PHP: Counting elements using for loops

Question

I would like to count numeric values in a group of two for equal values. For example for list of values 1,2,3,3,3,3,3,3,3,3,5,5,6

I should have 1,2,(3,3),(3,3),(3,3),(3,3),(5,5),6

That is when I decide to count the first (3,3) are counted as 1. Therefore in this case I should have $count=8 instead of $count=13 for all values. I have tried to do some for loops and if statements but I get wrong results. Any idea is highly appreciated. Thanks

Note: the pairs have to be adjacent to be regarded as 1.

Whilst you loop, keep track of the previous loop's number in a variable, and in the current iteration if the value is the same then do not increment the counter, and clear the tracking variable so your next iteration starts again. You should also reset the tracking variable with the current value when the previous value doesn't match. — Scuzzy
– Scuzzy, Commented Jun 4, 2012 at 6:44
Note really. If distinct values, only a maximum of 2 they should be grouped together i.e for values 3,3,3 we have (3,3),3 hence the count obtained is 1,2 instead of 1,2,3 — felix cheruiyot
– felix cheruiyot, Commented Jun 4, 2012 at 6:46

Scuzzy · Accepted Answer · 2012-06-04 06:49:34Z

4

$list = array(1,2,3,3,3,3,3,3,3,3,5,5,6);
$counter = 0;
foreach($list as $number)
{
  if(isset($previous) and $previous === $number)
  {
    unset($previous);
  }
  else
  {
    $previous = $number;
    $counter++;
  }
}
echo $counter; // 8

answered Jun 4, 2012 at 6:49

Scuzzy

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2 Comments

felix cheruiyot Over a year ago

Thanks Scuzzy.I have never use the unset() before. You have taught me something new. It works perfectly too +1 for that

Andreas Wong Over a year ago

consider accepting his answer by clicking on the V sign on the top left of his answer

Ja͢ck · Accepted Answer · 2012-06-04 23:53:57Z

3

Regular expression solution with back references:

$s = '1,2,3,3,3,3,3,3,3,3,5,5,6';

echo count(explode(',', preg_replace('/(\d+),\\1/', '\\1', $s)));

Output:

The regular expression matches a number and then uses a back reference to match the number adjacent to it. When both are matched, they are replaced by one number. The intermediate result after the preg_replace is:

1,2,3,3,3,3,5,6

After that, the count is performed on the comma separated values.

edited Jun 4, 2012 at 23:53

answered Jun 4, 2012 at 6:47

Ja͢ck

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3 Comments

Ja͢ck Over a year ago

Missed the counting requirement earlier on :)

felix cheruiyot Over a year ago

No problem. You made it easy,fewer lines of code than I expected.Thanks a bunch.It works perfect.

Ja͢ck Over a year ago

@nairobicoder great, I hope you can understand the regular expression :)

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