skip n records

[ursvmg]

Hi all,

 

I have a requirement to read a text file with around 50k lines of data.

 

I need to prepare an output array like below.

1) First i need to start with the record 1. Get every 50th record and store it in the array. Once end of file reached and if limit not crossed 5000 the proceed to next step

2) Now i need to start with second record. Get every 50th record and store it in the array.

 

This would iterate until the output array limit reaches 5000.

 

I do not want to start from top every time, as I feel, traversing the entire file every time would compromise the performance. Is it true?

 

Or Is there any other better way to achieve it? Do we have any user-defined PHP classes to achieve this?

 

Regards,

Ursvmg

[Daniel0]

Though untested, this should do it in Θ(n):

 

$res = array();
for ($i = 0, $size = 0, $max = count($lines); $size <= 5000; ++$i) {
    for ($j = $i; $j < $max; $j += 50) {
        $res[] = $lines[$j];
        ++$size;
    }
}