Cumulative standard deviation: Difference between revisions

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@@ Line 1,409: / Line 1,409: @@
 =={{header|Emacs Lisp}}==
+<lang lisp>(defun running-std (items)
-This implementation uses a temporary buffer (the central data structure of emacs) to have simple local variables.
+  (let ((running-sum 0)
+        (running-len 0)
+        (running-squared-sum 0)
+        (result 0))
+    (dolist (item items)
+      (setq running-sum (+ running-sum item))
+      (setq running-len (1+ running-len))
+      (setq running-squared-sum (+ running-squared-sum (* item item)))
+      (setq result (sqrt (- (/ running-squared-sum (float running-len))
+                            (/ (* running-sum running-sum)
+                               (float (* running-len running-len))))))
+      (message "%f" result))
+    result))
-<lang lisp>(defun running-std (x)
+(running-std '(2 4 4 4 5 5 7 9))</lang>
-  ; ensure that we have a float to avoid potential integer math errors.
-  (setq x (float x))
-  ; define variables to use
-  (defvar running-sum 0 "the running sum of all known values")
-  (defvar running-len 0 "the running number of all known values")
-  (defvar running-squared-sum 0 "the running squared sum of all known values")
-  ; and make them local to this buffer
-  (make-local-variable 'running-sum)
-  (make-local-variable 'running-len)
-  (make-local-variable 'running-squared-sum)
-  ; now process the new value
-  (setq running-sum (+ running-sum x))
-  (setq running-len (1+ running-len))
-  (setq running-squared-sum (+ running-squared-sum (* x x)))
-  ; and calculate the new standard deviation
-  (sqrt (- (/ running-squared-sum
-              running-len) (/ (* running-sum running-sum)
-                                 (* running-len running-len )))))</lang>
+{{out}}
-<lang lisp>(with-temp-buffer
-  (loop for i in '(2 4 4 4 5 5 7 9) do
-        (insert (number-to-string (running-std i)))
-        (newline))
-  (message (buffer-substring (point-min) (1- (point-max)))))
-"0.0
+.000000
-.0
+.000000
+.942809
-.9428090415820636
+.866025
-.8660254037844386
+.979796
-.9797958971132716
-.0
+.000000
+.399708
-.399708424447531
+.000000
-.0"</lang>
+.0
+{{libheader|Calc}}
-Emacs Lisp with built-in Emacs Calc
-<lang emacs-lisp>
+<lang lisp>(let ((x '(2 4 4 4 5 5 7 9)))
+  (string-to-number (calc-eval "sqrt(vpvar($1))" nil (append '(vec) x))))</lang>
-(setq x '[2 4 4 4 5 5 7 9])
-(string-to-number (calc-eval (format "sqrt(vpvar(%s))" x)))</lang>
+{{libheader|generator.el}}
-Emacs Lisp with generator library (introduced in Emacs 25.1)
-<lang emacs-lisp>
+<lang lisp>;; lexical-binding: t
 (require 'generator)
-(setq lexical-binding t)
 (iter-defun std-dev-gen (lst)
   (let ((sum 0)
-	(avg 0)
+        (avg 0)
-	(tmp '())
+        (tmp '())
-	(std 0))
+        (std 0))
     (dolist (i lst)
       (setq i (float i))
@@ Line 1,469: / Line 1,460: @@
       (setq std 0)
       (dolist (j tmp)
-	(setq std (+ std (expt (- j avg) 2))))
+        (setq std (+ std (expt (- j avg) 2))))
       (setq std (/ std (length tmp)))
       (setq std (sqrt std))
@@ Line 1,475: / Line 1,466: @@
 (let* ((test-data '(2 4 4 4 5 5 7 9))
-      (generator (std-dev-gen test-data)))
+       (generator (std-dev-gen test-data)))
   (dolist (i test-data)
-    (princ (format "with %d : " i))
+    (message "with %d: %f" i (iter-next generator))))</lang>
-    (princ (format "%f\n" (iter-next generator))))) </lang>
 =={{header|Erlang}}==