<?php

$arr = array(
    (object)array('pagerank' => 1),
    (object)array('pagerank' => 'R'),
    (object)array('pagerank' => 2),
);

$tmp_arr = $arr;

asort($tmp_arr);

reset($tmp_arr);

$key = key($tmp_arr);

$item = $tmp_arr[$key];

unset($arr[$key]);

$arr[$key] = $item;

var_dump($arr);

array(3) {
  [0]=>
  object(stdClass)#1 (1) {
    ["pagerank"]=>
    int(1)
  }
  [2]=>
  object(stdClass)#3 (1) {
    ["pagerank"]=>
    int(2)
  }
  [1]=>
  object(stdClass)#2 (1) {
    ["pagerank"]=>
    string(1) "R"
  }
}