Add entries together based on key in array PHP - php

Question

As you can see I have a key called dateTime which holds dates. What I need to do is add all the entries together for each date and return the array. So I simply got one dateTime per date with all the entries of that day added together. I do not know the dateTime inputs ahead of time as I have a crawler that constantly inserts data into my database.
How would you go about doing that in the most efficient way? I imagine I would have to do a foreach loop and somehow check if the key value (dateTime) changes from the previous key value. And then create a brand new array that I return
An example of the array is as follows:
array (size=130)
0 =>
array (size=2)
'dateTime' => string '2015-09-01' (length=10)
'entries' => string '225' (length=3)
1 =>
array (size=2)
'dateTime' => string '2015-09-01' (length=10)
'entries' => string '218' (length=3)
2 =>
array (size=2)
'dateTime' => string '2015-09-01' (length=10)
'entries' => string '217' (length=3)
3 =>
array (size=2)
'dateTime' => string '2015-09-01' (length=10)
'entries' => string '225' (length=3)
4 =>
array (size=2)
'dateTime' => string '2015-09-02' (length=10)
'entries' => string '231' (length=3)
5 =>
array (size=2)
'dateTime' => string '2015-09-02' (length=10)
'entries' => string '220' (length=3)
6 =>
array (size=2)
'dateTime' => string '2015-09-03' (length=10)
'entries' => string '223' (length=3)
7 =>
array (size=2)
'dateTime' => string '2015-09-03' (length=10)
'entries' => string '237' (length=3)
8 =>
array (size=2)
'dateTime' => string '2015-09-03' (length=10)
'entries' => string '220' (length=3)
So it returns an array like this
array (size=130)
0 =>
array (size=2)
'dateTime' => string '2015-09-01' (length=10)
'entries' => string '660' (length=3)
1 =>
array (size=2)
'dateTime' => string '2015-09-02' (length=10)
'entries' => string '451' (length=3)
2 =>
array (size=2)
'dateTime' => string '2015-09-03' (length=10)
'entries' => string '680' (length=3)
Edit With the help of you guys, I ended up doing the following to get the right format.
function prepareArrayForGraphDates($array){
$results = [];
$finalResult = [];
foreach ($array as $value) {
if (!isset($results[$value['dateTime']])) {
$results[$value['dateTime']] = 0;
}
$results[$value['dateTime']] += $value['entries'];
}
$keyNames = array_keys($results);
for ($x = 0; $x < sizeof($results); $x++) {
$finalResult[$x]['dateTime'] = $keyNames[$x];
$finalResult[$x]['entries'] = $results[$keyNames[$x]];
}
return $finalResult;
}

Answer 1

Use the fact that array keys are unique...
$results = [];
foreach ($array as $value) {
if (!isset($results[$value['dateTime']])) {
$results[$value['dateTime']] = 0;
}
$results[$value['dateTime']] += $value['entries'];
}

Answer 2

You can use an array like a set or a dictionary, using the date as the key.
$data = [
[
'datetime'=>'2015-09-02',
'entries' => 220
]
// ... other entries snipped ...
];
$results = [];
foreach ($data as $date => $entry)
{
// if the date has already been recorded with an initial value, add to it
if (array_key_exists($date, $results) {
$results[$date] += $entry
} else {
// the date is new; add it to the results and set its initial value
$results[$date] = $entry;
}
}