How can I optimize the following code ,
I Need to run 3 sets of loops like this:
for($i=1;$i<=$count-1;$i++){
for($j=$i+1;$j<=$count;$j++){
// do some query use $i and $j
}
}
for($i=1;$i<=$count-2;$i++){
for($j=$i+1;$j<=$count-1;$j++){
for($k=$j+1;$k<=$count;$k++){
// do some query use $i and $j and $k
}
}
}
for($i=1;$i<=$count-3;$i++){
for($j=$i+1;$j<=$count-2;$j++){
for($k=$j+1;$k<=$count-1;$k++){
for($l=$k+1;$l<=$count;$l++){
// do some query use $i and $j and $k and $l
}
}
}
}
Is there a way to simplify the code, perhaps to connect the loops together ?
thanks !
This should do it (untested):
for($i = 1; $i <= $count - 3; $i++) {
for($j = $i + 1; $j <= $count; $j++) {
// i,j query
if($j > $count - 2) {
continue;
}
for($k = $j + 1; $k <= $count; $k++) {
// i,j,k query
if($k > $count - 1) {
continue;
}
for($l = $k + 1; $l <= $count; $l++) {
// i,j,k,l query
}
}
}
}
Note that the queries are no longer in their original order.
As it has been said, there's no way to optimize this further without knowing the queries you are running.
The big problem is that the inner loops are run multiple times. You can get around this by checking i === 1 and j === 2 inside the loops and only running the appropriate code if true.
Micro-optimization:
Use
++$i
rather than
$i++
and equivalent for $j++, $k++ and $l++
But what are you doing in these loops: it's entirely possible that your do some query (database?) could be changed to remove the loops completely... and that would be far more effective than any micro-optimisations
Related
Why this piece of code works when it is clearly wrong in the second for loop (for ($i==0; $i<$parts; $i++) {)?
Does php allows for multiple comparisons inside for loops?
function split_integer ($num,$parts) {
$value = 0;
$i = 0;
$result = [];
$modulus = $num%$parts;
if ($modulus == 0) {
for($i = 0; $i < $parts; $i++)
{
$value = $num/$parts;
$result[] = $value;
}
} else {
$valueMod = $parts - ($num % $parts);
$value = $num/$parts;
for ($i==0; $i<$parts; $i++) {
if ($i >= $valueMod) {
$result[] = floor($value+1);
} else {
$result[] = floor($value);
}
}
}
return $result;
}
Code for ($i==0; $i < $parts; $i++) runs because $i==0 has no impact on loop.
In normal for loop first statement just sets $i or any other counter's initial value. As you already set $i to 0 earlier, your loop runs from $i = 0 until second statement $i < $parts is not true.
Going further, you can even omit first statement:
$i = 0;
for (; $i < 3; $i++) {
echo $i;
}
And loop will still run 3 times from 0 to 2.
My niece is trying to create one for-loop (php), that results in this:
* 12345678910987654321
example for loop she tried:
for ($i = 1; $i <= 10; $i++ , $i = 10; $i <= 1; $i--) {
echo $i . ' ';
}
She can only use if's and elseif's. I'm not a programmer and can't really help her. Any ideas how this could be achieved in php?
Any information would be greatly appreciated.
The key is to add a variable instead of a number, then reverse that number when $i hits 10.
for($i = 1, $j = 1; $i> 0; $i+=$j) // Start i at 1, and j at 1
{
echo $i;
if($i == 10)
$j = -1; // i has hit 10, so use -1 to start subtracting
}
Another possibility is to loop up to 20, printing $i for the ascending part and 20 - $i for the descending.
for ($i = 1; $i < 20; $i++) {
if ($i <= 10) {
echo $i;
} else {
echo 20 - $i;
}
}
for ($i=40; $i>=30; $i--) //code will display data for top x row
for ($i=1; $i<=9; $i++) //code will display data for left y column
for ($i=29; $i>=21; $i--) //code will display data for bottom x row
for ($i=30; $i>=39; $i++) //code will display data for right y column
These 4 loops all do the same thing.
In my index.php im using "include" to get the 4 loops that are in 4 different files.
How can I make the for loop dynamic?
Algoritihm:
$i = (40,1,29,30) <--will be any of those 4
$maxlow = (30,9,21,39)
$check =(>,<) <--value depends on whether $i > or < $maxlow
$icrement = (--,++) <-- if $check is > then decrease, otherwise increment
for ($i; $i($check)=$maxlow; $i($increment) <---what i am trying to do
// $step is either 1 (incrementing) or -1 (decrementing)
foreach (range($begin, $maxlow, $step) as $i) {
}
Settings for given loop:
$diff = -1;
$start = 40;
$stop = 30 + $diff;
The loop itself, always like this:
for ($i = $start; $i != $stop; $i += $diff)
$low = [40,1,29,30](rand(0,3);
$high = [30,9,21,39](rand(0,3);
$modifier = ($low > $high) ? -1 : 1;
for($i = $low; ($i * $modifier) < ($high * $modifier); $i += $modifier)
{
doStuff();
}
why not just use for with switch inside, like this:
for ($i=1; $i >=39; $i++) {
switch($i) {
case ($i>=1 && $i<=9):
break;
...
...
case ($i>40):
//do something
break;
}
}
It will be much more readable, and easier to understand/edit in future.
I'm trying to align strings in PHP using Levenshtein distance algorithm. The problem is that my back tracing code does not work properly for all cases. For example when the second array has inserted lines at the beginning. Then the back tracing will only go as far as when i=0.
How to properly implement back tracing for Levenshtein distance?
Levenshtein distance, $s and $t are arrays of strings (rows)
function match_rows($s, $t)
{
$m = count($s);
$n = count($t);
for($i = 0; $i <= $m; $i++) $d[$i][0] = $i;
for($j = 0; $j <= $n; $j++) $d[0][$j] = $j;
for($i = 1; $i <= $m; $i++)
{
for($j = 1; $j <= $n; $j++)
{
if($s[$i-1] == $t[$j-1])
{
$d[$i][$j] = $d[$i-1][$j-1];
}
else
{
$d[$i][$j] = min($d[$i-1][$j], $d[$i][$j-1], $d[$i-1][$j-1]) + 1;
}
}
}
// backtrace
$i = $m;
$j = $n;
while($i > 0 && $j > 0)
{
$min = min($d[$i-1][$j], $d[$i][$j-1], $d[$i-1][$j-1]);
switch($min)
{
// equal or substitution
case($d[$i-1][$j-1]):
if($d[$i][$j] != $d[$i-1][$j-1])
{
// substitution
$sub['i'][] = $i;
$sub['j'][] = $j;
}
$i = $i - 1;
$j = $j - 1;
break;
// insertion
case($d[$i][$j-1]):
$ins[] = $j;
$j = $j - 1;
break;
// deletion
case($d[$i-1][$j]):
$del[] = $i;
$i = $i - 1;
break;
}
}
This is not to be nit-picky, but to help you find the answers you want (and improve your implementation).
The algorithm you are using is the Wagner-Fischer algorithm, not the Levenshtein algorithm. Also, Levenshtein distance is not use to align strings. It is strictly a distance measurement.
There are two types of alignment: global and local. Global alignment is used to minimize the distance between two entire strings. Example: global align "RACE" on "REACH", you get "RxACx". The x's are gaps.
In general, this is the Needleman-Wunsch algorithm, which is very similar to the Wagner-Fischer algorithm. Local alignment finds a substring in a long string and minimizes the difference between a short string and a the substring of the long string.
Example: local align "BELL" on "UMBRELLA" and you get "BxELL" aligned on "BRELL". It is the Smith-Waterman algorithm which, again, is very similar to the Wagner-Fischer algorithm.
I hope that this is helpful in allowing you to better define the exact kind of alignment you want.
I think your bug is exactly what you say in your question that it is: you stop as soon as i==0, instead of going all the way to i==0 && j==0. Simply replace this condition:
while($i > 0 && $j > 0)
with
while ($i > 0 || $j > 0)
and you're halfway to your solution. The tricky bit is that if $i==0, then it's incorrect to use the array index $i-1 in the loop body. So you'll also have to change the body of the loop to something more like
while ($i || $j) {
$min = $d[$i][$j]; // or INT_MAX or something
if ($i && $j && $min > $d[$i-1][$j-1]) {
$newi = $i-1;
$newj = $j-1;
$min = $d[$newi][$newj];
}
if ($i && $min > $d[$i-1][$j]) {
$newi = $i-1;
$newj = $j;
$min = $d[$newi][$newj];
}
if ($j && $min > $d[$i][$j-1]) {
$newi = $i;
$newj = $j-1;
$min = $d[$newi][$newj];
}
// What sort of transformation is this?
if ($newi == $i && $newj == $j) {
assert(false); // should never happen
} else if ($newi == $i) {
// insertion
$ins[] = $j;
} else if ($newj == $j) {
// deletion
$del[] = $i;
} else if ($d[$i][$j] != $d[$newi][$newj]) {
// substitution
$sub['i'][] = $i;
$sub['j'][] = $j;
} else {
// identity
}
assert($newi >= 0); assert($newj >= 0);
$i = $newi;
$j = $newj;
}
Why does this for loop work with each condition on their own, but together the first condition doesn't matter?
for ($j = 0; $j < 5 or $j < $synCount; $j++)
I only want the loop run five times
or
if synCount is less than this.
You probably mean "$j under 5 and $j under $sysCount", or:
$j < min(5, $sysCount)
very simple
$j < min(5, $sysCount)
You can youse the break statement to leave the for loop :
for ($j = 0; $j < 5 ; $j++)
{
if( $j >= $synCount )
break;
//treatment
}
Or calculate your limit before the loop :
$ max = $synCount < 5 ? $synCount : 5;
for ($j = 0; $j < $synCount ; $j++)
{
//treatment
}
Another solution,quickest : use min() :
for ($j = 0; $j < min(5, $synCount) ; $j++)
{
//treatment
}
Try it like this:
$loopcount = ($syncount < 5) ? $syncount : 5;
for ($j = 0; $j < $loopcount; ++$j) {
}
The first line determines whether $syncount is less than 5 or not and then assigns a value to $loopcount based on that. Then the loop runs the required number of times.
for ($j = 0; $j < ($syncCount <= 5 ? $syncCount : 5); $j++)
or slightly optimized (but I guess with 5 or less iterations this absolutely doesn't matter)
for ($j = 0, $limit = min($syncCount, 5); $j < $limit; $j++)
Anothe nice solutions
foreach (range(0, min($syncCount, 5)) as $j)
Sidenote
$syncCount <= 5 ? $syncCount : 5 == min($syncCount, 5)
$productsprice=ProductPrice::model()->findAllByAttributes(array ('product_id'=>$products_data->product_id));
foreach($productsprice AS $productsprice):
for($quantity = 0; $quantity <= 10; $quantity++)
{
echo '<li >'.array(value=>'ProductPrice::model()->getquantity($data->quantity)').'</li>' ;
}
endforeach;
Two conditions may indeed be applied inside for loop using logical operator. For example check status until it's ok
for($i = 0; $i < 100 && $status != 'ok'; $i++){
sleep(1);
$status = checkStatus();
}
Otherwise you need to use additional if expression with break
for($i = 0; $i < 100; $i++){
sleep(1);
$status = checkStatus();
if($status == 'ok') break;
}