PHP arrays: summing values with matching dates - php

Question

i'm trying to figure out how to sum certain values of a multi-dimensional array if they have similar dates.
Here's my array:
<?$myArray=array(
array(
'year' => 2011,
'month ' => 5,
'day' => 13,
'value' => 2
),
array(
'year' => 2011,
'month '=> 5,
'day' => 14,
'value' => 5
),
array(
'year' => 2011,
'month ' => 5,
'day' => 13,
'value' => 1
),
array(
'year' => 2011,
'month ' => 5,
'day' => 14,
'value' => 9
)
);?>
here's how i'd like the output to look:
<?$output=array(
array(
'year' => 2011,
'month ' => 5,
'day' => 13,
'value' => 3 //the sum of 1+2
),
array(
'year' => 2011,
'month '=> 5,
'day' => 14,
'value' => 14 //the sum of 5+9
)
);?>
Notice how the 4 sub-arrays were matched on year/month/day and then only the value was summed. I've seen other SO threads on this topic but can't find one where only the value is summed and not the year/month/day values too.
Thoughts?

Answer 1

It may be easiest to initially index your output array with a combination of the year/month/day:
Note: Your example array above has all its month keys with a trailing space. I'm just using month here with no trailing space.
// Initialize output array...
$out = array();
// Looping over each input array item
foreach ($myArray as $elem) {
// Initialize a new element in the output keyed as yyyy-mm-dd if it doesn't already exist
if (!isset($out[$elem['year'] . "-" . $elem['month '] . "-" . $elem['day']])) {
$out[$elem['year'] . "-" . $elem['month '] . "-" . $elem['day']] = array(
// Set the date keys...
'year' => $elem['year'],
'month' => $elem['month '],
'day' => $elem['day'],
// With the current value...
'value' => $elem['value']
);
}
// If it already exists, just add the current value onto it...
else {
$out[$elem['year'] . "-" . $elem['month '] . "-" . $elem['day']]['value'] += $elem['value'];
}
}
// Now your output array is keyed by date. Use array_values() to strip off those keys if it matters:
$out = array_values($out);
Outputs (before calling array_values()):
array(2) {
'2011-5-13' =>
array(4) {
'year' =>
int(2011)
'month' =>
int(5)
'day' =>
int(13)
'value' =>
int(3)
}
'2011-5-14' =>
array(4) {
'year' =>
int(2011)
'month' =>
int(5)
'day' =>
int(14)
'value' =>
int(14)
}
}
Update:
To do the same thing with single-key dates (rather than 3-parts) it is easier without the concatenation:
$myArray=array(
array(
'date' => '2011-05-13',
'value' => 2
),
array(
'date' => '2011-05-14',
'value' => 5
),
array(
'date' => '2011-05-13',
'value' => 7
),
array(
'date' => '2011-05-14',
'value' => 3
),
);
foreach ($myArray as $elem) {
// Initialize a new element in the output if it doesn't already exist
if (!isset($out[$elem['date']])) {
$out[$elem['date'] = array(
// Set the date keys...
'date' => $elem['date'],
// With the current value...
'value' => $elem['value']
);
}
else {
$out[$elem['date']]['value'] += $elem['value'];
}
}

Answer 2

Here's how I would do it. The result will be in $newArray with datetime objects as keys. If you just want it as an indexed array it should be pretty easy to do.
// Example array
$myArray = array(
array(
'date' => new DateTime('1993-08-11'),
'value' => 3
),
array(
'date' => new DateTime('1993-08-11'),
'value' => 5
)
);
$newArray = array();
foreach($myArray as $element)
{
$iterationValue = $element['value'];
$iterationDate = $element['date'];
$dateKey = $iterationDate->format('Y-m-d');
if(array_key_exists($dateKey, $newArray))
{
// If we've already added this date to the new array, add the value
$newArray[$dateKey]['value'] += $iterationValue;
}
else
{
// Otherwise create a new element with datetimeobject as key
$newArray[$dateKey]['date'] = $iterationDate;
$newArray[$dateKey]['value'] = $iterationValue;
}
}
nl2br(print_r($newArray));
Actually ended up doing the pretty much the same thing as #MichaelBerkowski solution. Still, having DateTime objects is always more flexible when you wan't to do things with the dates later in your application.
Edit: Now tested it and fixed errors