How to group rows with the same column value into one row in C?

Question

I am trying to make a statistic calculation code where a file with years are given on column1, type is given on column2 and count is given for column3. And finding the sum of counts for each type for each year.

I am stuck on grouping my data with same value in the column to be in the same row..

Input data:

2010    101     22
2010    101     40
2010    101     44
2010    101     66
2010    102     14
2010    100     7
2010    101     2
2010    101     3
2010    101     2
2010    101     3
2011    101     23
2011    101     27
2011    101     47
2011    101     66
2011    100     5
2011    102     16
2011    101     4
2011    101     1
2011    101     3
2011    101     5

Output:

| Year | 100 | 101 | 102 |
--------------------------
| 2010 |  7  | 182 |  14 |
| 2011 |  5  | 176 |  16 |

I could do

if(year == 2010)
{}
if(year == 2011)
{}

but my data is not going to always be like the given input. Is there a way to group them without knowing how many rows and what is going to be given in the year column? Maybe comparing row by row?

I'm confused, please help..

Answer 1

With a fixed/limited range for years and types, we can used a fixed size 2D array to hold the counts.

Here's some code that does that:

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

// year config
#define YRLO    2008
#define YRHI    2020
#define YRTOT   ((YRHI - YRLO) + 1)

// type config
#define TYPLO   100
#define TYPHI   103
#define TYPTOT  ((TYPHI - TYPLO) + 1)

#define RANGE(_val,_lo,_hi) \
    ((_val) >= (_lo)) && ((_val) <= (_hi))

int counts[YRTOT][TYPTOT];

int
main(void)
{

    const char *file = "data.txt";
    FILE *xfin = fopen(file,"r");

    if (xfin == NULL) {
        perror(file);
        exit(1);
    }

    int yr;
    int typ;
    int cnt;
    int lno = 0;

    while (fscanf(xfin,"%d %d %d",&yr,&typ,&cnt) == 3) {
        ++lno;

        if (! RANGE(yr,YRLO,YRHI)) {
            printf("line %d -- bad year -- %d\n",lno,yr);
            continue;
        }

        if (! RANGE(typ,TYPLO,TYPHI)) {
            printf("line %d -- bad type -- %d\n",lno,typ);
            continue;
        }

        // store data (convert absolute years and types to relative numbers)
        counts[yr - YRLO][typ - TYPLO] += cnt;
    }

    fclose(xfin);

    const char *fmt = " | %8d";

    int totlen = 0;

    // print the title
    totlen += printf("| Year");
    for (int tidx = 0;  tidx < TYPTOT;  ++tidx)
        totlen += printf(fmt,tidx + TYPLO);
    totlen += printf(" |");
    printf("\n");

    // print a dashed line
    for (int icol = 0;  icol < totlen;  ++icol)
        fputc('-',stdout);
    printf("\n");

    for (int yidx = 0;  yidx < YRTOT;  ++yidx) {
        // A nicety: decide if year has any non-zero counts
        int hasdata = 0;
        for (int tidx = 0;  tidx < TYPTOT;  ++tidx) {
            if (counts[yidx][tidx]) {
                hasdata = 1;
                break;
            }
        }

        // skip any years that have no data [optional]
        if (! hasdata)
            continue;

        // output the absolute year
        printf("| %d",yidx + YRLO);

        // output the counts for each type
        for (int tidx = 0;  tidx < TYPTOT;  ++tidx)
            printf(fmt,counts[yidx][tidx]);

        printf(" |\n");
    }

    return 0;
}

---

Here's the program output for your given input data:

| Year |      100 |      101 |      102 |      103 |
----------------------------------------------------
| 2010 |        7 |      182 |       14 |        0 |
| 2011 |        5 |      176 |       16 |        0 |