<?php

$shorten = array(
  0 => 10,
  1 => 14,
  2 => 15,
  3 => 20,
  4 => 21,
  5 => 24,
  6 => 25,
  7 => 28,
  8 => 30,
  9 => 45,
  10 => 60,
  11 => 90,
  12 => 120,
  13 => 150,
  14 => 180,
  15 => 210,
  16 => 240,
  17 => 270,
  18 => 365,
);

$data = array(
  0 => array(
    14 => '49.21',
    20 => '71.04',
    25 => '89.58',
    30 => '100.00',
  ),
  1 => array(
    180 => '412.00',
    150 => '347.00',
    120 => '285.00',
    90 => '224.00',
    60 => '165.00',
    30 => '100.00',
    14 => '47.00',
  ),
);

// default array as the base
$shorten = array_combine($shorten, array_fill(0, count($shorten), 'n/a'));

foreach($data as &$array) {
    // merge to get set members
    $array = array_merge($shorten, $array);
}
unset($array);

var_dump($data);

array(2) {
  [0]=>
  array(23) {
    [0]=>
    string(3) "n/a"
    [1]=>
    string(3) "n/a"
    [2]=>
    string(3) "n/a"
    [3]=>
    string(3) "n/a"
    [4]=>
    string(3) "n/a"
    [5]=>
    string(3) "n/a"
    [6]=>
    string(3) "n/a"
    [7]=>
    string(3) "n/a"
    [8]=>
    string(3) "n/a"
    [9]=>
    string(3) "n/a"
    [10]=>
    string(3) "n/a"
    [11]=>
    string(3) "n/a"
    [12]=>
    string(3) "n/a"
    [13]=>
    string(3) "n/a"
    [14]=>
    string(3) "n/a"
    [15]=>
    string(3) "n/a"
    [16]=>
    string(3) "n/a"
    [17]=>
    string(3) "n/a"
    [18]=>
    string(3) "n/a"
    [19]=>
    string(5) "49.21"
    [20]=>
    string(5) "71.04"
    [21]=>
    string(5) "89.58"
    [22]=>
    string(6) "100.00"
  }
  [1]=>
  array(26) {
    [0]=>
    string(3) "n/a"
    [1]=>
    string(3) "n/a"
    [2]=>
    string(3) "n/a"
    [3]=>
    string(3) "n/a"
    [4]=>
    string(3) "n/a"
    [5]=>
    string(3) "n/a"
    [6]=>
    string(3) "n/a"
    [7]=>
    string(3) "n/a"
    [8]=>
    string(3) "n/a"
    [9]=>
    string(3) "n/a"
    [10]=>
    string(3) "n/a"
    [11]=>
    string(3) "n/a"
    [12]=>
    string(3) "n/a"
    [13]=>
    string(3) "n/a"
    [14]=>
    string(3) "n/a"
    [15]=>
    string(3) "n/a"
    [16]=>
    string(3) "n/a"
    [17]=>
    string(3) "n/a"
    [18]=>
    string(3) "n/a"
    [19]=>
    string(6) "412.00"
    [20]=>
    string(6) "347.00"
    [21]=>
    string(6) "285.00"
    [22]=>
    string(6) "224.00"
    [23]=>
    string(6) "165.00"
    [24]=>
    string(6) "100.00"
    [25]=>
    string(5) "47.00"
  }
}