how to efficiently encode two values as a unique entitiy

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balandong
balandong 2018-11-23
编辑： Jan 2018-11-26
Dear all,
With respect to the above subject, I wonder if we can make the following code more efficient and compact (reduce the ifelse)..
A=3;
B=3;
C=[];
if A==1 && B==1
C=1;
elseif A==1 && B==2
C=2;
elseif A==1 && B==3
C=3;
elseif A==2 && B==2
C=4;
elseif A==2 && B==3
C=5;
elseif A==3 && B==1
C=6;
elseif A==3 && B==2
C=7;
elseif A==3 && B==3
C=8;
end
In addition, I also wonder if we can scale it up for A=[2;2;3;1] and B= [1;1;3;1]
Thanks in advance

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采纳的回答

Jan
Jan 2018-11-23
编辑：Jan 2018-11-26
A = 3;
B = 3;
Q = [1, 1, 1, 2, 2, 3, 3, 3; ... % A
1, 2, 3, 2, 3, 1, 2, 3; ... % B
1, 2, 3, 4, 5, 6, 7, 8].'; % C
idx = ismember(Q(:, 1:2), [A, B], 'rows');
C = Q(idx, 3);
I do not know what " scale it up for A=[2;2;3;1] and B= [1;1;3;1]" means.

更多回答（1 个）

Jan
Jan 2018-11-23
编辑：Jan 2018-11-23
Start with a simplification by omitting repeated comparisons:
A = 3;
B = 3;
C = [];
if A == 1
if B == 1
C = 1;
elseif B == 2
C = 2;
elseif B == 3
C = 3;
end
elseif A == 2
if B == 2
C = 4;
elseif B == 3
C = 5;
end
elseif A == 3
if B == 1
C = 6;
elseif B == 2
C = 7;
elseif B == 3
C = 8;
end
end
This should run faster, but is not much nicer. What about switch ?
A = 3;
B = 3;
C = [];
switch A
case 1
switch B
case 1
C = 1;
case 2
C = 2;
case 3
C = 3;
end
case 2
switch B
case 2
C = 4;
case 3
C = 5;
end
case 3
switch B
case 1
C = 6;
case 2
C = 7;
case 3
C = 8;
end
end
end
Nope, not nicer also.

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