Plot data in loop with num2str

Question

yoni verhaegen 2018-7-23

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评论： Stephen23 2018-7-24

Hi all,

I want to plot a dynamic figure by plotting the sixth column of the datasets Meteo1752 to Meteo1966:

balyr=1752;
endyr=1966;
for k = balyr:endyr
  balanceyear(k-balyr+1,:)=k;
  plot(['Meteo' num2str(k) '(:,6)']);
end

However, the error says

Error using plot
Invalid first data argument.

What am I doing wrong?

Thanks

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Adam 2018-7-23

编辑：Adam 2018-7-23

在 MATLAB Online 中打开

doc plot

tells you what the valid data types are for the inputs. plot expects numeric data arguments (or an axes handle as first argument). You are giving it a string.

You'll have to give your actual data to the plot instruction, and probably you will need to use

doc hold

too.

Stephen23 2018-7-24

@yoni verhaegen: what you are trying to do is not recommended. Read this to know why:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

It is easy to avoid this situation: usually some indexing is the key.

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Answer 1

Dimitris Kalogiros 2018-7-23

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在 MATLAB Online 中打开

If you want to display something on your workspace, use disp() instead of plot()

balyr=1752;
endyr=1966;
for k = balyr:endyr
  balanceyear(k-balyr+1,:)=k;
  %plot(['Meteo' num2str(k) '(:,6)']);
  disp(['Meteo' num2str(k) '(:,6)']);
end

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Answer 2

dpb 2018-7-23

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编辑：dpb 2018-7-23

Several things...the specific error is trying to plot() a string; ML will not do character substitution like that.

The more fundamental issue is in having created the multiple variables with sequential names; as you've just discovered, now you have a problem in addressing them.

See the FAQ that talks about how to avoid the problem; we don't know how these were created so the best way to choose isn't clear.