上次講了使用Excel的巨集進行Excel資料和libsvm資料之間的轉換，但是對於大資料量情況下，該方法並不好用，因此需要使用程式來實現。
非常幸運在libsvm官網上找到了C程式可以做這個事情，試用了一下後覺得有一些問題，因此對源程式進行了修改，在此分享給大家。
主要的改進點如下：
1、原來的程式計算後資料輸出在控制檯，不方便進行進一步操作，因此 將輸出改成寫入了TXT檔案。
2、解決了double型資料後有過多的0（如4.0000）的顯示問題。
3、解決了cvs原始資料lable在最後一列導致輸出的libsvm檔案屬性和label相反的問題。
原始碼如下，作為參考。

/*
    convert cvs data to libsvm/svm-light format
 

    Updated on Jan 11, 2014 to use strsep() instead of strtok().
*/

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

#ifndef __USE_BSD
char *strsep(char **stringp, const char *delim);
#endif

char buf[10000000];
float feature[100000];

int main(int argc, char **argv)
{
    FILE *fp,*fp1
 
;

    if(argc!=2) { fprintf(stderr,"Usage %s filename\n",argv[0]); }
/*  if((fp=fopen(argv[1],"r"))==NULL)
//在命令列跑程式可以使用這段，將檔案路徑直接作為main函式的引數就行了
    {
        fprintf(stderr,"Can't open input file %s\n",argv[1]);
    }
*/

    if((fp=fopen("day.csv","r"))==NULL)//我的輸入檔案
    {
        fprintf(stderr,"Can't open input file %s
 
\n",argv[1]);
    }
     if((fp1=fopen("1.txt","w"))==NULL)//輸出檔案
    {
        printf("Can't open input file %s\n");
    }

    while(fscanf(fp,"%[^\n]\n",buf)==1)
    {
        int i=0,j;
        char *ptr=buf;
        while (ptr != NULL)
        {
            char *token = strsep(&ptr, ",");
            if (strlen(token) == 0)
                feature[i++] = 0.0;
            else
                feature[i++] = atof(token);
        }

    fprintf(fp1,"%d ", (int) feature[i-1]);
        for(j=0;j<i-1;j++)
            if(feature[j]!=0)
                //printf(" %d:%f",j,feature[j]);
                 fprintf(fp1," %d:%g",j+1,feature[j]);

        //printf("\n");
        fprintf(fp1,"\n");
    }
    fclose(fp1);
    return 0;
}

#ifndef __USE_BSD
/*-
 * Copyright (c) 1990, 1993
 *  The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
char *strsep(char **stringp, const char *delim){
    char *s;
    const char *spanp;
    int c, sc;
    char *tok;

    if ((s = *stringp) == NULL)
        return (NULL);
    for (tok = s;;) {
        c = *s++;
        spanp = delim;
        do {
            if ((sc = *spanp++) == c) {
                if (c == 0)
                    s = NULL;
                else
                    s[-1] = 0;
                *stringp = s;
                return (tok);
            }
        } while (sc != 0);
    }
}
#endif