how to change variable name for iteration of vector computation?

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maryam 2014-10-20

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评论： Star Strider 2014-10-20

I am trying to create a loop that changes the variable name in each iteration, basically instead of coding " sec1_mean = mean(vel_sec1); sec2_mean = mean(vel_sec2); sec3_mean = mean(vel_sec3); sec4_mean = mean(vel_sec4); sec5_mean = mean(vel_sec5); sec6_mean = mean(vel_sec6); sec7_mean = mean(vel_sec7); " have a loop like

 for i = 1:7
    m_name2 = ['vel_sec' num2str(i)]
    ['sec' num2str(i) '_mean']= mean(m_name2)
 end

but I have got error with this loop and the problem is that m_name2's class is char whereas we need it as double so that we can get the mean of say vel_sec1. I would appreciate any help on how I can solve this error.

Thanks

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Answer 1

Matt J 2014-10-20

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编辑：Matt J 2014-10-20

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You should be holding your vel_sec data as cell array elements vel_sec{i} and do

for i=1:7
    sec_mean(i)=vel_sec{i};
end

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maryam 2014-10-20

Thanks Matt but I think what this do is a little bit different with what I have in mind. here, you are dealing with sec_mean as 1 matrix. I would like to make 7 matrices with the name changing at each loop(eg. sec1_mean, sec2_mean, etc) and the value that is in each matrix is the mean of 7 different matrices that are vel_sec1, vel_sec2, etc...)

Matt J 2014-10-20

编辑：Matt J 2014-10-20

Yes, I'm advising you not to do that and so is Star Strider. See also

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

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Answer 2

Star Strider 2014-10-20

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编辑：Star Strider 2014-10-20

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I suggest you create it as an array instead. It will be much easier to work with later:

for k1 = 1:7
    sec_mean(k1) = mean(eval(sprintf('vel_sec%d',k1)));
end

The mean of all seven matrices is then: mean(sec_mean).

It would be best also to convert the ‘vel_sec#’ vectors to arrays as well, and delete the separate variables. You could use a numeric or cell array for those.

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maryam 2014-10-20

编辑：maryam 2014-10-20

Thanks Star Strider.. So now I am converting them to arrays, but there is still an error as vel_sec1,... matrices have many rows and 4 columns, and I get this error for eval: eval(sprintf('vel_sec%d',k1)) Index exceeds matrix dimensions. Do you have any idea how I solve this error?

for k1 = 1:7 sec_mean(k1,1:4) = mean(eval(sprintf('vel_sec%d',k1))); end eval(sprintf('vel_sec%d',k1)) Index exceeds matrix dimensions.

Star Strider 2014-10-20

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The mean function defaults to taking the means of the columns. If you want to take the means of all the elements of each of the different matrices, this works:

% CREATE DATA
[vel_sec1, vel_sec2, vel_sec3, vel_sec4, vel_sec5, vel_sec6, vel_sec7] = deal(rand(3,4), rand(5,4), rand(7,4), rand(6,4), rand(3,4), rand(5,4),rand(4,4));
for k1 = 1:7
    sec_mean(k1) = mean(eval(sprintf('vel_sec%d(:)',k1)));
end
grand_mean = mean(sec_mean);