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find the nearest key, value, and delta from provided array of data.
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| <?php | |
| /** | |
| * Example of usage and results | |
| * $a = [ 7, -10, 13, 8, 4, -7.2, -12, -3.7, 3.5, -9.6, 6.5, -1.7, -6.2, 7 ]; | |
| * print_r(nearest(-3.1, $a)); // idx = 7, delta = 0.6, val = -3.7 | |
| * print_r(nearest(7, $a)); // idx = 0, delta = 0, val = 7 | |
| * print_r(nearest(0, $a)); // idx = 11, delta = 1.7, val = -1.7 | |
| */ | |
| function nearest($needle, $haystack) { | |
| // do some basic check of inputs | |
| if (!is_array($haystack) || empty($haystack) || !is_numeric($needle)) { | |
| return false; | |
| } | |
| // I feel lucky | |
| $found = array_search($needle, $haystack, false); | |
| if ($found !== false) { | |
| return [ | |
| 'idx' => $found, | |
| 'delta' => 0, | |
| 'value' => $needle | |
| ]; | |
| } | |
| // digging deeper by binary search | |
| asort($haystack); // sort values first | |
| // check edge case: lover than the most low value | |
| $firstKey = key($haystack); | |
| if ($haystack[$firstKey] > $needle) { | |
| return [ | |
| 'idx' => $firstKey, | |
| 'delta' => abs($haystack[$firstKey] - $needle), | |
| 'value' => $haystack[$firstKey] | |
| ]; | |
| } | |
| // check edge case: bigger than the most biggest value | |
| $lastKey = key(array_slice($haystack, -1, 1, true)); // array_key_last($haystack); > php7.2 | |
| if ($haystack[$lastKey] < $needle) { | |
| return [ | |
| 'idx' => $lastKey, | |
| 'delta' => abs($needle - $haystack[$lastKey]), | |
| 'value' => $haystack[$lastKey] | |
| ]; | |
| } | |
| // digging trough array | |
| $orderedKeys = array_keys($haystack); | |
| $start = 0; | |
| $end = count($haystack) - 1; | |
| $nearest = ['key' => null, 'delta' => null]; | |
| $mid = null; | |
| while ($start <= $end) { | |
| // find middle index | |
| $mid = (int)floor(($start + $end) / 2); | |
| if ($needle < $haystack[$orderedKeys[$mid]]) { | |
| // move to the left side of the array | |
| $end = $mid -1; | |
| } | |
| else { | |
| // move to the right side of the array | |
| $start = $mid + 1; | |
| } | |
| $delta = abs($haystack[$orderedKeys[$mid]] - $needle); | |
| if (!isset($nearest['delta']) || $nearest['delta'] > $delta) { | |
| $nearest['key'] = $mid; | |
| $nearest['delta'] = $delta; | |
| } | |
| } | |
| return [ | |
| 'idx' => $orderedKeys[$nearest['key']], | |
| 'delta' => $nearest['delta'], | |
| 'val' => $haystack[$orderedKeys[$nearest['key']]] | |
| ]; | |
| } |
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