Remove identical values except first and last - php

Question

I have a php script creating a multidimensional array:
$res = mysql_query("SELECT `date`, `temperature` FROM `general` ORDER BY `date`", $db);
$outside_temperature_array = array();
while($row = mysql_fetch_assoc($res)) {
$date = $row['date'];
$temperature = $row['temperature'];
$temp_array = array();
array_push($temp_array, $date);
array_push($temp_array, $temperature);
array_push($outside_temperature_array, $temp_array);
unset($temp_array);
}
print_r($outside_temperature_array);
The multidimensional array looks like this. It has a unix timestamp in sequential order along with a value.
Array
(
[0] => Array
(
[0] => 1452483001
[1] => 40
)
[1] => Array
(
[0] => 1452483301
[1] => 39
)
[2] => Array
(
[0] => 1452483600
[1] => 39
)
[3] => Array
(
[0] => 1452483901
[1] => 39
)
[4] => Array
(
[0] => 1452484201
[1] => 39
)
[5] => Array
(
[0] => 1452484502
[1] => 39
)
[6] => Array
(
[0] => 1452484801
[1] => 38
)
[7] => Array
(
[0] => 1452485101
[1] => 38
)
[8] => Array
(
[0] => 1452485400
[1] => 38
)
[9] => Array
(
[0] => 1452485701
[1] => 39
)
[10] => Array
(
[0] => 1452486002
[1] => 39
)
)
I want to omit all identical values except for the first and last, only when they show up sequentially. Think of this plotted on a line graph. I basically want to remove the unnecessary values that fall between two points of identical values. So the above array would change to this:
Array
(
[0] => Array
(
[0] => 1452483001
[1] => 40
)
[1] => Array
(
[0] => 1452483301
[1] => 39
)
[2] => Array
(
[0] => 1452484502
[1] => 39
)
[3] => Array
(
[0] => 1452484801
[1] => 38
)
[4] => Array
(
[0] => 1452485400
[1] => 38
)
[5] => Array
(
[0] => 1452485701
[1] => 39
)
[6] => Array
(
[0] => 1452486002
[1] => 39
)
)

Answer 1

You need to:
Keep track of the last temperature.
When a temperature change is detected, append the held row (if applicable) and the current row to the final array.
If there was no temperature change, hold the row as the last duplicate.
After the loop, append the held row to the final array if it is set.
This should work for you.
<?php
$res = mysql_query("SELECT `date`, `temperature` FROM `general` ORDER BY `date`", $db);
$outside_temperature_array = array();
$last_temp = null;
$held_row = null;
while($row = mysql_fetch_assoc($res)) {
// If we're on a new temperature
if ($row['temperature'] !== $last_temp) {
// Append and clear the held row first
if (is_array($held_row)) {
$outside_temperature_array[] = [$held_row['date'], $held_row['temperature']];
$held_row = null;
}
// Append this row and note the temperature
$outside_temperature_array[] = array($row['date'], $row['temperature']);
$last_temp = $row['temperature'];
} else {
// Hold the row in case the next row is different
$held_row = $row;
}
}
// If the last row was not appended to the array
if (is_array($held_row)) {
// Append the held row
$outside_temperature_array[] = array($held_row['date'], $held_row['temperature']);
}
print_r($outside_temperature_array);

Answer 2

$res = mysql_query("SELECT `date`, `temperature` FROM `general` ORDER BY `date`", $db);
$outside_temperature_array = array();
$oldTemperature = null;
while($row = mysql_fetch_assoc($res)) {
if($oldTemperature == $row['temperature'] && next($row)['temperature'] == $oldTemperature )
continue;
}
$oldTemperature = $row['temperature'];
$outside_temperature_array[] = array($row['date'],$row['temperature']);
}
print_r($outside_temperature_array);
You can try passed eqvivalent element in array use continue, but this code non testing. I think maybe you can execute sql query for this. And mysql this old extensions you need use PDO or Mysqli.