Error with the division

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Pul
Pul 2021-11-25
评论： Star Strider 2021-11-30
Hello everyone,
load('DATI_MAR_ANNUALI');
load('DATA_ECM');
a=DATIMARannuali;
b=DATIECMWFannuali;
c=(a-b)./a
d=c*100
this is my code, but I get an error trying to do the division; how can I solve it?
Thank you!
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Mathieu NOE
Mathieu NOE 2021-11-26
hello @Pul
can you explain what is the intention ? the tables contain multiple columns so the math you want to do is for which ones ?
Pul
Pul 2021-11-30
Exactly, but I solved the problem. Thank you!

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Star Strider
Star Strider 2021-11-26
Use the table2array function to convert the contents of the table to an array. Assign the arrays to new variables rather than over-writing the tables, since the references in the tables may be useful later in the code.
However the first column of the (40x13) table ‘DATIMARannuali’ is a year value (not a datetime array) with the variable name 'Year' so including that in the calculation may not be appropriate. While I did not download and open ‘DATA_ECM.mat’ the sizes of the two tables must match for tthe element-wise calculations to succeed, and the variables must be the same (or have similar contexts) for the calculation to make any sense.
.
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Pul
Pul 2021-11-30
Okay, got it. I solved it.
Thank you!
Star Strider
Star Strider 2021-11-30
As always, my pleasure!
.

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Peter Perkins
Peter Perkins 2021-11-26
As StarStride hints, these tables are not even the same size, in either dimension:
>> DATIECMWFannuali
DATIECMWFannuali =
24×17 table
[snip]
>> DATIMARannuali
DATIMARannuali =
40×13 table
[snip]
If they were, there are a few ways to do this, all more or less syntactic variations on the same thing: a table is a container, and you need to do the math on the contents, not the container. As SS points out, one of the variables in these tables is a year number, and surely you dont want to include that in the calculation. So first, probably, convert to timetables.
Given that, the simplest thing would be something like
c = (DATIECMWFannuali.Variables-DATIMARannuali.Variables)./DATIECMWFannuali.Variables;
d = array2table(c*100,'VariableNames',DATIECMWFannuali.Properties.VariableNames);
or perhaps
a = DATIECMWFannuali.Variables; % or DATIECMWFannuali{:,:}, or table2array(DATIECMWFannuali)
b = DATIMARannuali.Variables; % or ...
c = (b-a)./a;
d = array2table(c*100,'VariableNames',DATIECMWFannuali.Properties.VariableNames);
If you leave them as tables, then probably the ...{:,:} syntax is easiest, because you can use ...{:,2:end}.
The whole topic of "doing math on data in tables" is explored here: "This example ... shows how to perform calculations by using the numeric and categorical data that the table contains." You might find that helpful.

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