Data update

Task/Statistics-Basic/PHP/statistics-basic.php

@@ -0,0 +1,67 @@
+<?php
+// Statistics/Basic
+basic_stats(100);
+echo PHP_EOL;
+basic_stats(1000);
+echo PHP_EOL;
+basic_stats(10000);
+echo PHP_EOL;
+
+function basic_stats (int $sample_size) {
+  if ($sample_size < 1) return;
+  srand((double)microtime() * 1000000);
+  $r = array_fill(0, $sample_size, 0);
+  $h = array_fill(0, 10, 0);
+  $sum = 0.0;
+  $h_sum = 0;
+
+  // Generate '$sample_size' normally distributed random numbers with $mean 0.5
+  // and standard deviation 0.25
+  // calculate their $sum
+  // and in which box they will fall when drawing the histogram
+  for ($i = 0; $i < $sample_size; $i++) {
+    $r[$i] = mt_rand() / mt_getrandmax();
+    $sum += $r[$i];
+    $h[floor($r[$i] * 10)]++;
+  }
+
+  foreach ($h as $h_item)
+    $h_sum += $h_item;
+  // adjust one of the $h values if necessary to ensure $h_sum = $sample_size
+  $adj = $sample_size - $h_sum;
+  if ($adj != 0) {
+    for ($i = 0; $i < 10; $i++) {
+      $h[$i] += $adj;
+      if ($h[$i] >= 0) break;
+      $h[$i] -= $adj;
+    }
+  }
+  $mean = $sum / $sample_size;
+
+  $sum = 0.0;
+  // Now calculate their standard deviation
+  foreach ($r as $r_item)
+    $sum += pow($r_item - $mean, 2);
+  $sd = sqrt($sum / $sample_size);
+
+  // Draw a histogram of the data with interval 0.1
+  // If sample size > 300 then normalize histogram to 300
+  $scale = 1.0;
+  if ($sample_size > 500)
+    $scale = 500.0 / $sample_size;
+  echo 'Sample size '.$sample_size.PHP_EOL;
+  echo '  Mean '.
+    str_pad(number_format($mean, 6, '.', ''), 8, ' ', STR_PAD_LEFT).
+    '  SD '.
+    str_pad(number_format($sd, 6, '.', ''), 8, ' ', STR_PAD_LEFT).PHP_EOL;
+  $i = 0;
+  foreach ($h as $h_item) {
+    echo '  '.
+        str_pad(number_format($i / 10.0, 2, '.', ''), 4, ' ', STR_PAD_LEFT).
+        ' : ';
+    echo str_pad($h_item, 5, ' ', STR_PAD_LEFT).' '.
+      str_repeat('*', round($h_item * $scale)).PHP_EOL;
+    $i++;
+  }
+}
+?>