Error in for and if cycles for average

Question

Stefano Alberti 2016-5-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/282291-error-in-for-and-if-cycles-for-average

评论： Stephen23 2016-5-3

Hi to all, I have some problems with this code. There is a error on 18th line (if m_misure(j,1)=data_corr) --> 'The expression to the left of the equals sign is not a valid target for an assignment.' Why ? I don't understand. I need a code to read a values series with dates and an average of these for each days (number of values for day is variable).

Thanks,

Stefano

%vettore colonna con data (solo giorno) - importazione
c_giorni=csvread(...)
%vettore colonna con valori - importazione
c_misurazioni=csvread(...)
%definiamo matrice formata dai due valori
m_misure=[c_giorni c_misurazioni];
%definiamo matrice in cui metteremo data e media
m_medie=[];
%definiamo ciclo for
for i=1:length(c_giorni)
if i>1 & m_misure(i,1) ~= m_misure(i-1,1)
somma_valori=0; 
numero_valori=0; 
data_corr=m_misure(i,1);
for j=1:length(c_giorni)
if m_misure(j,1)=data_corr
somma_valori=somma_valori+m_misure(j, 2);
numero_valori=numero_valori+1;
end
end
m_medie(i,1)=data_corr;
m_medie(i,2)=somma_valori/numero_valori;
end
end

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Answer 1

Stephen23 2016-5-3

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/282291-error-in-for-and-if-cycles-for-average#answer_220544

编辑：Stephen23 2016-5-3

在 MATLAB Online 中打开

Because you are using the wrong 'equals':

= is used for assignment of values to a variable.
== is used to test for logical equivalence.

This is why you should learn to read the documentation: it tells us how to use MATLAB. For whatever reason, beginners often seem to be allergic to reading the help, but it is really very easy to read!

In any case, you need to change that line to this:

if m_misure(j,1) == data_corr
                  ^

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Stefano Alberti 2016-5-3

编辑：Stefano Alberti 2016-5-3

For real my big problem is the code, its functionality not the error that i found alone....

Stephen23 2016-5-3

Rather than using loops, a much simpler solution for your task is to use accumarray. Have a look at this similar question:

http://www.mathworks.com/matlabcentral/answers/282063-average-all-variable-in-the-same-longitude-and-latitude-for-excel

Basically you need to do two steps:

use the third output of unique to get a set of indices
use these in indices in accumarray to collect the data into groups and apply your chosen function.

That's all. Use the internet to find examples.

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