• dsimcha <dsimcha yahoo.com> Jul 06 2008
• bearophile <bearophileHUGS mailas.com> Jul 06 2008
• superdan <super dan.org> Jul 06 2008

dsimcha <dsimcha yahoo.com> writes:

I've been working on implementing some statistics functions in D, and noticed
that it would be nice if a multisort function were in Phobos.  Such a function
would take N arrays in and sort them by the first one.  The common way to
handle something like this seems to be to make a struct with the fields, make
opCmp point to whatever field you want to sort by, and then use a regular
sorting algorithm.  This is slow and a pain.  I've implemented a few different
multisort functions, along with documentation and unit testing, and would like
to contribute them to Phobos.  I've attached the source file and the Ddoc
documentation.

bearophile <bearophileHUGS mailas.com> writes:

I haven't tried your code (yet), but I suggest you to not use too much long
lines (90-100 chars is probably enough).

Your code contains both the forms:
    foreach(ti, array; data) temp[ti][index] = array[$-1];
    ...
    foreach(i, array; temp) {
        data[i][0..$] = array[0..$];
    }

I suggest you to use the second form, or the following one if you want to save
a line:
    foreach (i, array; temp)
        data[i][0..$] = array[0..$];

I suggest you to avoid writing a single large unittest, but to add one block of
unittests under each function/class/method, so you can isolate them better,
disable them, etc (even better is having a standard way to give them a name, so
the program/compiler that executes the unit tests knows what
function/class/method are broken. D unittest system needs just small
improvements to become good enough for small/medium size programs).

Bye,
bearophile

superdan <super dan.org> writes:

dsimcha Wrote:

 I've been working on implementing some statistics functions in D, and noticed
 that it would be nice if a multisort function were in Phobos.  Such a function
 would take N arrays in and sort them by the first one.  The common way to
 handle something like this seems to be to make a struct with the fields, make
 opCmp point to whatever field you want to sort by, and then use a regular
 sorting algorithm.  This is slow and a pain.  I've implemented a few different
 multisort functions, along with documentation and unit testing, and would like
 to contribute them to Phobos.  I've attached the source file and the Ddoc
 documentation.


yarp i needed this 2. sounds good but it's unnecessary. sort does all that shit
easily.

int[] arr1;
float[] arr2;
string[] arr3;
// sort three arrays as one
void mySwap(int* a, int* b)
{
    auto i = a - arr1.ptr, j = b - arr1.ptr;
    iterSwap(a, b);
    swap(arr2[i], arr2[j]);
    swap(arr3[i], arr3[j]);
}
sort!("a < b", SwapStrategy.unstable, mySwap)(arr1);

what happens is that whenever two doods in arr1 get swapped, the corresponding
doods in arr2 and arr3 get swapped too. i don't know why the docs don't give
such examples. there's just a hint "Possible uses include notifying observers,
counting the number of operations, or manipulating multiple collections in
lockstep." the lockstep thing gave it away.

& of course you deserve shoe heel beating for putting bubblesort in there. no
matter how much you warn against its usage.