remove previous_values and added period param

README.md

@@ -16,22 +16,15 @@ or add `romulodl/ema` to your `composer.json`. Please check the latest version i
 
 ```php
 $ema = new Romulodl\Ema();
-$ema->calculate(array $values, array $previous_values = []);
+$ema->calculate(array $values, int $period = 9);
 ```
 
 For example:
 ```php
 $ema = new Romulodl\Ema();
-$ema->calculate([10, 12, 14, 20, 14, 10, 11]);
+$ema->calculate([10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]);
 ```
 
-#### What is `$previous_values` for?
-
-The EMA calculation is based on the previous round of calculation. The `n` round depends on `n - 1` result.
-Then what is `n - 1` for the first round? If `$previous_values` is not available, it uses a simple moving average
-for it. With `$previous_values` set, it will start the calculation of the EMA before and the result will be more
-accurate (at least closest to what TradingView shows.)
-
 ## Why did you do this?
 
 The PECL Trading extension is crap and not everyone wants to install it.

src/Ema.php

@@ -11,46 +11,31 @@ class Ema
 	 * The previous values options exists to try to smooth the current calculation
 	 * if it is empty, it will calculate the SMA for the first round.
 	 */
-	public function calculate(array $values, array $previous_values = []) : float
+	public function calculate(array $values, int $period = 9) : float
 	{
-		if (empty($values)) {
+		if (empty($values) || count($values) < $period) {
 			throw new \Exception('[' . __METHOD__ . '] $values parameters is empty');
 		}
 
-		$mult = 2 / (count($values) + 1);
-
-		return $this->calculate_ema($values, $mult, $previous_values);
-	}
-
-	private function calculate_ema(
-		array $values,
-		float $mult,
-		array $previous_values = [],
-		$prev = false
-	): float
-	{
+		$mult = 2 / ($period + 1);
+		$prev_close = [];
+		$prev_ema = false;
 		foreach ($values as $value) {
 			if ( !is_numeric($value)) {
 				throw new \Exception('[' . __METHOD__ . '] invalid value: '. $value);
 			}
 
-			if (!$prev) {
-				$prev = !empty($previous_values) ?
-					$this->calculate_ema($previous_values, $mult) :
-					$this->sma($values);
-
+			if (count($prev_close) < $period) {
+				$prev_close[] = $value;
+				if (count($prev_close) === $period) {
+					$prev_ema = array_sum($prev_close) / $period;
+				}
 				continue;
 			}
 
-			$prev = ($value - $prev) * $mult + $prev;
+			$prev_ema = ($value - $prev_ema) * $mult + $prev_ema;
 		}
 
-		return $prev;
+		return $prev_ema;
 	}
-
-	private function sma(array $values) : float
-	{
-		return array_sum($values) / count($values);
-	}
-
 }

tests/TestEma.php

@@ -8,88 +8,27 @@ final class EmaTest extends TestCase
 {
 	public function testCalculateEmaWithEmptyPreviousValues(): void
 	{
-		$values = [
-			9148.27,
-			9995,
-			9807.49,
-			9550.67,
-			8719.53,
-			8561.09,
-			8808.71,
-			9305.91,
-			9786.80,
-			9310.73
-		];
+		$val = require(__DIR__ . '/values.php');
+		$values = [];
+		foreach ($val as $v) {
+			$values[] = $v[2];
+		}
+		$values = array_slice($values, -9);
 
 		$ema = new Ema();
-		$this->assertSame(9288.86, round($ema->calculate($values), 2));
-	}
-
-	public function testCalculateEmaWithPreviousValues(): void
-	{
-		$previous_values = [
-			7694.17,
-			7774,
-			7735.75,
-			8784.20,
-			8624.76,
-			8830.52,
-			8975.18,
-			8900,
-			8873.98,
-			9022.78
-		];
-
-		$values = [
-			9148.27,
-			9995,
-			9807.49,
-			9550.67,
-			8719.53,
-			8561.09,
-			8808.71,
-			9305.91,
-			9786.80,
-			9310.73
-		];
-
-		$ema = new Ema();
-		$this->assertSame(9197.01, round($ema->calculate($values, $previous_values), 2));
+		$this->assertSame(9147.33, round($ema->calculate($values), 2));
 	}
 
 	public function testCalculateEmaWithMorePreviousValues(): void
 	{
-		$previous_values = [
-			7483.35,
-			7504.11,
-			7534.01,
-			7694.17,
-			7774,
-			7735.75,
-			8784.20,
-			8624.76,
-			8830.52,
-			8975.18,
-			8900,
-			8873.98,
-			9022.78
-		];
-
-		$values = [
-			9148.27,
-			9995,
-			9807.49,
-			9550.67,
-			8719.53,
-			8561.09,
-			8808.71,
-			9305.91,
-			9786.80,
-			9310.73
-		];
+		$val = require(__DIR__ . '/values.php');
+		$values = [];
+		foreach ($val as $v) {
+			$values[] = $v[2];
+		}
 
 		$ema = new Ema();
-		$this->assertSame(9182.18, round($ema->calculate($values, $previous_values), 2));
+		$this->assertSame(9101.36, round($ema->calculate($values), 2));
 	}
 
 	public function testCalculateEmaWithEmptyArray(): void
@@ -112,7 +51,6 @@ public function testCalculateEmaWithInvalidArray(): void
 			8808.71,
 			9305.91,
 			9786.80,
-			9310.73
 		];
 
 		$this->expectException(Exception::class);