calling array entry based on variable
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I have an array A and I want to call one of its entries. I want to predefine which entry by saying E='1,2' for example, and calling A(E). Is this possible?
EDIT:
I want to call A(1,2) but I want (1,2) to be defined before I call A(1,2)
So something like:
A=[1 2 3;4 5 6;7 8 9];
E='1,2';
A(E)
>>ans=2
回答（1 个）
Image Analyst
2015-4-7
What does E mean? And what are its dimensions? If it's a 1x2 array that means a row and column, then you'd have to do A(E(1), E(2)).
If you simply did A(E) it would take that to mean you want two elements, A(E(1)) and A(E(2)), using E as linear indexes , not rows and columns. Since linear indexes go down the first column, then down the second column, etc. across all the columns, then A(E) would get A(1,1) and A(2,1). Just try it and see:
A=magic(4)
E = [1,2]
A(E)
6 个评论
Image Analyst
2015-4-8
Josh's comment moved here:
I want to call A(1,2) but I want (1,2) to be defined before I call A(1,2)
So something like:
A=[1 2 3;4 5 6;7 8 9];
E='1,2';
A(E)
>>ans=2
James Tursa
2015-4-8
编辑：James Tursa
2015-4-8
Josh: Assuming E is really a string, use IA's method but turn your string into indexes first. E.g.,
>> A=[1 2 3;4 5 6;7 8 9];
>> E = '1,2';
>> X = str2num(E)
X =
1 2
>> A(X(1),X(2))
ans =
2
Image Analyst
2015-4-8
Josh, that is even worse . Now you have E as a string instead of a numerical array. Why? Isn't "E" a variable that you create in your program? Why make it hard on yourself? Why make it an N by 2 array, or even worse, a string? Why not just keep track of the rows in a rows array and the columns in a columns array, then just do A(rows, columns) to get all of them, or A(rows(k), columns(k)) to extract out just the k'th row and column?
Josh
2015-4-8
James Tursa
2015-4-8
Josh: Is E a string or isn't it? If it is a string, then does it have to be a string or can you make it simpler on yourself as IA suggests?
Image Analyst
2015-4-8
Oh great - now they're cells? Or cell arrays? It's getting even worse. Plus you have several of these cell arrays, not just one, with possibly with different variable names (other than the badly-named "E"). What is the size of the cell arrays, and inside each cell, is there a numerical array, and what is the size of that array? I really urge you to simplify your programming life.
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2015-4-8
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