Convert an array to a CSV string.

array_to_csv.php

<?php
/**
 *  Convert an array to a CSV string.
 *
 *  @param   array   $array  The array to be converted
 *  @return  string          The newly created string
 */
function array_to_csv( $array ) {
    if(count( $array ) == 0 ) {
        return null;
    }

    ob_start();

    $df = fopen( 'php://output', 'w' );
    fputcsv( $df, array_keys( reset( $array ) ) );
    foreach( $array as $row ) {
        fputcsv( $df, $row );
    }
    fclose( $df );

    return ob_get_clean();
}