<?php

$arra = Array
(
    0 => "keyword1",
    1 => "keyword1",
    2 => "keyword1",
    3 => "keyword1",
    4 => "keyword1",
    5 => "keyword1",
    6 => "keyword1",
    7 => "keyword1",
    8 => "keyword1",
    9 => "keyword1",
    10 => "keyword2",
    11 => "keyword2",
    12 => "keyword2",
    13 => "keyword3",
    14 => "keyword3",
    15 => "keyword3",
    16 => "keyword3",
    17 => "keyword3",
    18 => "keyword3",
    19 => "keyword4",
    20 => "keyword4",
    21 => "keyword4",
    22 => "keyword4",
    23 => "keyword4",
    24 => "keyword5"
);

$newarray = array_count_values($arra);

$output = array();
foreach($newarray as $key=>$val) {
    $output[] = array("0"=>$key, "count"=>$val);
}

echo '<pre>';print_r($output);echo '</pre>';