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+--- Thread: Sorting a matrix? (/thread-4176.html)
Sorting a matrix? - DrD - 06-18-2015 01:48 PM
Looking for ideas:
I need to row sort M1, an (n x 4) matrix, in decreasing order of column 4. Then on decreasing order of column 2, if sorted M1 contains more than one row with equal column 4 values.
How can this be done?
Thanks,
-Dale-
RE: Sorting a matrix? - DrD - 06-18-2015 03:26 PM
This is bulky, but seems to work (better ideas?):
Code:
EXPORT sm(N)
BEGIN
M1:=CAS("randMat(N,3,ip(1..10))"); // Generate random M1(N,3) cut list: M1[#pieces,length,width] of N patterns
for I from 1 to length(M1) do
M1(I,4):=M1(I,2)*M1(I,3); // Create column 4, M1[#pieces,length,width,area]
end;
for I from 1 to length(M1) do
for J from I+1 to length(M1) do
IF M1(I,4)<M1(J,4) then SWAPROW(M1,J,I); end; // Sort column 4 in decreasing order
end; // J
end; // I
for I from 1 to length(M1)-1 do
for J from I+1 to length(M1) do
IF (M1(I,4)==M1(J,4)) AND (M1(I,2)<M1(J,2)) then SWAPROW(M1,I,J); end; // Then sort column 2 decreasing, if equal col 4 values
end; // j
end; // I
END;tnx,
-Dale-
RE: Sorting a matrix? - parisse - 06-19-2015 04:54 AM
Create a sort function, something like
f:=(x,y)->if y[4]!=x[4] then return x[4]>y[4] else return x[2]>y[2] end;
then sort(m,f) will sort a matrix m using f as a sort function.
RE: Sorting a matrix? - DrD - 06-19-2015 10:28 AM
Thank you for your very helpful suggestion! I like compact solutions like this, and I'll add it to my "how to" list for future reference.
-Dale-