k均值算法是模式識別的聚分類問題，這是用C實現其算法以下是程序源代碼



/****************************************************************************
*                                                   *
* KMEANS                                             *
*                                                   *
*****************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <conio.h>
#include <math.h>

// FUNCTION PROTOTYPES


// DEFINES
#define       SUCCESS       1
#define       FAILURE       0
#define       TRUE         1
#define       FALSE       0
#define       MAXVECTDIM     20
#define       MAXPATTERN     20
#define       MAXCLUSTER     10





char *f2a(double x, int width){
  char cbuf[255];
  char *cp;
  int i,k;
  int d,s;
cp=fcvt(x,width,&d,&s);
if (s) {
  strcpy(cbuf,"-");
  }
else {
  strcpy(cbuf," ");
  } /* endif */
if (d>0) {
  for (i=0; i<d; i++) {
    cbuf[i+1]=cp;
    } /* endfor */
  cbuf[d+1]=0;
  cp+=d;
  strcat(cbuf,".");
  strcat(cbuf,cp);
  } else {
    if (d==0) {
      strcat(cbuf,".");
      strcat(cbuf,cp);
      }
    else {
      k=-d;
      strcat(cbuf,".");
      for (i=0; i<k; i++) {
        strcat(cbuf,"0");
        } /* endfor */
      strcat(cbuf,cp);
      } /* endif */
  } /* endif */
cp=&cbuf[0];
return cp;
}




// ***** Defined structures & classes *****
struct aCluster {
  double     Center[MAXVECTDIM];
  int       Member[MAXPATTERN]; //Index of Vectors belonging to this cluster
  int       NumMembers;
};

struct aVector {
  double     Center[MAXVECTDIM];
  int       Size;
};

class System {
private:
  double     Pattern[MAXPATTERN][MAXVECTDIM+1];
  aCluster   Cluster[MAXCLUSTER];
  int       NumPatterns;       // Number of patterns
  int       SizeVector;       // Number of dimensions in vector
  int       NumClusters;       // Number of clusters
  void       DistributeSamples(); // Step 2 of K-means algorithm
  int       CalcNewClustCenters();// Step 3 of K-means algorithm
  double     EucNorm(int, int);   // Calc Euclidean norm vector
  int       FindClosestCluster(int); //ret indx of clust closest to pattern
                          //whose index is arg
public:
  system();
  int LoadPatterns(char *fname);     // Get pattern data to be clustered
  void InitClusters();           // Step 1 of K-means algorithm
  void RunKMeans();             // Overall control K-means process
  void ShowClusters();           // Show results on screen
  void SaveClusters(char *fname);   // Save results to file
  void ShowCenters();
};

void System::ShowCenters(){
int i,j;
printf("Cluster centers:\n");
for (i=0; i<NumClusters; i++) {
  Cluster.Member[0]=i;
  printf("ClusterCenter[%d]=(%f,%f)\n",i,Cluster.Center[0],Cluster.Center[1]);
  } /* endfor */
printf("\n");
}

int System::LoadPatterns(char *fname){
  FILE *InFilePtr;
  int   i,j;
  double x;
if((InFilePtr = fopen(fname, "r")) == NULL)
  return FAILURE;
fscanf(InFilePtr, "%d", &NumPatterns); // Read # of patterns
fscanf(InFilePtr, "%d", &SizeVector);   // Read dimension of vector
fscanf(InFilePtr, "%d", &NumClusters); // Read # of clusters for K-Means
for (i=0; i<NumPatterns; i++) {       // For each vector
  for (j=0; j<SizeVector; j++) {     // create a pattern
    fscanf(InFilePtr,"%lg",&x);     // consisting of all elements
    Pattern[j]=x;
    } /* endfor */
  } /* endfor */
printf("Input patterns:\n");
for (i=0; i<NumPatterns; i++) {
  printf("Pattern[%d]=(%2.3f,%2.3f)\n",i,Pattern[0],Pattern[1]);
  } /* endfor */
printf("\n--------------------\n");
return SUCCESS;
}
//***************************************************************************
// InitClusters                                         *
//   Arbitrarily assign a vector to each of the K clusters             *
//   We choose the first K vectors to do this                     *
//***************************************************************************
void System::InitClusters(){
int i,j;
printf("Initial cluster centers:\n");
for (i=0; i<NumClusters; i++) {
  Cluster.Member[0]=i;
  for (j=0; j<SizeVector; j++) {
    Cluster.Center[j]=Pattern[j];
    } /* endfor */
  } /* endfor */
for (i=0; i<NumClusters; i++) {
  printf("ClusterCenter[%d]=(%f,%f)\n",i,Cluster.Center[0],Cluster.Center[1]);
  } /* endfor */
printf("\n");
}

void System::RunKMeans(){
int converged;
int pass;
pass=1;
converged=FALSE;
while (converged==FALSE) {
  printf("PASS=%d\n",pass++);
  DistributeSamples();
  converged=CalcNewClustCenters();
  ShowCenters();
  } /* endwhile */
}

double System::EucNorm(int p, int c){   // Calc Euclidean norm of vector difference
double dist,x;                 // between pattern vector, p, and cluster
int i;                       // center, c.
char zout[128];
char znum[40];
char *pnum;

pnum=&znum[0];
strcpy(zout,"d=sqrt(");
printf("The distance from pattern %d to cluster %d is calculated as:\n",c,p);
dist=0;
for (i=0; i<SizeVector ;i++){
  x=(Cluster[c].Center-Pattern[p])*(Cluster[c].Center-Pattern[p]);
  strcat(zout,f2a(x,4));
  if (i==0)
    strcat(zout,"+");
  dist += (Cluster[c].Center-Pattern[p])*(Cluster[c].Center-Pattern[p]);
  } /* endfor */
printf("%s)\n",zout);
return dist;
}

int System::FindClosestCluster(int pat){
  int i, ClustID;
  double MinDist, d;
MinDist =9.9e+99;
ClustID=-1;
for (i=0; i<NumClusters; i++) {
  d=EucNorm(pat,i);
  printf("Distance from pattern %d to cluster %d is %f\n\n",pat,i,sqrt(d));
  if (d<MinDist) {
    MinDist=d;
    ClustID=i;
    } /* endif */
  } /* endfor */
if (ClustID<0) {
  printf("Aaargh");
  exit(0);
  } /* endif */
return ClustID;
}

void System::DistributeSamples(){
int i,pat,Clustid,MemberIndex;
//Clear membership list for all current clusters
for (i=0; i<NumClusters;i++){
  Cluster.NumMembers=0;
  }
for (pat=0; pat<NumPatterns; pat++) {
  //Find cluster center to which the pattern is closest
  Clustid= FindClosestCluster(pat);
  printf("patern %d assigned to cluster %d\n\n",pat,Clustid);
  //post this pattern to the cluster
  MemberIndex=Cluster[Clustid].NumMembers;
  Cluster[Clustid].Member[MemberIndex]=pat;
  Cluster[Clustid].NumMembers++;
  } /* endfor */
}

int System::CalcNewClustCenters(){
  int ConvFlag,VectID,i,j,k;
  double tmp[MAXVECTDIM];
  char xs[255];
  char ys[255];
  char nc1[20];
  char nc2[20];
  char *pnc1;
  char *pnc2;
  char *fpv;

pnc1=&nc1[0];
pnc2=&nc2[0];
ConvFlag=TRUE;
printf("The new cluster centers are now calculated as:\n");
for (i=0; i<NumClusters; i++) {         //for each cluster
  pnc1=itoa(Cluster.NumMembers,nc1,10);
  pnc2=itoa(i,nc2,10);
  strcpy(xs,"Cluster Center");
  strcat(xs,nc2);
  strcat(xs,"(1/");
  strcpy(ys,"(1/");
  strcat(xs,nc1);
  strcat(ys,nc1);
  strcat(xs,")(");
  strcat(ys,")(");
  for (j=0; j<SizeVector; j++) {         // clear workspace
    tmp[j]=0.0;
    } /* endfor */
  for (j=0; j<Cluster.NumMembers; j++) { //traverse member vectors
    VectID=Cluster.Member[j];
    for (k=0; k<SizeVector; k++) {       //traverse elements of vector
      tmp[k] += Pattern[VectID][k];     // add (member) pattern elmnt into temp
      if (k==0) {
        strcat(xs,f2a(Pattern[VectID][k],3));
        } else {
        strcat(ys,f2a(Pattern[VectID][k],3));
        } /* endif */
      } /* endfor */
    if(j<Cluster.NumMembers-1){
      strcat(xs,"+");
      strcat(ys,"+");
      }
    else {
      strcat(xs,")");
      strcat(ys,")");
      }
    } /* endfor */
  for (k=0; k<SizeVector; k++) {         //traverse elements of vector
    tmp[k]=tmp[k]/Cluster.NumMembers;
    if (tmp[k] != Cluster.Center[k])
      ConvFlag=FALSE;
    Cluster.Center[k]=tmp[k];
    } /* endfor */
  printf("%s,\n",xs);
  printf("%s\n",ys);
  } /* endfor */
return ConvFlag;
}

void System::ShowClusters(){
  int cl;
for (cl=0; cl<NumClusters; cl++) {
  printf("\nCLUSTER %d ==>[%f,%f]\n", cl,Cluster[cl].Center[0],Cluster[cl].Center[1]);
  } /* endfor */
}

void System::SaveClusters(char *fname){
}


main(int argc, char *argv[]) {
  System kmeans;
if (argc<2) {
  printf("USAGE: KMEANS PATTERN_FILE\n");
  exit(0);
  }
if (kmeans.LoadPatterns(argv[1])==FAILURE ){
  printf("UNABLE TO READ PATTERN_FILE:%s\n",argv[1]);
  exit(0);
  }
kmeans.InitClusters();
kmeans.RunKMeans();
kmeans.ShowClusters();
}