Ibrahim F Haddad wrote:
> Given a file that contains data of the following format:
>
> 7.606565 5.404950
> 4.969272 4.597600
> 4.969272 4.597600
> 2.400000 3.486746
> 3.000000 3.672252
> 3.600000 3.766663
>
>
> How to sort it in increasing order of the x column so
> after sorting it looks like that:
>
> 2.400000 3.486746
> 3.000000 3.672252
> 3.600000 3.766663
> 4.969272 4.597600
> 4.969272 4.597600
> 7.606565 5.404950
>
> please note that duplicate entries may exist.
In this specific case, you could just sort the file with `sort -n'.
More generally, you can sort arbitrary data using the `qsort'
function, which is part of the ANSI C standard library (qsort is
declared in stdlib.h).
Supposing you have read the data into an array of doubles, where row i
is stored in elements 2i and 2i+1, you can sort the array using:
static int compare(const void *pa, const void *pb)
{
double a = *(const double *)pa;
double b = *(const double *)pb;
if (a < b)
return -1;
if (a > b)
return 1;
return 0;
}
void sort_it(double *data, int rows)
{
qsort(data, rows, 2*sizeof(double), compare);
}
--
Glynn Clements <[EMAIL PROTECTED]>
