Create new elements in an array based on existing values - php

Question

I have the following array which contains a set of periods:
Array
(
Array
(
[period_start] => 1
[period_end] => 12
)
Array
(
[period_start] => 4
[period_end] => 8
)
)
I want to split the periods that overlap other periods. For example, because the second period is overlapping the first, it should split the first period into two periods so that it looks something like this:
Array
(
Array
(
[period_start] => 1
[period_end] => 3
)
Array
(
[period_start] => 4
[period_end] => 8
)
Array
(
[period_start] => 9
[period_end] => 12
)
)
So that no two periods contain a start and end value within the range of another period. But I have no idea how best to achieve this in an efficient manner. Any help would be appreciated.
EDIT: To the comments, this post was more a plea for rubber ducking, not for getting someone else to do my work for me. I've got a solution to my problem (brace yourselves):
// Sort the collection by period_start in ascending order.
function sortByPeriod(&$collection) {
usort($collection, function ($value1, $value2) {
if (!array_key_exists('period_start', $value1) || !array_key_exists('period_start', $value2)) {
return 0;
}
if ($value1['period_start'] == $value2['period_start']) {
return 0;
}
return $value1['period_start'] < $value2['period_start'] ? -1 : 1;
});
}
$periods = array();
$products = array(
array(
'period_start' => 4,
'period_end' => 8
),
array(
'period_start' => 1,
'period_end' => 12
)
);
sortByPeriod($products);
foreach ($products as $product) {
// Store them in $periods using a key, so that if an identical period comes along on a future iteration, it doesn't get counted. The keys aren't required.
if (array_key_exists('period_start', $product) && !is_null($product['period_start'])) {
if (!array_key_exists($product['period_start'] . '-' . $product['period_end'], $periods)) {
$productStart = $product['period_start'];
$productEnd = $product['period_end'];
// Go through each period already inserted
foreach ($periods as &$period) {
$periodStart = $period['period_start'];
$periodEnd = $period['period_end'];
If the product's start overlaps the period's end
if ($productStart <= $periodEnd) {
// Set that period's end to the product's start - 1
$period['period_end'] = $productStart - 1;
// If the overlapping product is entirely within the period (e.g. period is 1-12, product is 4-8, like the example provided earlier)
if ($productEnd <= $periodEnd) {
// Add a new period, whose start is the product's end + 1 and the end is the initial period's end.
$periods[($productEnd + 1) . '-' . $periodEnd] = array(
'period_start' => $productEnd + 1,
'period_end' => $periodEnd
);
// The product's period isn't entirely within the period (e.g. period is 1-6, product is 4-8)
} else {
// Add a new period from product start to period end (e.g. following the example above, the period becomes 1-3, insert 4-6)
$periods[$productStart . '-' . $periodEnd] = array(
'period_start' => $productStart,
'period_end' => $periodEnd
);
// Set the product's start to the period's end + 1 (e.g. 7)
$productStart = $periodEnd + 1;
}
}
}
// Add the period (following the example iteration above, product start = 7, end = 8)
$periods[$productStart . '-' . $productEnd] = array(
'period_start' => $productStart,
'period_end' => $productEnd
);
}
}
// After one iteration, we have 1-3, 4-6 and 7-8
}
sortByPeriod($periods);
$periods = array_values($periods);
print_r($periods);
Which works and yields the expected output as shown above. However, as you can see, it isn't very well organised and I feel as if there would be a better way to approach this.
Thank you.

Answer 1

I realised that I was going about this in a bit of a strange way. My thinking was that if I had a period range (let's say 1-8) and another (4-12), it should split these ranges up and leave it with 1-3, 4-8, 9-12. While the output is indeed the output that I desire, getting to it by splitting it up and adding new periods to compensate for the missing ranges in between was too complicated. I was thinking of it like this (and I had it working this way):
I have three loaves of bread, each a different size. I need to split them all up so that I have several slices of the loaf, enough to equal the content of the largest loaf. Okay, let's take a piece out of this loaf, a piece out of that loaf, and put it all together.
It's all a mess. Really, the best way to go about it is to use the largest loaf and cut in the exact places that the other loaves would fit, so instead of using three loaves, i'm just using one.
I put the theory into practice (using JavaScript. I can port it to PHP). First I need a way for each period to be indistinguishable, so that if my initial periods are something along the lines of 1-3, 1-12 and 4-8, it will count the 1-3 and 4-8 as two separate periods. Luckily, all of my items are products that have a normal price and a discounted price. The discounted price takes effect during the discount period.
Next, I need to identify the largest period and note it's start and end:
var range = {};
this.products.forEach(product => {
if (!range.start) {
range.start = product.start;
}
if (!range.end) {
range.end = product.end;
}
if (product.start < range.start) {
range.start = product.start
}
if (product.end > range.end) {
range.end = product.end;
}
});
Now, for each product, I iterate from start to end by 1 each iteration, storing the product's discount price if it's period is within the current iteration, or otherwise it's normal price:
var periodCounter = [];
this.products.forEach(product => {
for (i = range.start; i <= range.end; i ++) {
if (!periodCounter[i]) {
periodCounter[i] = 0;
}
if (i >= product.start && i <= product.end) {
periodCounter[i] += product.def_amount;
} else {
periodCounter[i] += product.amount;
}
}
});
Great. Now I have an array filled with prices for all products during each single one month period. Now I need to identify the actual periods. This is really easy - iterate through the array, check to see if the current price is equal to the previous price. If it is, we're still in a period. If it isn't, we've reached the end of that period and started a new one:
var periods = [];
var periodStart = 0;
var periodEnd = 0;
for (i = range.start; i <= range.end; i ++) {
if (i == range.start) {
periodStart = i;
} else {
if (periodCounter[i] != periodCounter[i-1]) {
periodEnd = i-1;
periods.push({
start: periodStart,
end: periodEnd,
amount: periodCounter[i-1]
});
periodStart = i;
}
if (i == range.end) {
periods.push({
start: periodStart,
end: i,
amount: periodCounter[i]
});
}
}
}
If by any chance the totals of two "logical" periods equal the same price, it doesn't really matter. The end user just needs to know what the price is for these periods, they gain no information in knowing that two periods equal the same price, so in essence, you might as well just concatenate those periods into one large period, which is what would happen. If it's absolutely necessary to display the true "logical" periods, instead of storing the price in the counter, use a byte value (1, 2, 4, 8, etc).
I made a codepen for this project, using Vue.js and Bulma to display the products and the correct periods. Of course, I'm open to better ways that I might be able to go about this.