The following task concerns data that came from a pollution monitoring station with twenty-four instruments monitoring twenty-four aspects of pollution in the air. Periodically a record is added to the file, each record being a line of 49 fields separated by white-space, which can be one or more space or tab characters.

The fields (from the left) are:

 DATESTAMP [ VALUEn FLAGn ] * 24

i.e. a datestamp followed by twenty-four repetitions of a floating-point instrument value and that instrument's associated integer flag. Flag values are >= 1 if the instrument is working and < 1 if there is some problem with it, in which case that instrument's value should be ignored.

A sample from the full data file readings.txt, which is also used in the Text processing/1 task, follows:

Data is no longer available at that link. Zipped mirror available here

1991-03-30	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1
1991-03-31	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	10.000	1	20.000	1	20.000	1	20.000	1	35.000	1	50.000	1	60.000	1	40.000	1	30.000	1	30.000	1	30.000	1	25.000	1	20.000	1	20.000	1	20.000	1	20.000	1	20.000	1	35.000	1
1991-03-31	40.000	1	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2	0.000	-2
1991-04-01	0.000	-2	13.000	1	16.000	1	21.000	1	24.000	1	22.000	1	20.000	1	18.000	1	29.000	1	44.000	1	50.000	1	43.000	1	38.000	1	27.000	1	27.000	1	24.000	1	23.000	1	18.000	1	12.000	1	13.000	1	14.000	1	15.000	1	13.000	1	10.000	1
1991-04-02	8.000	1	9.000	1	11.000	1	12.000	1	12.000	1	12.000	1	27.000	1	26.000	1	27.000	1	33.000	1	32.000	1	31.000	1	29.000	1	31.000	1	25.000	1	25.000	1	24.000	1	21.000	1	17.000	1	14.000	1	15.000	1	12.000	1	12.000	1	10.000	1
1991-04-03	10.000	1	9.000	1	10.000	1	10.000	1	9.000	1	10.000	1	15.000	1	24.000	1	28.000	1	24.000	1	18.000	1	14.000	1	12.000	1	13.000	1	14.000	1	15.000	1	14.000	1	15.000	1	13.000	1	13.000	1	13.000	1	12.000	1	10.000	1	10.000	1

Task

 Confirm the general field format of the file.
 Identify any DATESTAMPs that are duplicated.
 Report the number of records that have good readings for all instruments.


#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
 
typedef struct { const char *s; int ln, bad; } rec_t;
int cmp_rec(const void *aa, const void *bb)
{
	const rec_t *a = aa, *b = bb;
	return a->s == b->s ? 0 : !a->s ? 1 : !b->s ? -1 : strncmp(a->s, b->s, 10);
}
 
int read_file(const char *fn)
{
	int fd = open(fn, O_RDONLY);
	if (fd == -1) return 0;
 
	struct stat s;
	fstat(fd, &s);
 
	char *txt = malloc(s.st_size);
	read(fd, txt, s.st_size);
	close(fd);
 
	int i, j, lines = 0, k, di, bad;
	for (i = lines = 0; i < s.st_size; i++)
		if (txt[i] == '\n') {
			txt[i] = '\0';
			lines++;
		}
 
	rec_t *rec = calloc(sizeof(rec_t), lines);
	const char *ptr, *end;
	rec[0].s = txt;
	rec[0].ln = 1;
	for (i = 0; i < lines; i++) {
		if (i + 1 < lines) {
			rec[i + 1].s = rec[i].s + strlen(rec[i].s) + 1;
			rec[i + 1].ln = i + 2;
		}
		if (sscanf(rec[i].s, "%4d-%2d-%2d", &di, &di, &di) != 3) {
			printf("bad line %d: %s\n", i, rec[i].s);
			rec[i].s = 0;
			continue;
		}
		ptr = rec[i].s + 10;
 
		for (j = k = 0; j < 25; j++) {
			if (!strtod(ptr, (char**)&end) && end == ptr) break;
			k++, ptr = end;
			if (!(di = strtol(ptr, (char**)&end, 10)) && end == ptr) break;
			k++, ptr = end;
			if (di < 1) rec[i].bad = 1;
		}
 
		if (k != 48) {
			printf("bad format at line %d: %s\n", i, rec[i].s);
			rec[i].s = 0;
		}
	}
 
	qsort(rec, lines, sizeof(rec_t), cmp_rec);
	for (i = 1, bad = rec[0].bad, j = 0; i < lines && rec[i].s; i++) {
		if (rec[i].bad) bad++;
		if (strncmp(rec[i].s, rec[j].s, 10)) {
			j = i;
		} else
			printf("dup line %d: %.10s\n", rec[i].ln, rec[i].s);
	}
 
	free(rec);
	free(txt);
	printf("\n%d out %d lines good\n", lines - bad, lines);
	return 0;
}
 
int main()
{
	read_file("readings.txt");
	return 0;
}