MaplePrimes - answers and comments on Question, Sorting a list of xy pairs

sort

pagan — Wed, 19 May 2010 17:17:57 Z

Is this what you want?

> a := [[1, 7], [2, 3], [5, 4], [1, 2], [8, 9], [7, 9], [1, 6]]:

> sort(a, (x, y) -> x[1]<y[1] or (x[1]=y[1] and x[2]<y[2]) );
           [[1, 2], [1, 6], [1, 7], [2, 3], [5, 4], [7, 9], [8, 9]]

sort

Scott03 — Wed, 19 May 2010 17:21:51 Z

Is this what you want?

> sort(a, (x, y) ->`if`(x[1] = y[1], evalb(x[2] < y[2]), evalb(x[1] < y[1])));

Scott

Yes, sort in ascending order for plot

Christopher2222 — Wed, 19 May 2010 17:30:40 Z

Yes, to sort them in an ascending order so plotting will be continuously increasing.

Thanks for those two variations.

sort

alec — Wed, 19 May 2010 18:04:03 Z

In Maple 13+, sort without additional arguments should work like that,

sort(a);

       [[1, 2], [1, 6], [1, 7], [2, 3], [5, 4], [7, 9], [8, 9]]

Alec

evalb

pagan — Wed, 19 May 2010 18:22:05 Z

Maple will apply the evalb automatically here, so those evalb's are a (small but) unnecessary additional cost. There may be much more efficient ways to do this task for very large listlists, so it doesn't matter much here.

But in general you want to avoid programming anything like this too

if evalb(....) then ...

sorting a list of lists in Maple 12 or inferior.

xavier — Wed, 19 May 2010 21:43:44 Z

here is a solution for sorting a list of lists of numbers for Maple versions inferior to Maple 12.

I supposed that [1,2] is inferior to [1,2,1] or [1,2,3]. etc...

plus := proc (l, d) local e, i; e := 0; for i to min(nops(l),nops(d)) do if l[i] < d[i] then e := l; break elif d[i] < l[i] then e := d; break end if end do; if e = 0 then if nops(d) <= nops(l) then e := d else e := l end if end if; return e end proc;

plus([1,3],[1,2,3]);
[1, 2, 3]

mini := proc (L) local x, i; x := L[1]; for i from 2 to nops(L) do x := plus(x,L[i]) end do; return x end proc;

soust := proc (l, d0) local A, d, i, e, D, j; A := []; d := d0; for i to nops(l) do e := 0; D := d; for j to nops(d) do if l[i] = d[j] then e := 1; D := [seq(D[k],k = 1 .. j-1), seq(D[k],k = j+1 .. nops(D))]; break end if end do; if e = 0 then A := [op(A), l[i]] end if; d := D end do; return A end proc;

ord := proc (L0) local L, A, i; L := L0; A := []; for i to nops(L) do A := [op(A), mini(L)]; L := soust(L,[A[nops(A)]]) end do; return A end proc;

ord([[1,3],[1,2],[1,2,3],[3,2],[3,1],[3,1,2]]);
[[1, 2], [1, 2, 3], [1, 3], [3, 1], [3, 1, 2], [3, 2]]

a := [[1, 7], [2, 3], [5, 4], [1, 2], [8, 9], [7, 9], [1, 6]]:ord(a);

[[1, 2], [1, 6], [1, 7], [2, 3], [5, 4], [7, 9], [8, 9]]