Vector Error

Question

Steve 2012-1-25

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/27102-vector-error

I am trying to read data from a serial port and store the values in a vector to eventually plot.

I keep getting the following error:

"In an assignment A(I) = B, the number of elements in B and I must be the same."

I understand that the data from the serial port may not be the same size, but I cannot figure out how to remedy this problem. Here is the basic program that I am testing with:

for i = 1 : 10

    y(i) = fread(s) 
end

I am also just using Hyperterminal to test.

Any help is much appreciated!

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Answer 1

David Young 2012-1-25

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https://ww2.mathworks.cn/matlabcentral/answers/27102-vector-error#answer_35269

在 MATLAB Online 中打开

A call to fread returns a vector, but you can only store a single number in y(i) if i is a scalar (which it is in your code - i is one of the numbers from 1 to 10).

The solution really depends on what you want to do with the data afterwards, but one possibility is to store each vector in one element of a cell array. To do this, you'd replace the second line of your code with

y{i} = fread(s);

(You could also preallocate y before the loop, using

y = cell(1, 10);

)

This keeps the data from each call to fread separate.

If you want to combine the vectors into one big vector, you can do

y = [];
for i = 1:10
  y = [y; fread(s)];
end

You may well need to make your code more complex in order to read successfully from the serial port - for example, you may need to test BytesAvailable(s) to see whether to continue the loop or pause.