How to get cyclical values on every foreach loop iteration - php

sorry for the title but I don't know how to explain it well in few words.
I'm dealing with a php loop where I need to get particular css classes names and other stuff (such as different svg elements) at each group of 4 iteration.
This is what I need to obtain:
iteration 1 = class 1
iteration 2 = class 2
iteration 3 = class 3
iteration 4 = class 4
iteration 5 = class 1
iteration 6 = class 2
iteration 7 = class 3
(etc...)
Actually I'd like to post my attempt to get this, but this time I do not know where to begin (but probably I'm getting lost in a glass of water). Any suggestion or hints are more than welcome...

You can use the Modulo (%) operator:
for ($i = 0; $i < 40; $i++) {
$id = ($i % 4) + 1;
$classname = "class{$id}";
echo "$classname\n";
}
When you have an array of (class) names you want to use, then:
$classnames = ["class 1", "class 2", "class 3", "class 4"];
$n = count($classnames);
for ($i = 0; $i < 40; $i++) {
$index = $i % $n;
$classname = $classnames[$index];
echo "$classname\n";
}

In a foreach loop it would be: the array index % 4 + 1, to get the repeating integer sequence 1,2,3,4.
But, if you have an array of classNames in the order you want them repeated you can do something like this:
$classNames = ['won','too','tree','fower'];
$array = [1,2,3,4,5,6,7,8,9];
foreach( $array as $index => $value ){
$cssClass = $classNames[$index % count($classNames)];
echo $cssClass.",";
}
Output for the above:
won,too,tree,fower,won,too,tree,fower,won,
Anytime you whish to change that sequence you simply have to edit the $classNames array, nothing more.

Related

Optimisation of O(n4) complexity to O(n) in PHP nested for loop

I am writing one logic to iterate numbers first and then additional logic to putting them into particular subset of array.
What does this code do :
Code accept first $n
its create array of $n number from 1 to $n
Then started converting to subset of $main_array to possible one like
['1'] [1,2] [1,2,3] [2] [2,3] [3] etc. same like this
After creating subset i am counting those some subset which satisfy condition
Condition is xyz[0] should not come in subset with abc[0] vice versa xyz[i] should not come in subset abc[i]. Example 2 and 3 is coming subset then dont count that subset, same 1 and 4 is coming then dont count
here is my nested for loop :
$n = 1299;
$main_array = range(1,$n);
$counter = 0;
$count = sizeof($abc); // $abc and $xyz size will same always.
$abc = [2,1];
$xyz = [3,4];
for ($i=0; $i <$n; $i++) {
for($j = $i;$j < $n; $j++){
$interval_array = array();
for ($k = $i; $k <= $j; $k++){
array_push($interval_array,$main_array[$k]);
}
$counter++;
for ($l=0; $l < $count ; $l++) {
//if block here to additional condition using in_array() php function. which do $counter--
if(in_array($abc[$l], $interval_array) &&
in_array($xyz[$l], $interval_array)){
$counter--;
break;
}
}
}
}
$main_array i have to create on the spot after receiving $n values.
Following is cases :
when running $n = 4 its run in 4s
when running $n = 1200 or 1299 or more than 1000 its run in 60s-123s
Expected execution timing is 9s. I reduce from 124s to 65s by removing function calling inside for loop but its not coming to point.
Expectation of code is if i have array like
$array = [1,2,3];
then
subset need to generate :
[1],[1,2],[1,2,3],[2],[2,3],[3]
Any help in this ?
It's difficult to test performance against your experience, but this solution removes one of the loops.
The way you repeatedly build $interval_array is not needed, what this code does is to just add the new value from the main array on each $j loop. This array is then reset only in the outer loop and so it just keeps the last values and adds 1 extra value each time...
for ($i=0; $i <$n; $i++) {
$interval_array = array();
for($j = $i;$j < $n; $j++){
array_push($interval_array,$main_array[$j]);
// Check output
echo implode(",", $interval_array)."\n";
$counter++;
for ($l=0; $l < $count ; $l++) {
if(in_array($abc[$l], $interval_array) &&
in_array($xyz[$l], $interval_array)){
$counter--;
break 2;
}
}
}
}
adding "\n" to better understanding for subset flow.
import datetime
N = list(range(1, int(input("N:")) + 1))
affected_list = list(map(int, input("affected_list").split()))
poisoned_list = list(map(int, input("poisoned_list").split()))
start_time = datetime.datetime.now()
exclude_list = list(map(list, list(zip(affected_list, poisoned_list))))
final_list = []
for i in range(0, len(N)):
for j in range(i + 1, len(N) + 1):
if N[i:j] not in exclude_list:
final_list.append(N[i:j])
print(final_list)
end_time = datetime.datetime.now()
print("Total Time: ", (end_time - start_time).seconds)

Getting nth-child with an offset in PHP with modulus

When iterating through a loop, I've used the modulus operator in an if statement to obtain nth results pretty easily like this:
// Get 5th item in series
if ($variable->array_item % 5 == 0) {
echo $variable->array_item;
}
How do you do get the 5th item in a series with an offset of 3 (ie, 3,8,13,18,23,etc.)?
I've seen a couple of methods but I'm looking for a canonical answer and I really don't see one on S.O. right now.
Your code specifically requests numbers that are evenly divisible by 5, whereas what you want are numbers 3, 8, 13, 18, 23, etc. This is easy enough to do using almost identical code to what you have:
// set up some test data
$testArray = [];
for ($i = 1; $i <= 30; ++$i) {
$testArray[$i] = "Testing {$i}";
}
// here's where the actual work happens
foreach ($testArray as $key => $value) {
if ($key % 5 == 3) { // <-- note 3, not 0
echo "Found $value\n";
}
}
$iterator = 0;
$step = 3;
while($iterator < count($collection))
{
echo $collection[$iterator]
$iterator += $step
}

Even distribution of PHP arrays across columns

So, I want to distribute evenly lists across 3 columns. The lists cannot be broken up or reordered.
At the moment, I have 5 lists each containing respectively 4, 4, 6, 3 and 3 items.
My initial approach was:
$lists = [4,4,6,3,3];
$columns = 3;
$total_links = 20;
$items_per_column = ceil($total_links/$columns);
$current_column = 1;
$counter = 0;
$lists_by_column = [];
foreach ($lists as $total_items) {
$counter += $total_items;
$lists_by_column[$current_column][] = $total_items;
if ($counter > $current_column*$links_per_column) {
$current_column++;
}
}
Results in:
[
[4],
[4,6],
[3,3]
]
But, I want it to look like this:
[
[4,4],
[6],
[3,3]
]
I want to always have the least possible variation in length between the columns.
Other examples of expected results:
[6,4,4,6] => [[6], [4,4], [6]]
[4,4,4,4,6] => [[4,4], [4,4], [6]]
[10,4,4,3,5] => [[10], [4,4], [3,5]]
[2,2,4,6,4,3,3,3] => [[2,2,4], [6,4], [3,3,3]]
Roughly what you need to do is loop over the number of columns within your foreach(). That will distribute them for you.
$numrows = ceil(count($lists) / $columns);
$thisrow = 1;
foreach ($lists as $total_items) {
if($thisrow < $numrows){
for($i = 1; $i <= $columns; $i++){
$lists_by_column[$i][] = $total_items;
}
}else{
//this is the last row
//find out how many columns need to fit.
//1 column is easy, it goes in the first column
//2 columns is when you'll need to skip the middle one
//3 columns is easy because it's full
}
$thisrow++;
}
This will be an even distribution, from left to right. But you actually want a modified even distribution that will look symmetrical to the eye. So within the foreach loop, you'll need to keep track of 1.) if you're on the last row of three, and 2.) if there are 2 remainders, to have it skip col2 and push to col3 instead. You'll need to set that up to be able to play around with it,...but you're just a couple of logic gates away from the land of milk and honey.
So, I ended up using this code:
$lists = [4,4,6,3,3];
$columns = 3;
$total_links = 20;
$items_per_column = ceil($total_links/$columns);
$current_column = 1;
$lists_by_column = [];
for ($i = 0; $i < count($lists); $i++) {
$total = $lists[$i];
$lists_by_column[$current_column][] = $lists[$i];
//Loop until reaching the end of the column
while ($total < $items_per_column && $i+1 < count($lists)) {
if ($total + $lists[$i+1] > $items_per_column) {
break;
}
$i++;
$total += $lists[$i];
$lists_by_column[$current_column][] = $lists[$i];
}
//When exiting the loop the last time we need another break
if (!isset($lists[$i+1])) {break;}
//If the last item goes onto the next column
if (abs($total - $items_per_column) < abs($total + $lists[$i+1] - $items_per_column)) {
$current_column++;
//If the last item goes onto the current column
} else if ($total + $lists[$i+1] > $items_per_column) {
$i++;
$lists_by_column[$current_column][] = $lists[$i];
$current_column++;
}
}

How to increment number after letter in PHP

I'm looking to increment a number after a certain letter.
I have a list of own Ids and i would like to increment it without write it manually each time i add a new id.
$ids = array('303.L1', '303.L2', '303.L3', '303.L4');
so i use the END() function to extract the last id from this array.
this is what i've tried but i cannot get a result.
$i = 0;
while($i <= count($ids)){
$i++;
$new_increment_id = 1;
$final_increment = end($last_id) + $new_increment_id;
}
echo $final_increment;
New method, but it is adding me double dot between number and letter.
$i = 0;
while($i <= count($ids)){
$i++;
$chars = preg_split("/[0-9]+/", end($ids));
$nums = preg_split("/[a-zA-Z]+/", end($ids));
$increment = $nums[1] + 1;
$final_increment = $nums[0].$chars[1].$increment;
}
//i will use this id to be inserted to database as id:
echo $final_increment;
Is there another way to increment the last number after L ?
Any help is appreciated.
If you don't want a predefined list, but you want a defined number of ids returned in an $ids variable u can use the following code
<?php
$i = 0;
$number_of_ids = 4;
$id_prefix = "303.L";
$ids = array();
while($i < $number_of_ids){
$ids[] = $id_prefix . (++$i); // adds prefix and number to array ids.
}
var_dump($ids);
// will output '303.L1', '303.L2', '303.L3', '303.L4'
?>
I'm a bit confused because you say "without write it manually". But I think I have a solution:
$ids = array('303.L1', '303.L2', '303.L3', '303.L4');
$i = 0;
while($i <= count($ids)){
++$i;
//Adding a new item to that array
$ids[] = "303.L" . $i;
}
This would increment just that LAST number, starting at zero. If you wanted to continue where you left off, that'd be simple too. Just take $i = 0; and replace with:
//Grab last item in array
$current_index = $ids[count($ids) - 1];
//Separates the string (i.e. '303.L1') into an array of ['303', '1']
$exploded_id = explode('.L', $current_index);
//Then we just grab the second item in the array (index 1)
$i = $exploded_id[1];

PHP array - start at beginning if over [duplicate]

This question already has answers here:
PHP - Sequence through array and repeat [modulo-operator]
(3 answers)
Closed 9 days ago.
I have an array with 3 entries like that:
0 => "Banana",
1 => "Apple",
2 => "Strawberry"
Now, when using a for-loop like:
for($i = 1; $i < $foo; $i++) {
$myarray[$i] = $fruitarray[$i];
}
And $i gets higher than 2, we run out of this $fruitarray. So what I want to do now is always to start at the beginning of the array when it's over. So that 3 outputs "Banana", 7 "Apple" etc.
What is the best practice to achieve this (especially if $fruitarray contains many entries)?
This is generally accomplished using the modulo operator.
for($i = 1; $i < $foo; $i++) {
$myarray[$i] = $fruitarray[$i % count($fruitarray)];
}
http://php.net/manual/en/language.operators.arithmetic.php
for($i = 1; $i < $foo; $i++) {
$myarray[$i] = $fruitarray[$i%3];
}
Notice the $i%3, this is pronounced "i mod 3" and it means divide i by 3, and return the leftovers. So, 4%3=1, 7%3=1, 11%3=2, etc.
Just make sure $foo is more than 3, and this should wrap around. If $fruitarray is arbitrarily bigger than 3 items, use
$i%count($fruitarray)
One possible solution would be to check for when $i is equal to $foo - 1 and reset it to 1:
for($i = 1; $i < $foo; $i++) {
$myarray[$i] = $fruitarray[$i];
if($i == ($foo - 1))
$i = 1;
}
You should to use the modulus operator (Modulus remainder of $a divided by $b)
for($i = 1; $i < $foo; $i++) {
$j=$i%count($fruitarray);
$myarray[$i] = $fruitarray[$j];
}
http://php.net/manual/en/language.operators.arithmetic.php
Doing this with eager code is essentially intractable, as it would cause an infinite loop:
$i = 0;
$numFruits = count($fruitarray);
while (true) { // infinite loop!
$myarray[$++i] = $fruitarray[$i % $numFruits];
}
But you can come up with working code if, instead of an array, you use a function to fetch the value:
function getFruitAt($index) use ($fruitarray) {
$numFruits = count($fruitarray);
$realIndex = $index % $numFruits;
return $fruitarray[$realIndex];
}
Or, if you want to get fancy, you can use a generator or define your own Iterator type.

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