Skip elements in an aray

[chandler]

I've got a routine that computes the mean and standard deviations from an array ($closeData). However, I'd like the routine to skip the the first 97 records. Here is my code that can process the entire array:

#Function for calculating Standard Deviation
function standard_deviation($std) 
    {
    $total;
    while(list($key,$val) = each($std))
        {
        $total += $val;
        }
    reset($std);
    $mean = $total/count($std);
        
    while(list($key,$val) = each($std))
        { 
        $sum += pow(($val-$mean),2);
        } 
    $var = sqrt($sum/(count($std)-1));
    return $var; 
    }

$stdev = standard_deviation($closeData);

#Loop through array
for ($i = 0; $i < count($closeData); ++$i)
{
$mean_Data[$i]=$closeData[$i];
$up1_Data[$i] = $closeData[$i] + $stdev;
$dn1_Data[$i] = $closeData[$i] - $stdev;
$up2_Data[$i] = $closeData[$i] + $stdev * 2;
$dn2_Data[$i] = $closeData[$i] - $stdev * 2;
}

I'm guessing I need adjust in both the function for standard_deviation adn the for... loop. I've tried manipulating count($std) in the function and $i in the for loop, but nothing as worked so far. Thanks for any help.

Chandler
I ran over my dogma with karma!

 

[jpadie]

is this what you were after?

<?
#Function for calculating Standard Deviation
function standard_deviation($std) 
    {
    $total;
	$cnt = count ($std);
    for ($i=97; $i<$cnt); $i++):
        $total += $str[$i];
    endfor;
	
    $mean = $total/$cnt;
        
	for ($i=97; $i<$cnt); $i++):
	    $sum += pow(($std[$i]-$mean),2);
    endfor;
    $var = sqrt($sum/($cnt-1));
    return $var; 
    }

$stdev = standard_deviation($closeData);

#Loop through array
$cnt = count ($closeData);
for ($i=97; $i < $cnt; $i++):
	$mean_Data[$i]=$closeData[$i];
	$up1_Data[$i] = $closeData[$i] + $stdev;
	$dn1_Data[$i] = $closeData[$i] - $stdev;
	$up2_Data[$i] = $closeData[$i] + $stdev * 2;
	$dn2_Data[$i] = $closeData[$i] - $stdev * 2;
endfor;
?>

 

[Itshim]

Another way would be to slice the array before sending it to the function. This would also mean that the function would need to accept a second parameter for the full count of the $closeData array. You can also take out the count() from the 'for loop' and set that to a variable. This will speed up processing because PHP will not have to 'get' the count of the array for each iteration. (Just something to keep in mind.)
Example:

<?php
#Function for calculating Standard Deviation
function standard_deviation($std, $count)
    {
    $total;
    while(list($key,$val) = each($std))
        {
        $total += $val;
        }
    reset($std);
    $mean = $total/$count;
        
    while(list($key,$val) = each($std))
        {
        $sum += pow(($val-$mean),2);
        }
    $var = sqrt($sum/($count-1));
    return $var;
    }

    
$workingData    = array_slice($closeData, 97);
$closeDataCount = count($closeData);
$stdev          = standard_deviation($workingData, $closeDataCount);

#Loop through array
for ($i = 0; $i < $closeDataCount; ++$i)
{
$mean_Data[$i]=$closeData[$i];
$up1_Data[$i] = $closeData[$i] + $stdev;
$dn1_Data[$i] = $closeData[$i] - $stdev;
$up2_Data[$i] = $closeData[$i] + $stdev * 2;
$dn2_Data[$i] = $closeData[$i] - $stdev * 2;
}
?>

I did not test this code