Er, either the php-internals MARC archive doesn't show all attachments, or
my diff file got stripped en route for not having a .txt extension. I've
attached it again, just to make sure.
Paul
--
-----Original Message-----
From: Paul Hudson [mailto:[EMAIL PROTECTED]
Sent: 10 February 2004 00:30
To: '[EMAIL PROTECTED]'
Subject: [PATCH] Bug #24064: Standard deviation
Hi there,
Bug #24064 (submitted by [EMAIL PROTECTED]) requests a standard deviation
function for PHP. I realise that any of you could implement this in 10
minutes, but according to the bug database it is still Open so I figured I
would give it a try myself!
There are probably a dozen errors in the code and/or places where it could
be better optimised, but I'm hoping one of you might be able to help with
that. So, the attached diff file implements the function array_std_dev(),
to calculate standard deviation using the deviation method.
With the function in place, standard deviation is calculated like this:
<?php
$scores = array(18,5,7,18,3,2,10);
print array_std_dev($score);
// prints 6.6833125519211
?>
My first attempt at implementing this was using an extra array to buffer the
deviations - this was more out of curiosity to see how the array stuff
works. Sadly, it caused PHP to segfault and I couldn't figure out why - can
any of you help me spot the brain fart? (I've attached the offending code
in bad_stddev_code.txt)
Yours,
Paul
PS: I'm not on the internals list, so I would appreciate it if you would CC
me on your reply.
diff -rubB php-snap/ext/standard/array.c php-new/ext/standard/array.c
--- php-snap/ext/standard/array.c 2004-01-28 21:08:16.000000000 +0000
+++ php-new/ext/standard/array.c 2004-02-09 23:57:14.590206400 +0000
@@ -4229,6 +4229,77 @@
}
/* }}} */
+
+/* {{{ proto mixed array_std_dev(array input)
+ Returns the standard deviation of the array entries */
+PHP_FUNCTION(array_std_dev)
+{
+ zval **input,
+ **entry,
+ *entry_n;
+ int argc = ZEND_NUM_ARGS();
+ HashPosition pos;
+ double total = 0;
+ double mean;
+ int numelements = 0; // note this is calcuated by hand, not using
zend_hash_num_elements()
+ double deviation = 0;
+
+ if (argc != 1 || zend_get_parameters_ex(argc, &input) == FAILURE) {
+ WRONG_PARAM_COUNT;
+ }
+
+ if (Z_TYPE_PP(input) != IS_ARRAY) {
+ php_error_docref(NULL TSRMLS_CC, E_WARNING, "The argument should be an
array");
+ return;
+ }
+
+ ZVAL_LONG(return_value, 0);
+
+ // step one: sum the values of the array
+ for (zend_hash_internal_pointer_reset_ex(Z_ARRVAL_PP(input), &pos);
+ zend_hash_get_current_data_ex(Z_ARRVAL_PP(input), (void **)&entry,
&pos) == SUCCESS;
+ zend_hash_move_forward_ex(Z_ARRVAL_PP(input), &pos)) {
+
+ if (Z_TYPE_PP(entry) == IS_ARRAY || Z_TYPE_PP(entry) == IS_OBJECT)
+ continue;
+
+ entry_n = *entry;
+ zval_copy_ctor(entry_n);
+ convert_scalar_to_number(entry_n TSRMLS_CC);
+ convert_to_double(entry_n);
+ total += Z_DVAL_P(entry_n);
+
+ // this is incremented by hand so that it doesn't count object and
array elements as an element
+ numelements++;
+ }
+
+ // step two: calculate the mean of the input array
+ mean = total / numelements;
+
+ // step three: add up the squared deviations for each array element
+ total = 0;
+
+ for (zend_hash_internal_pointer_reset_ex(Z_ARRVAL_PP(input), &pos);
+ zend_hash_get_current_data_ex(Z_ARRVAL_PP(input), (void **)&entry,
&pos) == SUCCESS;
+ zend_hash_move_forward_ex(Z_ARRVAL_PP(input), &pos)) {
+
+ if (Z_TYPE_PP(entry) == IS_ARRAY || Z_TYPE_PP(entry) == IS_OBJECT)
+ continue;
+
+ entry_n = *entry;
+ zval_copy_ctor(entry_n);
+ convert_scalar_to_number(entry_n TSRMLS_CC);
+ convert_to_double(entry_n);
+ deviation = Z_DVAL_P(entry_n) - mean;
+ total += deviation * deviation;
+ }
+
+ // step four: divide the sum of the squared deviation array by the number of
elements - 1
+ total /= numelements - 1;
+ ZVAL_DOUBLE(return_value, sqrt(total));
+}
+/* }}} */
+
/*
* Local variables:
* tab-width: 4
diff -rubB php-snap/ext/standard/basic_functions.c
php-new/ext/standard/basic_functions.c
--- php-snap/ext/standard/basic_functions.c 2004-01-19 19:11:00.000000000 +0000
+++ php-new/ext/standard/basic_functions.c 2004-02-09 18:16:31.314160000 +0000
@@ -794,6 +794,7 @@
PHP_FE(array_chunk,
NULL)
PHP_FE(array_combine,
NULL)
PHP_FE(array_key_exists,
NULL)
+ PHP_FE(array_std_dev,
NULL)
/* aliases from array.c */
PHP_FALIAS(pos, current,
first_arg_force_ref)
diff -rubB php-snap/ext/standard/php_array.h php-new/ext/standard/php_array.h
--- php-snap/ext/standard/php_array.h 2004-01-08 18:07:44.000000000 +0000
+++ php-new/ext/standard/php_array.h 2004-02-09 18:15:27.892964800 +0000
@@ -93,6 +93,7 @@
PHP_FUNCTION(array_key_exists);
PHP_FUNCTION(array_chunk);
PHP_FUNCTION(array_combine);
+PHP_FUNCTION(array_std_dev);
HashTable* php_splice(HashTable *, int, int, zval ***, int, HashTable **);
PHPAPI int php_array_merge(HashTable *dest, HashTable *src, int recursive TSRMLS_DC);
--
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