powerful because it will let me re-index an array of arrays using any column. Since an initial value for $reduced is required, I decided to make use of that argument to pass an arbitrary key name. To prevent any clashes with the data keys, I separated ‘key’ from ‘data’ in $reduced.

To “reduce” an array of rows into a direct-access array, I call keyBy by passing it to array_reduce, with the initial argument indicating which key to index by.

$customers = array (
	array ('id'    => 121, 'first' => 'Jane',	'last'  => 'Refrain'),
	array ('id'    => 290, 'first' => 'Bill',	'last'  => 'Swizzle'),
	array ('id'    => 001, 'first' => 'Fred',	'last'  => 'Founder')
);

$customersByLastName = array_reduce ($customers, "keyBy", array ('key' => 'last'));

print_r ($customersByLastName);
print $customersByLastName ['data']['Founder']['first'];

Array (
  [key] => last
  [data] => Array (
    [Refrain] => Array (
      [id] => 121
      [first] => Jane
      [last] => Refrain)

    [Swizzle] => Array (
      [id] => 290
      [first] => Bill
      [last] => Swizzle)

    [Founder] => Array (
      [id] => 1
      [first] => Fred
      [last] => Founder)
  )
)

Fred

Isn’t that an incredibly small amount of code that gets rid of a lot of code? If the array is searched more than once, it quickly becomes extremely efficient.

World’s Most Efficient Implementation of Discrete Timers in PHP

Well it may not be THE most efficient, but it’s pretty close. I’ve seen a lot of timer code in my time, and it always looks too elaborate for what it needs to do. After all, if I’m using timers then I’m probably very concerned about how long things take — I don’t want to add much overhead to track it. I came up with this code during an important project to allow me to record how long certain functionality was taking.

I wanted something that would be as simple and lightweight as possible. In order to maintain discrete timers that can’t interfere with each other, many timer implementations require instantiating a new instance of some class. Instead, I opted for a static array in my timer function, with the index of the array as a unique timer “name”; this serves the same purpose. With this function, I can print out how long the overall script has been running, at any time. I can create a new timer (which also starts it running), print how long since that timer’s been running and optionally keep the timer’s value or reset it each time I access its current value.

We need an empty static array to hold timers. The first step is to get the current system time. By passing true to microtime(), we get a float representing the number of seconds for the current time. When no timer name (the index in our static array) is passed in, we just need to subtract the script start time from current and return that.

If there is a timer name passed, that’s when things get creative. We have to get the time value from the last call with this timer, or null if the timer hasn’t been used before. If we’re initializing the timer, set it to the current system time and return 0.0 (to force the type) for its value. If the timer exists and we’re resetting (which is the default) it, set it to the current system time.

Finally we return the difference between now and the last call.

I should note that when using elapsed() for the script’s overall execution time, the value is returned in seconds, otherwise the return value is milliseconds (prevents having extremely small numeric values).

/**
* Return an elapsed milliseconds since the timer was last reset.
*
* If a timer "name" is not specified, then returns the elapsed time since the
* current script started execution. This script timer can not be "reset".
* THIS DEFAULT SCRIPT TIMER RETURNS IN SECONDS
*
* Always "resets" the specified timer unless you specify false for the reset
* parameter. Of course, on the first call for a particular timer, it will always
* reset to the time of the call.
*
* examples:
* elapsed(__FUNCTION__); // using __FUNCTION__ or __METHOD__ makes it easy to be unique
* ...
* ...
* echo "It took " . elapsed(__FUNCTION)/1000 . " seconds."
*
* @param string $sTname Name of the timer
* @param boolean $bReset Do you want to reset this timer to 0?
* @return float Elapsed time since timer was last reset
*/
function elapsed($sTname = null, $bReset = true) {

    static $fTimers = array(); // To hold "now" from previous call
    $fNow = microtime(true); // Get "now" in seconds as a float

    if (is_null($sTname))
        return ($fNow - $_SERVER['REQUEST_TIME']);

    $fThen = isset($fTimers[$sTname]) ? $fTimers[$sTname] : null; // Copy over the start time, so we can update to "now"

    if (is_null($fThen) || $bReset) {
        $fTimers[$sTname] = $fNow;
        if (is_null($fThen))
            return 0.0;
    }
    return 1000 * ($fNow - $fThen);
}

printf (
    "Since script started %f Create 2 new timers 'fred' %f and 'alice' %f", 
    elapsed(), elapsed('fred'), elapsed('alice'));

for ($i = 0; $i <100; $i++) {
    printf (
        "Since script started %f 'fred' gets reset %f, but 'alice' doesn't %f", 
        elapsed(), elapsed('fred'), elapsed('alice', false));
}

Since script started 0.391466 Create 2 new timers ‘fred’ 0.000000 and ‘alice’ 0.000000
Since script started 0.391521 ‘fred’ gets reset 0.041962, but ‘alice’ doesn’t 0.037909
Since script started 0.391545 ‘fred’ gets reset 0.021935, but ‘alice’ doesn’t 0.056982
Since script started 0.391563 ‘fred’ gets reset 0.019073, but ‘alice’ doesn’t 0.075102
Since script started 0.391578 ‘fred’ gets reset 0.015020, but ‘alice’ doesn’t 0.090122
Since script started 0.391594 ‘fred’ gets reset 0.015020, but ‘alice’ doesn’t 0.104904
Since script started 0.391609 ‘fred’ gets reset 0.015974, but ‘alice’ doesn’t 0.119925
Since script started 0.391624 ‘fred’ gets reset 0.015020, but ‘alice’ doesn’t 0.134945
Since script started 0.391639 ‘fred’ gets reset 0.015020, but ‘alice’ doesn’t 0.149965
Since script started 0.391654 ‘fred’ gets reset 0.015020, but ‘alice’ doesn’t 0.164986
Since script started 0.391669 ‘fred’ gets reset 0.014782, but ‘alice’ doesn’t 0.180006
Since script started 0.391684 ‘fred’ gets reset 0.015020, but ‘alice’ doesn’t 0.195980
Since script started 0.391699 ‘fred’ gets reset 0.015020, but ‘alice’ doesn’t 0.211000
…

I think it’s convenient to use a pattern like

function foobar () {
    elapsed (__METHOD__);
    // lots of code
    $timeused = elapsed (__METHOD__);
}

Populate a PHP Array in One Assignment

Imagine you are returning an array you need to populate with some values. This is typical:

    $myArray = array();
    $myArray['foo'] = $foo;
    $myArray['bar'] = $bar;

There are advantages to populating the array as a single assignment:

    $myArray = array(
        'foo' => $foo,
        'bar' => $bar
)

The separation of assignment statements from the initialization (and the initialization to an empty array might be many lines previous), allows for easier corruption of the entries in the array; code might be added later in between the original. People may add things to $myArray without documenting it. And just like Where to Declare, I’ll have to scan more code to determine the effect of making changes to $myArray. The second way shows the _entire_ value of $myArray being set at once, instead of parts of it. It presents a visual of the return structure and makes it harder for $myArray to go awry. I don’t have to look any further to see what $myArray is at that point.