Trying to add array keys without array values - php

Question

Ok, so I'm trying to write something which will analyze the US Presidential candidates.
I'm trying to add all of the values up on a given day - I'm part of the way through that.
Anyway, $romlinearray - I want to have two values inside, the date, and the value for a given day. I want to insert them inside the if ($romneydiff == 0) { block.
What I am having a problem with is generating an array with a key name (i.e. I want to be able to do $romlinearray["value"]) and have it pull a value, but the value isn't going to be inserted until later.
How can I create an array with a key, but without a value as of yet?
$resultromney = mysql_query("SELECT category, value, timestamp from results where name='".$chartname2."'");
if (!$resultromney) {
die('Invalid query, please contact administrator');
}
$posromney = 0;
$negromney = 0;
$dateromney = "1/1/2012";
$romray = array();
while ($twitromney = mysql_fetch_assoc($resultromney))
{
$romneytime = intval($twitromney["timestamp"]);
$romneydate = date('m/d/Y', $romneytime);
$romlinearray = array(); // THIS IS WHERE THE PROBLEM IS
$romneydiff = date_diff($dateromney, $romneytime);
$PLromney = 0;
$NLromney = 0;
$totalromney = 0;
if ($romneydiff == 0) {
switch ($twitromney["category"]) {
case "composed":
$PLromney = $PLromney + $twitromney["value"];
break;
case "elated":
$PLromney = $PLromney + $twitromney["value"];
break;
case "clearheaded":
$PLromney = $PLromney + $twitromney["value"];
break;
case "agreeable":
$PLromney = $PLromney + $twitromney["value"];
break;
case "energetic":
$PLromney = $PLromney + $twitromney["value"];
break;
case "unsure":
$NLromney = $NLromney + $twitromney["value"];
break;
case "tired":
$NLromney = $NLromney + $twitromney["value"];
break;
case "depressed":
$NLromney = $NLromney + $twitromney["value"];
break;
case "guilty":
$NLromney = $NLromney + $twitromney["value"];
break;
case "confused":
$NLromney = $NLromney + $twitromney["value"];
break;
case "anxious":
$NLromney = $NLromney + $twitromney["value"];
break;
case "hostile":
$NLromney = $NLromney + $twitromney["value"];
break;
case "confident":
$PLromney = $PLromney + $twitromney["value"];
break;
}
$totalromney = $PLromney - $NLromney;
$romlinearray["value"] = $totalromney + $romlinearray["value"];
}