Data commit

Task/Cumulative-standard-deviation/Objective-C/cumulative-standard-deviation-1.m

@@ -0,0 +1,55 @@
+#import <Foundation/Foundation.h>
+
+@interface SDAccum : NSObject
+{
+  double sum, sum2;
+  unsigned int num;
+}
+-(double)value: (double)v;
+-(unsigned int)count;
+-(double)mean;
+-(double)variance;
+-(double)stddev;
+@end
+
+@implementation SDAccum
+-(double)value: (double)v
+{
+  sum += v;
+  sum2 += v*v;
+  num++;
+  return [self stddev];
+}
+-(unsigned int)count
+{
+  return num;
+}
+-(double)mean
+{
+  return (num>0) ? sum/(double)num : 0.0;
+}
+-(double)variance
+{
+  double m = [self mean];
+  return (num>0) ? (sum2/(double)num - m*m) : 0.0;
+}
+-(double)stddev
+{
+  return sqrt([self variance]);
+}
+@end
+
+int main()
+{
+  @autoreleasepool {
+
+    double v[] = { 2,4,4,4,5,5,7,9 };
+
+    SDAccum *sdacc = [[SDAccum alloc] init];
+
+    for(int i=0; i < sizeof(v)/sizeof(*v) ; i++)
+      printf("adding %f\tstddev = %f\n", v[i], [sdacc value: v[i]]);
+
+  }
+  return 0;
+}

Task/Cumulative-standard-deviation/Objective-C/cumulative-standard-deviation-2.m

@@ -0,0 +1,30 @@
+#import <Foundation/Foundation.h>
+
+typedef double (^Func)(double); // a block that takes a double and returns a double
+
+Func sdCreator() {
+  __block int n = 0;
+  __block double sum = 0;
+  __block double sum2 = 0;
+  return ^(double x) {
+    sum += x;
+    sum2 += x*x;
+    n++;
+    return sqrt(sum2/n - sum*sum/n/n);
+  };
+}
+
+int main()
+{
+  @autoreleasepool {
+
+    double v[] = { 2,4,4,4,5,5,7,9 };
+
+    Func sdacc = sdCreator();
+
+    for(int i=0; i < sizeof(v)/sizeof(*v) ; i++)
+      printf("adding %f\tstddev = %f\n", v[i], sdacc(v[i]));
+
+  }
+  return 0;
+}