Vector and matrix index operations

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Ionut Anghel
Ionut Anghel 2015-7-6
编辑： Stephen23 2019-6-25
Hi, My question is about vectors and matrix: Assuming I have vector (array) of strings: myvect={'101AA21' '101AA22' '101AA23' '102AA21' '102AA22'}; I have a matrix mymatrix=magic(5); I want to define a variable from myvect for each column of mymatrix such the results should be: 101AA21=mymatrix(:,1); 101AA22=mymatrix(:,2), etc
in order to do this:
myvect={'101AA21' '101AA22' '101AA23' '102AA21' '102AA22'}; mymatrix=magic(5); mynew_vect=char(myvect);
for i=1:length(mynew_vect) mynew_vect(i)== mymatrix(:,i); end
plot(101AA21, 102AA22, '-r');
Statment mynew_vect(i)== mymatrix(:,i); it is wrong but how can be defined . The real vector is 300, matrix is 70000X300
Thank you

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Keith Hooks
Keith Hooks 2015-7-6
You won't be able to vectors/matrices long with a variable name. I suggest using a table or structure for mynew_vect instead. However, the variable names you have are invalid for a structure element. They need to start with a character.
A table might have performance advantages over a structure that large. I couldn't say either way.
Using a structure:
names={'D101AA21' 'D101AA22' 'D101AA23' 'D102AA21' 'D102AA22'};
mymatrix=magic(5);
for i=1:length(names)
mynew_vect.(names{i})= mymatrix(:,i);
end
And with a table:
names={'101AA21' '101AA22' '101AA23' '102AA21' '102AA22'};
mymatrix=magic(5);
for i=1:length(names)
mynew_table.names{i}= mymatrix(:,i);
end
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John D'Errico
John D'Errico 2015-7-6
That the customers want an illegal variable name is not relevant. They cannot have it. Variables cannot have names that start with a number.
And even if they decide to choose better names, I would STRONGLY suggest following Stephen's excellent recommendations here. It is just a bad idea to do what you wish to do.
Ionut Anghel
Ionut Anghel 2015-7-7
Hi, Those variables are signals in a power plant defined in the early 1978. In order to get their licence some calculations are with specials codes. So, I cannot change the name of the variables. I write this part of the program to compare experimental data with their system code calculations. So, after 37 years of using those names for their parameters/variables they are very reluctant to any changes. Any way, thank you all. I proved all your solutions.

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更多回答（2 个）

Thorsten
Thorsten 2015-7-6
编辑：Thorsten 2015-7-6
Use eval:
myvect={'101AA21' '101AA22' '101AA23' '102AA21' '102AA22'};
mymatrix=magic(5);
for i = 1:numel(myvect)
eval(['var_' myvect{i} '= mymatrix(i,:);']);
end
plot(var_101AA21, var_101AA22)
And yes, I agree that this is awful code, but the closed to be able to write something as simple as (which seems to be what wanted here, for whatever reasons):
plot(101AA21, 101AA22)
  1 个评论
Steven Lord
Steven Lord 2015-7-6
DON'T use EVAL. Here's a slight modification of your code that avoids the EVAL while still getting close to the desired (illegal) code.
myvect={'101AA21' '101AA22' '101AA23' '102AA21' '102AA22'};
mymatrix = magic(5);
V = struct;
for k = 1:numel(myvect)
N = ['x' myvect{k}];
V.(N) = mymatrix(k, :);
end
plot(V.x101AA21, V.x101AA22)
Some prefix on the field name is necessary because MATLAB identifiers must start with a letter; I chose x.

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F.
F. 2015-7-8
What do you think about something like this :
myvect={'101AA21' '101AA22' '101AA23' '102AA21' '102AA22'};
mymatrix = magic(5);
Tmp1 = find( strcmp( myvect, '101AA21' ) );
Tmp2 = find( strcmp( myvect, '102AA21' ) );
plot( mymatrix(:,Tmp1), mymatrix(:,Tmp2) );
But perhaps, I didn't well understand what would you want to do with this variables...

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