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# Sorting Multiple Arrays Together in C++

jpoloney@gmail.com
Guest
Posts: n/a

 03-27-2006
I was wondering if there was a quick and easy way to sort multiple
arrays in C++. What I mean is that, say I have 3 integer arrays. They
are in order by array indices (array1[0] corresponds to array2[0] and
array3[0], etc). I want to do something exactly like the Excel sort of
"Sort by A, then by B, then by C". Meaning, sort array A in ascending
order, then inside of that sort B in ascending order, etc. Here is some
pseudo code for what I'm trying to do:

array1 = [1, 1, 2, 2, 3, 3];
array2 = [2, 1, 2, 1, 2, 1];
array3 = [1, 2, 3, 4, 5, 6];

sort_1_then_2_then_3();

array1 = [1, 1, 2, 2, 3, 3];
array2 = [1, 2, 1, 2, 1, 2];
array3 = [2, 1, 4, 3, 6, 5];

Is there anyway to do this using STL sorts in C++ or would I have to
write this algorithm from scratch?

Daniel T.
Guest
Posts: n/a

 03-27-2006
In article <(E-Mail Removed). com>,
http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:

> I was wondering if there was a quick and easy way to sort multiple
> arrays in C++. What I mean is that, say I have 3 integer arrays. They
> are in order by array indices (array1[0] corresponds to array2[0] and
> array3[0], etc). I want to do something exactly like the Excel sort of
> "Sort by A, then by B, then by C". Meaning, sort array A in ascending
> order, then inside of that sort B in ascending order, etc. Here is some
> pseudo code for what I'm trying to do:
>
> array1 = [1, 1, 2, 2, 3, 3];
> array2 = [2, 1, 2, 1, 2, 1];
> array3 = [1, 2, 3, 4, 5, 6];
>
> sort_1_then_2_then_3();
>
> array1 = [1, 1, 2, 2, 3, 3];
> array2 = [1, 2, 1, 2, 1, 2];
> array3 = [2, 1, 4, 3, 6, 5];
>
> Is there anyway to do this using STL sorts in C++ or would I have to
> write this algorithm from scratch?

If you can rearrange your data so that you have one array that contains
objects that have three elements each, then you can use the standard
library functions to do the job using lexicographical_compare and sort.

struct Type {
int rep[3];
};

friend bool operator<( const Type& lhs, const Type& rhs ) {
return lexicographical_compare( lhs.rep, lhs.rep + 3,
rhs.rep, rhs.rep + 3 );
}

Type array[6];
(load the array up with the data.)

sort( array, array + 6 );

--
Magic depends on tradition and belief. It does not welcome observation,
nor does it profit by experiment. On the other hand, science is based
on experience; it is open to correction by observation and experiment.

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