<?php

$fh   = fopen('ocm-users-2017-11-17.csv', 'r+');
$data = [];
$part = 0;

function save($name, array $data)
{
    if (!file_exists($name)) {
        file_put_contents($name, '');
    }

    $fh = fopen($name, 'rw+');
    foreach ($data as $row) {
        fputcsv($fh, $row);
    }
}

$headers = [];
$i       = 0;
while ($row = fgetcsv($fh, 4000)) {
    if ($i == 0) {
        $headers = $row;
        $i++;
        $data[] = $headers;
        continue;
    }

    if (count($data) >= 50000) {
        save(sprintf('cache/chunk_part_%s.csv', $part), $data);
        $data   = [];
        $data[] = $headers;
        $part++;
    }

    $data[] = $row;
    $i++;
}
save(sprintf('cache/chunk_part_%s.csv', $part), $data);