Sort 1-D of a 2-D array and copy both

[IN_C_CRADDLE]

Hello all,
I am newbie trying to sort as follows :

Before:
int a[9][2] = {0,5,
0,10,
1,2,
0,1,
0,8,
1,9,
1,12,
0,11,
0,15};

After Sorting:

a[9][2] = {
0,1,
1,2,
0,5,
0,8,
1,9,
0,10,
0,11,
1,12,
0,15};

I want to sort a[][1] in in ascending order and copy both a[][0] and a[][1].
Please help me.

~regards,
Dilip

 

[Michael Mair]

Hiho,

Hello all,
I am newbie trying to sort as follows :

Before:
int a[9][2] = {0,5,
0,10,
1,2,
0,1,
0,8,
1,9,
1,12,
0,11,
0,15};

After Sorting:

a[9][2] = {
0,1,
1,2,
0,5,
0,8,
1,9,
0,10,
0,11,
1,12,
0,15};

I want to sort a[][1] in in ascending order and copy both a[][0] and a[][1].

Do you mean you want to sort using "a[][1]" as sort key and the
arrays of two integers to be sorted?

Then use qsort() from <stdlib.h> and give it a suitable compar()
function:
#include <stdlib.h>
void qsort(void *base, size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
Read the manpage or the documentation in a C book of your choice.

Here:

base: a
nmemb: 9
size: 2*sizeof(int)
compar: pointer to a function comparing two objects
e.g.
int cmp_comp1 (const void *a, const void *b)
{
int val_a, val_b;

val_a = ((const int *) a)[1];
val_b = ((const int *) b)[1];

if (val_a < val_b)
return -1;
else if (val a > val b)
return 1;
else return 0;
}

I did not test the code, but I think you can get the idea from
what I wrote.


Cheers
Michael

 

[hari4063]

You can do this by writing your own sort, like:

void sort(int a[][2], int len) {
int i, j, tmp;
for(i=0; i<len; i++)
for(j=i+1; j<len; j++)
if (a[1] > a[j][1]) {
tmp=a[1]; a[1]=a[j][1];
a[j][1]=tmp;
}
}

of course, find some better algo (like Quick Sort).

 

[Flash Gordon]

On 27 Oct 2004 05:41:03 -0700

Hello all,
I am newbie trying to sort as follows :

Before:
int a[9][2] = {0,5,

I want to sort a[][1] in in ascending order and copy both a[][0] and
a[][1]. Please help me.

Sounds a lot like homework to me. I'll do it for 100UKP (normally you
get charged in the UK as if the exchange rate with the USD was 1).

Alternatively you could try looking up sorting in K&R (read the FAQ for
comp.lang.c if you don't know what K&R is, and read it anyway even if
you do) or any other text book, then come back here with your attempt at
implementing it once you have made the attempt.

 

[Barry Schwarz]

You can do this by writing your own sort, like:

void sort(int a[][2], int len) {
int i, j, tmp;
for(i=0; i<len; i++)
for(j=i+1; j<len; j++)
if (a[1] > a[j][1]) {
tmp=a[1]; a[1]=a[j][1];
a[j][1]=tmp;

Since he wants to keep each a[n][0]-a[n][1] pair together, you need to
also swap a[0] with a[j][0] just as you did for a[1] and
a[j][1].

}
}

of course, find some better algo (like Quick Sort).

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